1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
2304
2305
2306
2307
2308
2309
2310
2311
2312
2313
2314
2315
2316
2317
2318
2319
2320
2321
2322
2323
2324
2325
2326
2327
2328
2329
2330
2331
2332
2333
2334
2335
2336
2337
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
2362
2363
2364
2365
2366
2367
2368
2369
2370
2371
2372
2373
2374
2375
2376
2377
2378
2379
2380
2381
2382
2383
2384
2385
2386
2387
2388
2389
2390
2391
2392
2393
2394
2395
2396
2397
2398
2399
2400
2401
2402
2403
2404
2405
2406
2407
2408
2409
2410
2411
2412
2413
2414
2415
2416
2417
2418
2419
2420
2421
2422
2423
2424
2425
2426
2427
2428
2429
2430
2431
2432
2433
2434
2435
2436
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
2448
2449
2450
2451
2452
2453
2454
2455
2456
2457
2458
2459
2460
2461
2462
2463
2464
2465
2466
2467
2468
2469
2470
2471
2472
2473
2474
2475
2476
2477
2478
2479
2480
2481
2482
2483
2484
2485
2486
2487
2488
2489
2490
2491
2492
2493
2494
2495
2496
2497
2498
2499
2500
2501
2502
2503
2504
2505
2506
2507
2508
2509
2510
2511
2512
2513
2514
2515
2516
2517
2518
2519
2520
2521
2522
2523
2524
2525
2526
2527
2528
2529
2530
2531
2532
2533
2534
2535
2536
2537
2538
2539
2540
2541
2542
2543
2544
2545
2546
2547
2548
2549
2550
2551
2552
2553
2554
2555
2556
2557
2558
2559
2560
2561
2562
2563
2564
2565
2566
2567
2568
2569
2570
2571
2572
2573
2574
2575
2576
2577
2578
2579
2580
2581
2582
2583
2584
2585
2586
2587
2588
2589
2590
2591
2592
2593
2594
2595
2596
2597
2598
2599
2600
2601
2602
2603
2604
2605
2606
2607
2608
2609
2610
2611
2612
2613
2614
2615
2616
2617
2618
2619
2620
2621
2622
2623
2624
2625
2626
2627
2628
2629
2630
2631
2632
2633
2634
2635
2636
2637
2638
2639
2640
2641
2642
2643
2644
2645
2646
2647
2648
2649
2650
2651
2652
2653
2654
2655
2656
2657
2658
2659
2660
2661
2662
2663
2664
2665
2666
2667
2668
2669
2670
2671
2672
2673
2674
2675
2676
2677
2678
2679
2680
2681
2682
2683
2684
2685
2686
2687
2688
2689
2690
2691
2692
2693
2694
2695
2696
2697
2698
2699
2700
2701
2702
2703
2704
2705
2706
2707
2708
2709
2710
2711
2712
2713
2714
2715
2716
2717
2718
2719
2720
2721
2722
2723
2724
2725
2726
2727
2728
2729
2730
2731
2732
2733
2734
2735
2736
2737
2738
2739
2740
2741
2742
2743
2744
2745
2746
2747
2748
2749
2750
2751
2752
2753
2754
2755
2756
2757
2758
2759
2760
2761
2762
2763
2764
2765
2766
2767
2768
2769
2770
2771
2772
2773
2774
2775
2776
2777
2778
2779
2780
2781
2782
2783
2784
2785
2786
2787
2788
2789
2790
2791
2792
2793
2794
2795
2796
2797
2798
2799
2800
2801
2802
2803
2804
2805
2806
2807
2808
2809
2810
2811
2812
2813
2814
2815
2816
2817
2818
2819
2820
2821
2822
2823
2824
2825
2826
2827
2828
2829
2830
2831
2832
2833
2834
2835
2836
2837
2838
2839
2840
2841
2842
2843
2844
2845
2846
2847
2848
2849
2850
2851
2852
2853
2854
2855
2856
2857
2858
2859
2860
2861
2862
2863
2864
2865
2866
2867
2868
2869
2870
2871
2872
2873
2874
2875
2876
2877
2878
2879
2880
2881
2882
2883
2884
2885
2886
2887
2888
2889
2890
2891
2892
2893
2894
2895
2896
2897
2898
2899
2900
2901
2902
2903
2904
2905
2906
2907
2908
2909
2910
2911
2912
2913
2914
2915
2916
2917
2918
2919
2920
2921
2922
2923
2924
2925
2926
2927
2928
2929
2930
2931
2932
2933
2934
2935
2936
2937
2938
2939
2940
2941
2942
2943
2944
2945
2946
2947
2948
2949
2950
2951
2952
2953
2954
2955
2956
2957
2958
2959
2960
2961
2962
2963
2964
2965
2966
2967
2968
2969
2970
2971
2972
2973
2974
2975
2976
2977
2978
2979
2980
2981
2982
2983
2984
2985
2986
2987
2988
2989
2990
2991
2992
2993
2994
2995
2996
2997
2998
2999
3000
3001
3002
3003
3004
3005
3006
3007
3008
3009
3010
3011
3012
3013
3014
3015
3016
3017
3018
3019
3020
3021
3022
3023
3024
3025
3026
3027
3028
3029
3030
3031
3032
3033
3034
3035
3036
3037
3038
3039
3040
3041
3042
3043
3044
3045
3046
3047
3048
3049
3050
3051
3052
3053
3054
3055
3056
3057
3058
3059
3060
3061
3062
3063
3064
3065
3066
3067
3068
3069
3070
3071
3072
3073
3074
3075
3076
3077
3078
3079
3080
3081
3082
3083
3084
3085
3086
3087
3088
3089
3090
3091
3092
3093
3094
3095
3096
3097
3098
3099
3100
3101
3102
3103
3104
3105
3106
3107
3108
3109
3110
3111
3112
3113
3114
3115
3116
3117
3118
3119
3120
3121
3122
3123
3124
3125
3126
3127
3128
3129
3130
3131
3132
3133
3134
3135
3136
3137
3138
3139
3140
3141
3142
3143
3144
3145
3146
3147
3148
3149
3150
3151
3152
3153
3154
3155
3156
3157
3158
3159
3160
3161
3162
3163
3164
3165
3166
3167
3168
3169
3170
3171
3172
3173
3174
3175
3176
3177
3178
3179
3180
3181
3182
3183
3184
3185
3186
3187
3188
3189
3190
3191
3192
3193
3194
3195
3196
3197
3198
3199
3200
3201
3202
3203
3204
3205
3206
3207
3208
3209
3210
3211
3212
3213
3214
3215
3216
3217
3218
3219
3220
3221
3222
3223
3224
3225
3226
3227
3228
3229
3230
3231
3232
3233
3234
3235
3236
3237
3238
3239
3240
3241
3242
3243
3244
3245
3246
3247
3248
3249
3250
3251
3252
3253
3254
3255
3256
3257
3258
3259
3260
3261
3262
3263
3264
3265
3266
3267
3268
3269
3270
3271
3272
3273
3274
3275
3276
3277
3278
3279
3280
3281
3282
3283
3284
3285
3286
3287
3288
3289
3290
3291
3292
3293
3294
3295
3296
3297
3298
3299
3300
3301
3302
3303
3304
3305
3306
3307
3308
3309
3310
3311
3312
3313
3314
3315
3316
3317
3318
3319
3320
3321
3322
3323
3324
3325
3326
3327
3328
3329
3330
3331
3332
3333
3334
3335
3336
3337
3338
3339
3340
3341
3342
3343
3344
3345
3346
3347
3348
3349
3350
3351
3352
3353
3354
3355
3356
3357
3358
3359
3360
3361
3362
3363
3364
3365
3366
3367
3368
3369
3370
3371
3372
3373
3374
3375
3376
3377
3378
3379
3380
3381
3382
3383
3384
3385
3386
3387
3388
3389
3390
3391
3392
3393
3394
3395
3396
3397
3398
3399
3400
3401
3402
3403
3404
3405
3406
3407
3408
3409
3410
3411
3412
// ignore-tidy-filelength

use crate::diagnostics::{ImportSuggestion, LabelSuggestion, TypoSuggestion};
use crate::late::{AliasPossibility, LateResolutionVisitor, RibKind};
use crate::late::{LifetimeBinderKind, LifetimeRes, LifetimeRibKind, LifetimeUseSet};
use crate::ty::fast_reject::SimplifiedType;
use crate::{errors, path_names_to_string};
use crate::{Module, ModuleKind, ModuleOrUniformRoot};
use crate::{PathResult, PathSource, Segment};
use rustc_hir::def::Namespace::{self, *};

use rustc_ast::ptr::P;
use rustc_ast::visit::{walk_ty, FnCtxt, FnKind, LifetimeCtxt, Visitor};
use rustc_ast::{
    self as ast, AssocItemKind, Expr, ExprKind, GenericParam, GenericParamKind, Item, ItemKind,
    MethodCall, NodeId, Path, Ty, TyKind, DUMMY_NODE_ID,
};
use rustc_ast_pretty::pprust::where_bound_predicate_to_string;
use rustc_data_structures::fx::FxHashSet;
use rustc_errors::{
    codes::*, pluralize, struct_span_code_err, Applicability, Diag, ErrorGuaranteed, MultiSpan,
    SuggestionStyle,
};
use rustc_hir as hir;
use rustc_hir::def::{self, CtorKind, CtorOf, DefKind};
use rustc_hir::def_id::{DefId, CRATE_DEF_ID};
use rustc_hir::{MissingLifetimeKind, PrimTy};
use rustc_session::lint;
use rustc_session::Session;
use rustc_span::edit_distance::find_best_match_for_name;
use rustc_span::edition::Edition;
use rustc_span::hygiene::MacroKind;
use rustc_span::symbol::{kw, sym, Ident, Symbol};
use rustc_span::Span;

use rustc_middle::ty;

use std::borrow::Cow;
use std::iter;
use std::ops::Deref;

use thin_vec::ThinVec;

use super::NoConstantGenericsReason;

type Res = def::Res<ast::NodeId>;

/// A field or associated item from self type suggested in case of resolution failure.
enum AssocSuggestion {
    Field(Span),
    MethodWithSelf { called: bool },
    AssocFn { called: bool },
    AssocType,
    AssocConst,
}

impl AssocSuggestion {
    fn action(&self) -> &'static str {
        match self {
            AssocSuggestion::Field(_) => "use the available field",
            AssocSuggestion::MethodWithSelf { called: true } => {
                "call the method with the fully-qualified path"
            }
            AssocSuggestion::MethodWithSelf { called: false } => {
                "refer to the method with the fully-qualified path"
            }
            AssocSuggestion::AssocFn { called: true } => "call the associated function",
            AssocSuggestion::AssocFn { called: false } => "refer to the associated function",
            AssocSuggestion::AssocConst => "use the associated `const`",
            AssocSuggestion::AssocType => "use the associated type",
        }
    }
}

fn is_self_type(path: &[Segment], namespace: Namespace) -> bool {
    namespace == TypeNS && path.len() == 1 && path[0].ident.name == kw::SelfUpper
}

fn is_self_value(path: &[Segment], namespace: Namespace) -> bool {
    namespace == ValueNS && path.len() == 1 && path[0].ident.name == kw::SelfLower
}

/// Gets the stringified path for an enum from an `ImportSuggestion` for an enum variant.
fn import_candidate_to_enum_paths(suggestion: &ImportSuggestion) -> (String, String) {
    let variant_path = &suggestion.path;
    let variant_path_string = path_names_to_string(variant_path);

    let path_len = suggestion.path.segments.len();
    let enum_path = ast::Path {
        span: suggestion.path.span,
        segments: suggestion.path.segments[0..path_len - 1].iter().cloned().collect(),
        tokens: None,
    };
    let enum_path_string = path_names_to_string(&enum_path);

    (variant_path_string, enum_path_string)
}

/// Description of an elided lifetime.
#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Debug)]
pub(super) struct MissingLifetime {
    /// Used to overwrite the resolution with the suggestion, to avoid cascading errors.
    pub id: NodeId,
    /// Where to suggest adding the lifetime.
    pub span: Span,
    /// How the lifetime was introduced, to have the correct space and comma.
    pub kind: MissingLifetimeKind,
    /// Number of elided lifetimes, used for elision in path.
    pub count: usize,
}

/// Description of the lifetimes appearing in a function parameter.
/// This is used to provide a literal explanation to the elision failure.
#[derive(Clone, Debug)]
pub(super) struct ElisionFnParameter {
    /// The index of the argument in the original definition.
    pub index: usize,
    /// The name of the argument if it's a simple ident.
    pub ident: Option<Ident>,
    /// The number of lifetimes in the parameter.
    pub lifetime_count: usize,
    /// The span of the parameter.
    pub span: Span,
}

/// Description of lifetimes that appear as candidates for elision.
/// This is used to suggest introducing an explicit lifetime.
#[derive(Debug)]
pub(super) enum LifetimeElisionCandidate {
    /// This is not a real lifetime.
    Ignore,
    /// There is a named lifetime, we won't suggest anything.
    Named,
    Missing(MissingLifetime),
}

/// Only used for diagnostics.
#[derive(Debug)]
struct BaseError {
    msg: String,
    fallback_label: String,
    span: Span,
    span_label: Option<(Span, &'static str)>,
    could_be_expr: bool,
    suggestion: Option<(Span, &'static str, String)>,
    module: Option<DefId>,
}

#[derive(Debug)]
enum TypoCandidate {
    Typo(TypoSuggestion),
    Shadowed(Res, Option<Span>),
    None,
}

impl TypoCandidate {
    fn to_opt_suggestion(self) -> Option<TypoSuggestion> {
        match self {
            TypoCandidate::Typo(sugg) => Some(sugg),
            TypoCandidate::Shadowed(_, _) | TypoCandidate::None => None,
        }
    }
}

impl<'a: 'ast, 'ast, 'tcx> LateResolutionVisitor<'a, '_, 'ast, 'tcx> {
    fn make_base_error(
        &mut self,
        path: &[Segment],
        span: Span,
        source: PathSource<'_>,
        res: Option<Res>,
    ) -> BaseError {
        // Make the base error.
        let mut expected = source.descr_expected();
        let path_str = Segment::names_to_string(path);
        let item_str = path.last().unwrap().ident;
        if let Some(res) = res {
            BaseError {
                msg: format!("expected {}, found {} `{}`", expected, res.descr(), path_str),
                fallback_label: format!("not a {expected}"),
                span,
                span_label: match res {
                    Res::Def(DefKind::TyParam, def_id) => {
                        Some((self.r.def_span(def_id), "found this type parameter"))
                    }
                    _ => None,
                },
                could_be_expr: match res {
                    Res::Def(DefKind::Fn, _) => {
                        // Verify whether this is a fn call or an Fn used as a type.
                        self.r
                            .tcx
                            .sess
                            .source_map()
                            .span_to_snippet(span)
                            .is_ok_and(|snippet| snippet.ends_with(')'))
                    }
                    Res::Def(
                        DefKind::Ctor(..) | DefKind::AssocFn | DefKind::Const | DefKind::AssocConst,
                        _,
                    )
                    | Res::SelfCtor(_)
                    | Res::PrimTy(_)
                    | Res::Local(_) => true,
                    _ => false,
                },
                suggestion: None,
                module: None,
            }
        } else {
            let mut span_label = None;
            let item_ident = path.last().unwrap().ident;
            let item_span = item_ident.span;
            let (mod_prefix, mod_str, module, suggestion) = if path.len() == 1 {
                debug!(?self.diag_metadata.current_impl_items);
                debug!(?self.diag_metadata.current_function);
                let suggestion = if self.current_trait_ref.is_none()
                    && let Some((fn_kind, _)) = self.diag_metadata.current_function
                    && let Some(FnCtxt::Assoc(_)) = fn_kind.ctxt()
                    && let FnKind::Fn(_, _, sig, ..) = fn_kind
                    && let Some(items) = self.diag_metadata.current_impl_items
                    && let Some(item) = items.iter().find(|i| {
                        i.ident.name == item_str.name
                            // Don't suggest if the item is in Fn signature arguments (#112590).
                            && !sig.span.contains(item_span)
                    }) {
                    let sp = item_span.shrink_to_lo();

                    // Account for `Foo { field }` when suggesting `self.field` so we result on
                    // `Foo { field: self.field }`.
                    let field = match source {
                        PathSource::Expr(Some(Expr { kind: ExprKind::Struct(expr), .. })) => {
                            expr.fields.iter().find(|f| f.ident == item_ident)
                        }
                        _ => None,
                    };
                    let pre = if let Some(field) = field
                        && field.is_shorthand
                    {
                        format!("{item_ident}: ")
                    } else {
                        String::new()
                    };
                    // Ensure we provide a structured suggestion for an assoc fn only for
                    // expressions that are actually a fn call.
                    let is_call = match field {
                        Some(ast::ExprField { expr, .. }) => {
                            matches!(expr.kind, ExprKind::Call(..))
                        }
                        _ => matches!(
                            source,
                            PathSource::Expr(Some(Expr { kind: ExprKind::Call(..), .. })),
                        ),
                    };

                    match &item.kind {
                        AssocItemKind::Fn(fn_)
                            if (!sig.decl.has_self() || !is_call) && fn_.sig.decl.has_self() =>
                        {
                            // Ensure that we only suggest `self.` if `self` is available,
                            // you can't call `fn foo(&self)` from `fn bar()` (#115992).
                            // We also want to mention that the method exists.
                            span_label = Some((
                                item.ident.span,
                                "a method by that name is available on `Self` here",
                            ));
                            None
                        }
                        AssocItemKind::Fn(fn_) if !fn_.sig.decl.has_self() && !is_call => {
                            span_label = Some((
                                item.ident.span,
                                "an associated function by that name is available on `Self` here",
                            ));
                            None
                        }
                        AssocItemKind::Fn(fn_) if fn_.sig.decl.has_self() => {
                            Some((sp, "consider using the method on `Self`", format!("{pre}self.")))
                        }
                        AssocItemKind::Fn(_) => Some((
                            sp,
                            "consider using the associated function on `Self`",
                            format!("{pre}Self::"),
                        )),
                        AssocItemKind::Const(..) => Some((
                            sp,
                            "consider using the associated constant on `Self`",
                            format!("{pre}Self::"),
                        )),
                        _ => None,
                    }
                } else {
                    None
                };
                (String::new(), "this scope".to_string(), None, suggestion)
            } else if path.len() == 2 && path[0].ident.name == kw::PathRoot {
                if self.r.tcx.sess.edition() > Edition::Edition2015 {
                    // In edition 2018 onwards, the `::foo` syntax may only pull from the extern prelude
                    // which overrides all other expectations of item type
                    expected = "crate";
                    (String::new(), "the list of imported crates".to_string(), None, None)
                } else {
                    (
                        String::new(),
                        "the crate root".to_string(),
                        Some(CRATE_DEF_ID.to_def_id()),
                        None,
                    )
                }
            } else if path.len() == 2 && path[0].ident.name == kw::Crate {
                (String::new(), "the crate root".to_string(), Some(CRATE_DEF_ID.to_def_id()), None)
            } else {
                let mod_path = &path[..path.len() - 1];
                let mod_res = self.resolve_path(mod_path, Some(TypeNS), None);
                let mod_prefix = match mod_res {
                    PathResult::Module(ModuleOrUniformRoot::Module(module)) => module.res(),
                    _ => None,
                };

                let module_did = mod_prefix.as_ref().and_then(Res::mod_def_id);

                let mod_prefix =
                    mod_prefix.map_or_else(String::new, |res| (format!("{} ", res.descr())));

                (mod_prefix, format!("`{}`", Segment::names_to_string(mod_path)), module_did, None)
            };

            let (fallback_label, suggestion) = if path_str == "async"
                && expected.starts_with("struct")
            {
                ("`async` blocks are only allowed in Rust 2018 or later".to_string(), suggestion)
            } else {
                // check if we are in situation of typo like `True` instead of `true`.
                let override_suggestion =
                    if ["true", "false"].contains(&item_str.to_string().to_lowercase().as_str()) {
                        let item_typo = item_str.to_string().to_lowercase();
                        Some((item_span, "you may want to use a bool value instead", item_typo))
                    // FIXME(vincenzopalazzo): make the check smarter,
                    // and maybe expand with levenshtein distance checks
                    } else if item_str.as_str() == "printf" {
                        Some((
                            item_span,
                            "you may have meant to use the `print` macro",
                            "print!".to_owned(),
                        ))
                    } else {
                        suggestion
                    };
                (format!("not found in {mod_str}"), override_suggestion)
            };

            BaseError {
                msg: format!("cannot find {expected} `{item_str}` in {mod_prefix}{mod_str}"),
                fallback_label,
                span: item_span,
                span_label,
                could_be_expr: false,
                suggestion,
                module,
            }
        }
    }

    /// Try to suggest for a module path that cannot be resolved.
    /// Such as `fmt::Debug` where `fmt` is not resolved without importing,
    /// here we search with `lookup_import_candidates` for a module named `fmt`
    /// with `TypeNS` as namespace.
    ///
    /// We need a separate function here because we won't suggest for a path with single segment
    /// and we won't change `SourcePath` api `is_expected` to match `Type` with `DefKind::Mod`
    pub(crate) fn smart_resolve_partial_mod_path_errors(
        &mut self,
        prefix_path: &[Segment],
        following_seg: Option<&Segment>,
    ) -> Vec<ImportSuggestion> {
        if let Some(segment) = prefix_path.last()
            && let Some(following_seg) = following_seg
        {
            let candidates = self.r.lookup_import_candidates(
                segment.ident,
                Namespace::TypeNS,
                &self.parent_scope,
                &|res: Res| matches!(res, Res::Def(DefKind::Mod, _)),
            );
            // double check next seg is valid
            candidates
                .into_iter()
                .filter(|candidate| {
                    if let Some(def_id) = candidate.did
                        && let Some(module) = self.r.get_module(def_id)
                    {
                        Some(def_id) != self.parent_scope.module.opt_def_id()
                            && self
                                .r
                                .resolutions(module)
                                .borrow()
                                .iter()
                                .any(|(key, _r)| key.ident.name == following_seg.ident.name)
                    } else {
                        false
                    }
                })
                .collect::<Vec<_>>()
        } else {
            Vec::new()
        }
    }

    /// Handles error reporting for `smart_resolve_path_fragment` function.
    /// Creates base error and amends it with one short label and possibly some longer helps/notes.
    pub(crate) fn smart_resolve_report_errors(
        &mut self,
        path: &[Segment],
        following_seg: Option<&Segment>,
        span: Span,
        source: PathSource<'_>,
        res: Option<Res>,
    ) -> (Diag<'tcx>, Vec<ImportSuggestion>) {
        debug!(?res, ?source);
        let base_error = self.make_base_error(path, span, source, res);

        let code = source.error_code(res.is_some());
        let mut err = self.r.dcx().struct_span_err(base_error.span, base_error.msg.clone());
        err.code(code);

        self.suggest_at_operator_in_slice_pat_with_range(&mut err, path);
        self.suggest_swapping_misplaced_self_ty_and_trait(&mut err, source, res, base_error.span);

        if let Some((span, label)) = base_error.span_label {
            err.span_label(span, label);
        }

        if let Some(ref sugg) = base_error.suggestion {
            err.span_suggestion_verbose(sugg.0, sugg.1, &sugg.2, Applicability::MaybeIncorrect);
        }

        self.suggest_bare_struct_literal(&mut err);
        self.suggest_changing_type_to_const_param(&mut err, res, source, span);

        if self.suggest_pattern_match_with_let(&mut err, source, span) {
            // Fallback label.
            err.span_label(base_error.span, base_error.fallback_label);
            return (err, Vec::new());
        }

        self.suggest_self_or_self_ref(&mut err, path, span);
        self.detect_assoc_type_constraint_meant_as_path(&mut err, &base_error);
        if self.suggest_self_ty(&mut err, source, path, span)
            || self.suggest_self_value(&mut err, source, path, span)
        {
            return (err, Vec::new());
        }

        let (found, mut candidates) = self.try_lookup_name_relaxed(
            &mut err,
            source,
            path,
            following_seg,
            span,
            res,
            &base_error,
        );
        if found {
            return (err, candidates);
        }

        if self.suggest_shadowed(&mut err, source, path, following_seg, span) {
            // if there is already a shadowed name, don'suggest candidates for importing
            candidates.clear();
        }

        let mut fallback = self.suggest_trait_and_bounds(&mut err, source, res, span, &base_error);
        fallback |= self.suggest_typo(&mut err, source, path, following_seg, span, &base_error);

        if fallback {
            // Fallback label.
            err.span_label(base_error.span, base_error.fallback_label);
        }
        self.err_code_special_cases(&mut err, source, path, span);

        if let Some(module) = base_error.module {
            self.r.find_cfg_stripped(&mut err, &path.last().unwrap().ident.name, module);
        }

        (err, candidates)
    }

    fn detect_assoc_type_constraint_meant_as_path(
        &self,
        err: &mut Diag<'_>,
        base_error: &BaseError,
    ) {
        let Some(ty) = self.diag_metadata.current_type_path else {
            return;
        };
        let TyKind::Path(_, path) = &ty.kind else {
            return;
        };
        for segment in &path.segments {
            let Some(params) = &segment.args else {
                continue;
            };
            let ast::GenericArgs::AngleBracketed(ref params) = params.deref() else {
                continue;
            };
            for param in &params.args {
                let ast::AngleBracketedArg::Constraint(constraint) = param else {
                    continue;
                };
                let ast::AssocConstraintKind::Bound { bounds } = &constraint.kind else {
                    continue;
                };
                for bound in bounds {
                    let ast::GenericBound::Trait(trait_ref, ast::TraitBoundModifiers::NONE) = bound
                    else {
                        continue;
                    };
                    if base_error.span == trait_ref.span {
                        err.span_suggestion_verbose(
                            constraint.ident.span.between(trait_ref.span),
                            "you might have meant to write a path instead of an associated type bound",
                            "::",
                            Applicability::MachineApplicable,
                        );
                    }
                }
            }
        }
    }

    fn suggest_self_or_self_ref(&mut self, err: &mut Diag<'_>, path: &[Segment], span: Span) {
        if !self.self_type_is_available() {
            return;
        }
        let Some(path_last_segment) = path.last() else { return };
        let item_str = path_last_segment.ident;
        // Emit help message for fake-self from other languages (e.g., `this` in JavaScript).
        if ["this", "my"].contains(&item_str.as_str()) {
            err.span_suggestion_short(
                span,
                "you might have meant to use `self` here instead",
                "self",
                Applicability::MaybeIncorrect,
            );
            if !self.self_value_is_available(path[0].ident.span) {
                if let Some((FnKind::Fn(_, _, sig, ..), fn_span)) =
                    &self.diag_metadata.current_function
                {
                    let (span, sugg) = if let Some(param) = sig.decl.inputs.get(0) {
                        (param.span.shrink_to_lo(), "&self, ")
                    } else {
                        (
                            self.r
                                .tcx
                                .sess
                                .source_map()
                                .span_through_char(*fn_span, '(')
                                .shrink_to_hi(),
                            "&self",
                        )
                    };
                    err.span_suggestion_verbose(
                        span,
                        "if you meant to use `self`, you are also missing a `self` receiver \
                         argument",
                        sugg,
                        Applicability::MaybeIncorrect,
                    );
                }
            }
        }
    }

    fn try_lookup_name_relaxed(
        &mut self,
        err: &mut Diag<'_>,
        source: PathSource<'_>,
        path: &[Segment],
        following_seg: Option<&Segment>,
        span: Span,
        res: Option<Res>,
        base_error: &BaseError,
    ) -> (bool, Vec<ImportSuggestion>) {
        // Try to lookup name in more relaxed fashion for better error reporting.
        let ident = path.last().unwrap().ident;
        let is_expected = &|res| source.is_expected(res);
        let ns = source.namespace();
        let is_enum_variant = &|res| matches!(res, Res::Def(DefKind::Variant, _));
        let path_str = Segment::names_to_string(path);
        let ident_span = path.last().map_or(span, |ident| ident.ident.span);
        let mut candidates = self
            .r
            .lookup_import_candidates(ident, ns, &self.parent_scope, is_expected)
            .into_iter()
            .filter(|ImportSuggestion { did, .. }| {
                match (did, res.and_then(|res| res.opt_def_id())) {
                    (Some(suggestion_did), Some(actual_did)) => *suggestion_did != actual_did,
                    _ => true,
                }
            })
            .collect::<Vec<_>>();
        // Try to filter out intrinsics candidates, as long as we have
        // some other candidates to suggest.
        let intrinsic_candidates: Vec<_> = candidates
            .extract_if(|sugg| {
                let path = path_names_to_string(&sugg.path);
                path.starts_with("core::intrinsics::") || path.starts_with("std::intrinsics::")
            })
            .collect();
        if candidates.is_empty() {
            // Put them back if we have no more candidates to suggest...
            candidates = intrinsic_candidates;
        }
        let crate_def_id = CRATE_DEF_ID.to_def_id();
        if candidates.is_empty() && is_expected(Res::Def(DefKind::Enum, crate_def_id)) {
            let mut enum_candidates: Vec<_> = self
                .r
                .lookup_import_candidates(ident, ns, &self.parent_scope, is_enum_variant)
                .into_iter()
                .map(|suggestion| import_candidate_to_enum_paths(&suggestion))
                .filter(|(_, enum_ty_path)| !enum_ty_path.starts_with("std::prelude::"))
                .collect();
            if !enum_candidates.is_empty() {
                enum_candidates.sort();

                // Contextualize for E0412 "cannot find type", but don't belabor the point
                // (that it's a variant) for E0573 "expected type, found variant".
                let preamble = if res.is_none() {
                    let others = match enum_candidates.len() {
                        1 => String::new(),
                        2 => " and 1 other".to_owned(),
                        n => format!(" and {n} others"),
                    };
                    format!("there is an enum variant `{}`{}; ", enum_candidates[0].0, others)
                } else {
                    String::new()
                };
                let msg = format!("{preamble}try using the variant's enum");

                err.span_suggestions(
                    span,
                    msg,
                    enum_candidates.into_iter().map(|(_variant_path, enum_ty_path)| enum_ty_path),
                    Applicability::MachineApplicable,
                );
            }
        }

        // Try finding a suitable replacement.
        let typo_sugg = self
            .lookup_typo_candidate(path, following_seg, source.namespace(), is_expected)
            .to_opt_suggestion();
        if path.len() == 1
            && !matches!(source, PathSource::Delegation)
            && self.self_type_is_available()
        {
            if let Some(candidate) =
                self.lookup_assoc_candidate(ident, ns, is_expected, source.is_call())
            {
                let self_is_available = self.self_value_is_available(path[0].ident.span);
                // Account for `Foo { field }` when suggesting `self.field` so we result on
                // `Foo { field: self.field }`.
                let pre = match source {
                    PathSource::Expr(Some(Expr { kind: ExprKind::Struct(expr), .. }))
                        if expr
                            .fields
                            .iter()
                            .any(|f| f.ident == path[0].ident && f.is_shorthand) =>
                    {
                        format!("{path_str}: ")
                    }
                    _ => String::new(),
                };
                match candidate {
                    AssocSuggestion::Field(field_span) => {
                        if self_is_available {
                            err.span_suggestion_verbose(
                                span.shrink_to_lo(),
                                "you might have meant to use the available field",
                                format!("{pre}self."),
                                Applicability::MachineApplicable,
                            );
                        } else {
                            err.span_label(field_span, "a field by that name exists in `Self`");
                        }
                    }
                    AssocSuggestion::MethodWithSelf { called } if self_is_available => {
                        let msg = if called {
                            "you might have meant to call the method"
                        } else {
                            "you might have meant to refer to the method"
                        };
                        err.span_suggestion_verbose(
                            span.shrink_to_lo(),
                            msg,
                            "self.",
                            Applicability::MachineApplicable,
                        );
                    }
                    AssocSuggestion::MethodWithSelf { .. }
                    | AssocSuggestion::AssocFn { .. }
                    | AssocSuggestion::AssocConst
                    | AssocSuggestion::AssocType => {
                        err.span_suggestion_verbose(
                            span.shrink_to_lo(),
                            format!("you might have meant to {}", candidate.action()),
                            "Self::",
                            Applicability::MachineApplicable,
                        );
                    }
                }
                self.r.add_typo_suggestion(err, typo_sugg, ident_span);
                return (true, candidates);
            }

            // If the first argument in call is `self` suggest calling a method.
            if let Some((call_span, args_span)) = self.call_has_self_arg(source) {
                let mut args_snippet = String::new();
                if let Some(args_span) = args_span {
                    if let Ok(snippet) = self.r.tcx.sess.source_map().span_to_snippet(args_span) {
                        args_snippet = snippet;
                    }
                }

                err.span_suggestion(
                    call_span,
                    format!("try calling `{ident}` as a method"),
                    format!("self.{path_str}({args_snippet})"),
                    Applicability::MachineApplicable,
                );
                return (true, candidates);
            }
        }

        // Try context-dependent help if relaxed lookup didn't work.
        if let Some(res) = res {
            if self.smart_resolve_context_dependent_help(
                err,
                span,
                source,
                path,
                res,
                &path_str,
                &base_error.fallback_label,
            ) {
                // We do this to avoid losing a secondary span when we override the main error span.
                self.r.add_typo_suggestion(err, typo_sugg, ident_span);
                return (true, candidates);
            }
        }

        // Try to find in last block rib
        if let Some(rib) = &self.last_block_rib
            && let RibKind::Normal = rib.kind
        {
            for (ident, &res) in &rib.bindings {
                if let Res::Local(_) = res
                    && path.len() == 1
                    && ident.span.eq_ctxt(path[0].ident.span)
                    && ident.name == path[0].ident.name
                {
                    err.span_help(
                        ident.span,
                        format!("the binding `{path_str}` is available in a different scope in the same function"),
                    );
                    return (true, candidates);
                }
            }
        }

        if candidates.is_empty() {
            candidates = self.smart_resolve_partial_mod_path_errors(path, following_seg);
        }

        return (false, candidates);
    }

    fn suggest_trait_and_bounds(
        &mut self,
        err: &mut Diag<'_>,
        source: PathSource<'_>,
        res: Option<Res>,
        span: Span,
        base_error: &BaseError,
    ) -> bool {
        let is_macro =
            base_error.span.from_expansion() && base_error.span.desugaring_kind().is_none();
        let mut fallback = false;

        if let (
            PathSource::Trait(AliasPossibility::Maybe),
            Some(Res::Def(DefKind::Struct | DefKind::Enum | DefKind::Union, _)),
            false,
        ) = (source, res, is_macro)
        {
            if let Some(bounds @ [first_bound, .., last_bound]) =
                self.diag_metadata.current_trait_object
            {
                fallback = true;
                let spans: Vec<Span> = bounds
                    .iter()
                    .map(|bound| bound.span())
                    .filter(|&sp| sp != base_error.span)
                    .collect();

                let start_span = first_bound.span();
                // `end_span` is the end of the poly trait ref (Foo + 'baz + Bar><)
                let end_span = last_bound.span();
                // `last_bound_span` is the last bound of the poly trait ref (Foo + >'baz< + Bar)
                let last_bound_span = spans.last().cloned().unwrap();
                let mut multi_span: MultiSpan = spans.clone().into();
                for sp in spans {
                    let msg = if sp == last_bound_span {
                        format!(
                            "...because of {these} bound{s}",
                            these = pluralize!("this", bounds.len() - 1),
                            s = pluralize!(bounds.len() - 1),
                        )
                    } else {
                        String::new()
                    };
                    multi_span.push_span_label(sp, msg);
                }
                multi_span.push_span_label(base_error.span, "expected this type to be a trait...");
                err.span_help(
                    multi_span,
                    "`+` is used to constrain a \"trait object\" type with lifetimes or \
                        auto-traits; structs and enums can't be bound in that way",
                );
                if bounds.iter().all(|bound| match bound {
                    ast::GenericBound::Outlives(_) => true,
                    ast::GenericBound::Trait(tr, _) => tr.span == base_error.span,
                }) {
                    let mut sugg = vec![];
                    if base_error.span != start_span {
                        sugg.push((start_span.until(base_error.span), String::new()));
                    }
                    if base_error.span != end_span {
                        sugg.push((base_error.span.shrink_to_hi().to(end_span), String::new()));
                    }

                    err.multipart_suggestion(
                        "if you meant to use a type and not a trait here, remove the bounds",
                        sugg,
                        Applicability::MaybeIncorrect,
                    );
                }
            }
        }

        fallback |= self.restrict_assoc_type_in_where_clause(span, err);
        fallback
    }

    fn suggest_typo(
        &mut self,
        err: &mut Diag<'_>,
        source: PathSource<'_>,
        path: &[Segment],
        following_seg: Option<&Segment>,
        span: Span,
        base_error: &BaseError,
    ) -> bool {
        let is_expected = &|res| source.is_expected(res);
        let ident_span = path.last().map_or(span, |ident| ident.ident.span);
        let typo_sugg =
            self.lookup_typo_candidate(path, following_seg, source.namespace(), is_expected);
        let mut fallback = false;
        let typo_sugg = typo_sugg.to_opt_suggestion();
        if !self.r.add_typo_suggestion(err, typo_sugg, ident_span) {
            fallback = true;
            match self.diag_metadata.current_let_binding {
                Some((pat_sp, Some(ty_sp), None))
                    if ty_sp.contains(base_error.span) && base_error.could_be_expr =>
                {
                    err.span_suggestion_short(
                        pat_sp.between(ty_sp),
                        "use `=` if you meant to assign",
                        " = ",
                        Applicability::MaybeIncorrect,
                    );
                }
                _ => {}
            }

            // If the trait has a single item (which wasn't matched by the algorithm), suggest it
            let suggestion = self.get_single_associated_item(path, &source, is_expected);
            if !self.r.add_typo_suggestion(err, suggestion, ident_span) {
                fallback = !self.let_binding_suggestion(err, ident_span);
            }
        }
        fallback
    }

    fn suggest_shadowed(
        &mut self,
        err: &mut Diag<'_>,
        source: PathSource<'_>,
        path: &[Segment],
        following_seg: Option<&Segment>,
        span: Span,
    ) -> bool {
        let is_expected = &|res| source.is_expected(res);
        let typo_sugg =
            self.lookup_typo_candidate(path, following_seg, source.namespace(), is_expected);
        let is_in_same_file = &|sp1, sp2| {
            let source_map = self.r.tcx.sess.source_map();
            let file1 = source_map.span_to_filename(sp1);
            let file2 = source_map.span_to_filename(sp2);
            file1 == file2
        };
        // print 'you might have meant' if the candidate is (1) is a shadowed name with
        // accessible definition and (2) either defined in the same crate as the typo
        // (could be in a different file) or introduced in the same file as the typo
        // (could belong to a different crate)
        if let TypoCandidate::Shadowed(res, Some(sugg_span)) = typo_sugg
            && res.opt_def_id().is_some_and(|id| id.is_local() || is_in_same_file(span, sugg_span))
        {
            err.span_label(
                sugg_span,
                format!("you might have meant to refer to this {}", res.descr()),
            );
            return true;
        }
        false
    }

    fn err_code_special_cases(
        &mut self,
        err: &mut Diag<'_>,
        source: PathSource<'_>,
        path: &[Segment],
        span: Span,
    ) {
        if let Some(err_code) = err.code {
            if err_code == E0425 {
                for label_rib in &self.label_ribs {
                    for (label_ident, node_id) in &label_rib.bindings {
                        let ident = path.last().unwrap().ident;
                        if format!("'{ident}") == label_ident.to_string() {
                            err.span_label(label_ident.span, "a label with a similar name exists");
                            if let PathSource::Expr(Some(Expr {
                                kind: ExprKind::Break(None, Some(_)),
                                ..
                            })) = source
                            {
                                err.span_suggestion(
                                    span,
                                    "use the similarly named label",
                                    label_ident.name,
                                    Applicability::MaybeIncorrect,
                                );
                                // Do not lint against unused label when we suggest them.
                                self.diag_metadata.unused_labels.remove(node_id);
                            }
                        }
                    }
                }
            } else if err_code == E0412 {
                if let Some(correct) = Self::likely_rust_type(path) {
                    err.span_suggestion(
                        span,
                        "perhaps you intended to use this type",
                        correct,
                        Applicability::MaybeIncorrect,
                    );
                }
            }
        }
    }

    /// Emit special messages for unresolved `Self` and `self`.
    fn suggest_self_ty(
        &mut self,
        err: &mut Diag<'_>,
        source: PathSource<'_>,
        path: &[Segment],
        span: Span,
    ) -> bool {
        if !is_self_type(path, source.namespace()) {
            return false;
        }
        err.code(E0411);
        err.span_label(span, "`Self` is only available in impls, traits, and type definitions");
        if let Some(item_kind) = self.diag_metadata.current_item {
            if !item_kind.ident.span.is_dummy() {
                err.span_label(
                    item_kind.ident.span,
                    format!(
                        "`Self` not allowed in {} {}",
                        item_kind.kind.article(),
                        item_kind.kind.descr()
                    ),
                );
            }
        }
        true
    }

    fn suggest_self_value(
        &mut self,
        err: &mut Diag<'_>,
        source: PathSource<'_>,
        path: &[Segment],
        span: Span,
    ) -> bool {
        if !is_self_value(path, source.namespace()) {
            return false;
        }

        debug!("smart_resolve_path_fragment: E0424, source={:?}", source);
        err.code(E0424);
        err.span_label(
            span,
            match source {
                PathSource::Pat => {
                    "`self` value is a keyword and may not be bound to variables or shadowed"
                }
                _ => "`self` value is a keyword only available in methods with a `self` parameter",
            },
        );
        let is_assoc_fn = self.self_type_is_available();
        if let Some((fn_kind, span)) = &self.diag_metadata.current_function {
            // The current function has a `self` parameter, but we were unable to resolve
            // a reference to `self`. This can only happen if the `self` identifier we
            // are resolving came from a different hygiene context.
            if fn_kind.decl().inputs.get(0).is_some_and(|p| p.is_self()) {
                err.span_label(*span, "this function has a `self` parameter, but a macro invocation can only access identifiers it receives from parameters");
            } else {
                let doesnt = if is_assoc_fn {
                    let (span, sugg) = fn_kind
                        .decl()
                        .inputs
                        .get(0)
                        .map(|p| (p.span.shrink_to_lo(), "&self, "))
                        .unwrap_or_else(|| {
                            // Try to look for the "(" after the function name, if possible.
                            // This avoids placing the suggestion into the visibility specifier.
                            let span = fn_kind
                                .ident()
                                .map_or(*span, |ident| span.with_lo(ident.span.hi()));
                            (
                                self.r
                                    .tcx
                                    .sess
                                    .source_map()
                                    .span_through_char(span, '(')
                                    .shrink_to_hi(),
                                "&self",
                            )
                        });
                    err.span_suggestion_verbose(
                        span,
                        "add a `self` receiver parameter to make the associated `fn` a method",
                        sugg,
                        Applicability::MaybeIncorrect,
                    );
                    "doesn't"
                } else {
                    "can't"
                };
                if let Some(ident) = fn_kind.ident() {
                    err.span_label(
                        ident.span,
                        format!("this function {doesnt} have a `self` parameter"),
                    );
                }
            }
        } else if let Some(item_kind) = self.diag_metadata.current_item {
            err.span_label(
                item_kind.ident.span,
                format!(
                    "`self` not allowed in {} {}",
                    item_kind.kind.article(),
                    item_kind.kind.descr()
                ),
            );
        }
        true
    }

    fn suggest_at_operator_in_slice_pat_with_range(
        &mut self,
        err: &mut Diag<'_>,
        path: &[Segment],
    ) {
        let Some(pat) = self.diag_metadata.current_pat else { return };
        let (bound, side, range) = match &pat.kind {
            ast::PatKind::Range(Some(bound), None, range) => (bound, Side::Start, range),
            ast::PatKind::Range(None, Some(bound), range) => (bound, Side::End, range),
            _ => return,
        };
        if let ExprKind::Path(None, range_path) = &bound.kind
            && let [segment] = &range_path.segments[..]
            && let [s] = path
            && segment.ident == s.ident
            && segment.ident.span.eq_ctxt(range.span)
        {
            // We've encountered `[first, rest..]` (#88404) or `[first, ..rest]` (#120591)
            // where the user might have meant `[first, rest @ ..]`.
            let (span, snippet) = match side {
                Side::Start => (segment.ident.span.between(range.span), " @ ".into()),
                Side::End => (range.span.to(segment.ident.span), format!("{} @ ..", segment.ident)),
            };
            err.subdiagnostic(
                self.r.dcx(),
                errors::UnexpectedResUseAtOpInSlicePatWithRangeSugg {
                    span,
                    ident: segment.ident,
                    snippet,
                },
            );
        }

        enum Side {
            Start,
            End,
        }
    }

    fn suggest_swapping_misplaced_self_ty_and_trait(
        &mut self,
        err: &mut Diag<'_>,
        source: PathSource<'_>,
        res: Option<Res>,
        span: Span,
    ) {
        if let Some((trait_ref, self_ty)) =
            self.diag_metadata.currently_processing_impl_trait.clone()
            && let TyKind::Path(_, self_ty_path) = &self_ty.kind
            && let PathResult::Module(ModuleOrUniformRoot::Module(module)) =
                self.resolve_path(&Segment::from_path(self_ty_path), Some(TypeNS), None)
            && let ModuleKind::Def(DefKind::Trait, ..) = module.kind
            && trait_ref.path.span == span
            && let PathSource::Trait(_) = source
            && let Some(Res::Def(DefKind::Struct | DefKind::Enum | DefKind::Union, _)) = res
            && let Ok(self_ty_str) = self.r.tcx.sess.source_map().span_to_snippet(self_ty.span)
            && let Ok(trait_ref_str) =
                self.r.tcx.sess.source_map().span_to_snippet(trait_ref.path.span)
        {
            err.multipart_suggestion(
                    "`impl` items mention the trait being implemented first and the type it is being implemented for second",
                    vec![(trait_ref.path.span, self_ty_str), (self_ty.span, trait_ref_str)],
                    Applicability::MaybeIncorrect,
                );
        }
    }

    fn suggest_bare_struct_literal(&mut self, err: &mut Diag<'_>) {
        if let Some(span) = self.diag_metadata.current_block_could_be_bare_struct_literal {
            err.multipart_suggestion(
                "you might have meant to write a `struct` literal",
                vec![
                    (span.shrink_to_lo(), "{ SomeStruct ".to_string()),
                    (span.shrink_to_hi(), "}".to_string()),
                ],
                Applicability::HasPlaceholders,
            );
        }
    }

    fn suggest_changing_type_to_const_param(
        &mut self,
        err: &mut Diag<'_>,
        res: Option<Res>,
        source: PathSource<'_>,
        span: Span,
    ) {
        let PathSource::Trait(_) = source else { return };

        // We don't include `DefKind::Str` and `DefKind::AssocTy` as they can't be reached here anyway.
        let applicability = match res {
            Some(Res::PrimTy(PrimTy::Int(_) | PrimTy::Uint(_) | PrimTy::Bool | PrimTy::Char)) => {
                Applicability::MachineApplicable
            }
            // FIXME(const_generics): Add `DefKind::TyParam` and `SelfTyParam` once we support generic
            // const generics. Of course, `Struct` and `Enum` may contain ty params, too, but the
            // benefits of including them here outweighs the small number of false positives.
            Some(Res::Def(DefKind::Struct | DefKind::Enum, _))
                if self.r.tcx.features().adt_const_params =>
            {
                Applicability::MaybeIncorrect
            }
            _ => return,
        };

        let Some(item) = self.diag_metadata.current_item else { return };
        let Some(generics) = item.kind.generics() else { return };

        let param = generics.params.iter().find_map(|param| {
            // Only consider type params with exactly one trait bound.
            if let [bound] = &*param.bounds
                && let ast::GenericBound::Trait(tref, ast::TraitBoundModifiers::NONE) = bound
                && tref.span == span
                && param.ident.span.eq_ctxt(span)
            {
                Some(param.ident.span)
            } else {
                None
            }
        });

        if let Some(param) = param {
            err.subdiagnostic(
                self.r.dcx(),
                errors::UnexpectedResChangeTyToConstParamSugg {
                    span: param.shrink_to_lo(),
                    applicability,
                },
            );
        }
    }

    fn suggest_pattern_match_with_let(
        &mut self,
        err: &mut Diag<'_>,
        source: PathSource<'_>,
        span: Span,
    ) -> bool {
        if let PathSource::Expr(_) = source
            && let Some(Expr { span: expr_span, kind: ExprKind::Assign(lhs, _, _), .. }) =
                self.diag_metadata.in_if_condition
        {
            // Icky heuristic so we don't suggest:
            // `if (i + 2) = 2` => `if let (i + 2) = 2` (approximately pattern)
            // `if 2 = i` => `if let 2 = i` (lhs needs to contain error span)
            if lhs.is_approximately_pattern() && lhs.span.contains(span) {
                err.span_suggestion_verbose(
                    expr_span.shrink_to_lo(),
                    "you might have meant to use pattern matching",
                    "let ",
                    Applicability::MaybeIncorrect,
                );
                return true;
            }
        }
        false
    }

    fn get_single_associated_item(
        &mut self,
        path: &[Segment],
        source: &PathSource<'_>,
        filter_fn: &impl Fn(Res) -> bool,
    ) -> Option<TypoSuggestion> {
        if let crate::PathSource::TraitItem(_) = source {
            let mod_path = &path[..path.len() - 1];
            if let PathResult::Module(ModuleOrUniformRoot::Module(module)) =
                self.resolve_path(mod_path, None, None)
            {
                let resolutions = self.r.resolutions(module).borrow();
                let targets: Vec<_> =
                    resolutions
                        .iter()
                        .filter_map(|(key, resolution)| {
                            resolution.borrow().binding.map(|binding| binding.res()).and_then(
                                |res| if filter_fn(res) { Some((key, res)) } else { None },
                            )
                        })
                        .collect();
                if targets.len() == 1 {
                    let target = targets[0];
                    return Some(TypoSuggestion::single_item_from_ident(target.0.ident, target.1));
                }
            }
        }
        None
    }

    /// Given `where <T as Bar>::Baz: String`, suggest `where T: Bar<Baz = String>`.
    fn restrict_assoc_type_in_where_clause(&mut self, span: Span, err: &mut Diag<'_>) -> bool {
        // Detect that we are actually in a `where` predicate.
        let (bounded_ty, bounds, where_span) =
            if let Some(ast::WherePredicate::BoundPredicate(ast::WhereBoundPredicate {
                bounded_ty,
                bound_generic_params,
                bounds,
                span,
            })) = self.diag_metadata.current_where_predicate
            {
                if !bound_generic_params.is_empty() {
                    return false;
                }
                (bounded_ty, bounds, span)
            } else {
                return false;
            };

        // Confirm that the target is an associated type.
        let (ty, _, path) = if let ast::TyKind::Path(Some(qself), path) = &bounded_ty.kind {
            // use this to verify that ident is a type param.
            let Some(partial_res) = self.r.partial_res_map.get(&bounded_ty.id) else {
                return false;
            };
            if !matches!(
                partial_res.full_res(),
                Some(hir::def::Res::Def(hir::def::DefKind::AssocTy, _))
            ) {
                return false;
            }
            (&qself.ty, qself.position, path)
        } else {
            return false;
        };

        let peeled_ty = ty.peel_refs();
        if let ast::TyKind::Path(None, type_param_path) = &peeled_ty.kind {
            // Confirm that the `SelfTy` is a type parameter.
            let Some(partial_res) = self.r.partial_res_map.get(&peeled_ty.id) else {
                return false;
            };
            if !matches!(
                partial_res.full_res(),
                Some(hir::def::Res::Def(hir::def::DefKind::TyParam, _))
            ) {
                return false;
            }
            if let (
                [ast::PathSegment { args: None, .. }],
                [ast::GenericBound::Trait(poly_trait_ref, ast::TraitBoundModifiers::NONE)],
            ) = (&type_param_path.segments[..], &bounds[..])
            {
                if let [ast::PathSegment { ident, args: None, .. }] =
                    &poly_trait_ref.trait_ref.path.segments[..]
                {
                    if ident.span == span {
                        let Some(new_where_bound_predicate) =
                            mk_where_bound_predicate(path, poly_trait_ref, ty)
                        else {
                            return false;
                        };
                        err.span_suggestion_verbose(
                            *where_span,
                            format!("constrain the associated type to `{ident}`"),
                            where_bound_predicate_to_string(&new_where_bound_predicate),
                            Applicability::MaybeIncorrect,
                        );
                    }
                    return true;
                }
            }
        }
        false
    }

    /// Check if the source is call expression and the first argument is `self`. If true,
    /// return the span of whole call and the span for all arguments expect the first one (`self`).
    fn call_has_self_arg(&self, source: PathSource<'_>) -> Option<(Span, Option<Span>)> {
        let mut has_self_arg = None;
        if let PathSource::Expr(Some(parent)) = source
            && let ExprKind::Call(_, args) = &parent.kind
            && !args.is_empty()
        {
            let mut expr_kind = &args[0].kind;
            loop {
                match expr_kind {
                    ExprKind::Path(_, arg_name) if arg_name.segments.len() == 1 => {
                        if arg_name.segments[0].ident.name == kw::SelfLower {
                            let call_span = parent.span;
                            let tail_args_span = if args.len() > 1 {
                                Some(Span::new(
                                    args[1].span.lo(),
                                    args.last().unwrap().span.hi(),
                                    call_span.ctxt(),
                                    None,
                                ))
                            } else {
                                None
                            };
                            has_self_arg = Some((call_span, tail_args_span));
                        }
                        break;
                    }
                    ExprKind::AddrOf(_, _, expr) => expr_kind = &expr.kind,
                    _ => break,
                }
            }
        }
        has_self_arg
    }

    fn followed_by_brace(&self, span: Span) -> (bool, Option<Span>) {
        // HACK(estebank): find a better way to figure out that this was a
        // parser issue where a struct literal is being used on an expression
        // where a brace being opened means a block is being started. Look
        // ahead for the next text to see if `span` is followed by a `{`.
        let sm = self.r.tcx.sess.source_map();
        if let Some(followed_brace_span) = sm.span_look_ahead(span, "{", Some(50)) {
            // In case this could be a struct literal that needs to be surrounded
            // by parentheses, find the appropriate span.
            let close_brace_span = sm.span_look_ahead(followed_brace_span, "}", Some(50));
            let closing_brace = close_brace_span.map(|sp| span.to(sp));
            (true, closing_brace)
        } else {
            (false, None)
        }
    }

    /// Provides context-dependent help for errors reported by the `smart_resolve_path_fragment`
    /// function.
    /// Returns `true` if able to provide context-dependent help.
    fn smart_resolve_context_dependent_help(
        &mut self,
        err: &mut Diag<'_>,
        span: Span,
        source: PathSource<'_>,
        path: &[Segment],
        res: Res,
        path_str: &str,
        fallback_label: &str,
    ) -> bool {
        let ns = source.namespace();
        let is_expected = &|res| source.is_expected(res);

        let path_sep = |this: &mut Self, err: &mut Diag<'_>, expr: &Expr, kind: DefKind| {
            const MESSAGE: &str = "use the path separator to refer to an item";

            let (lhs_span, rhs_span) = match &expr.kind {
                ExprKind::Field(base, ident) => (base.span, ident.span),
                ExprKind::MethodCall(box MethodCall { receiver, span, .. }) => {
                    (receiver.span, *span)
                }
                _ => return false,
            };

            if lhs_span.eq_ctxt(rhs_span) {
                err.span_suggestion(
                    lhs_span.between(rhs_span),
                    MESSAGE,
                    "::",
                    Applicability::MaybeIncorrect,
                );
                true
            } else if kind == DefKind::Struct
                && let Some(lhs_source_span) = lhs_span.find_ancestor_inside(expr.span)
                && let Ok(snippet) = this.r.tcx.sess.source_map().span_to_snippet(lhs_source_span)
            {
                // The LHS is a type that originates from a macro call.
                // We have to add angle brackets around it.

                err.span_suggestion_verbose(
                    lhs_source_span.until(rhs_span),
                    MESSAGE,
                    format!("<{snippet}>::"),
                    Applicability::MaybeIncorrect,
                );
                true
            } else {
                // Either we were unable to obtain the source span / the snippet or
                // the LHS originates from a macro call and it is not a type and thus
                // there is no way to replace `.` with `::` and still somehow suggest
                // valid Rust code.

                false
            }
        };

        let find_span = |source: &PathSource<'_>, err: &mut Diag<'_>| {
            match source {
                PathSource::Expr(Some(Expr { span, kind: ExprKind::Call(_, _), .. }))
                | PathSource::TupleStruct(span, _) => {
                    // We want the main underline to cover the suggested code as well for
                    // cleaner output.
                    err.span(*span);
                    *span
                }
                _ => span,
            }
        };

        let mut bad_struct_syntax_suggestion = |this: &mut Self, def_id: DefId| {
            let (followed_by_brace, closing_brace) = this.followed_by_brace(span);

            match source {
                PathSource::Expr(Some(
                    parent @ Expr { kind: ExprKind::Field(..) | ExprKind::MethodCall(..), .. },
                )) if path_sep(this, err, parent, DefKind::Struct) => {}
                PathSource::Expr(
                    None
                    | Some(Expr {
                        kind:
                            ExprKind::Path(..)
                            | ExprKind::Binary(..)
                            | ExprKind::Unary(..)
                            | ExprKind::If(..)
                            | ExprKind::While(..)
                            | ExprKind::ForLoop { .. }
                            | ExprKind::Match(..),
                        ..
                    }),
                ) if followed_by_brace => {
                    if let Some(sp) = closing_brace {
                        err.span_label(span, fallback_label.to_string());
                        err.multipart_suggestion(
                            "surround the struct literal with parentheses",
                            vec![
                                (sp.shrink_to_lo(), "(".to_string()),
                                (sp.shrink_to_hi(), ")".to_string()),
                            ],
                            Applicability::MaybeIncorrect,
                        );
                    } else {
                        err.span_label(
                            span, // Note the parentheses surrounding the suggestion below
                            format!(
                                "you might want to surround a struct literal with parentheses: \
                                 `({path_str} {{ /* fields */ }})`?"
                            ),
                        );
                    }
                }
                PathSource::Expr(_) | PathSource::TupleStruct(..) | PathSource::Pat => {
                    let span = find_span(&source, err);
                    err.span_label(this.r.def_span(def_id), format!("`{path_str}` defined here"));

                    let (tail, descr, applicability, old_fields) = match source {
                        PathSource::Pat => ("", "pattern", Applicability::MachineApplicable, None),
                        PathSource::TupleStruct(_, args) => (
                            "",
                            "pattern",
                            Applicability::MachineApplicable,
                            Some(
                                args.iter()
                                    .map(|a| this.r.tcx.sess.source_map().span_to_snippet(*a).ok())
                                    .collect::<Vec<Option<String>>>(),
                            ),
                        ),
                        _ => (": val", "literal", Applicability::HasPlaceholders, None),
                    };

                    if !this.has_private_fields(def_id) {
                        // If the fields of the type are private, we shouldn't be suggesting using
                        // the struct literal syntax at all, as that will cause a subsequent error.
                        let field_ids = this.r.field_def_ids(def_id);
                        let (fields, applicability) = match field_ids {
                            Some(field_ids) => {
                                let fields = field_ids.iter().map(|&id| this.r.tcx.item_name(id));

                                let fields = if let Some(old_fields) = old_fields {
                                    fields
                                        .enumerate()
                                        .map(|(idx, new)| (new, old_fields.get(idx)))
                                        .map(|(new, old)| {
                                            let new = new.to_ident_string();
                                            if let Some(Some(old)) = old
                                                && new != *old
                                            {
                                                format!("{new}: {old}")
                                            } else {
                                                new
                                            }
                                        })
                                        .collect::<Vec<String>>()
                                } else {
                                    fields.map(|f| format!("{f}{tail}")).collect::<Vec<String>>()
                                };

                                (fields.join(", "), applicability)
                            }
                            None => ("/* fields */".to_string(), Applicability::HasPlaceholders),
                        };
                        let pad = match field_ids {
                            Some([]) => "",
                            _ => " ",
                        };
                        err.span_suggestion(
                            span,
                            format!("use struct {descr} syntax instead"),
                            format!("{path_str} {{{pad}{fields}{pad}}}"),
                            applicability,
                        );
                    }
                    if let PathSource::Expr(Some(Expr {
                        kind: ExprKind::Call(path, ref args),
                        span: call_span,
                        ..
                    })) = source
                    {
                        this.suggest_alternative_construction_methods(
                            def_id,
                            err,
                            path.span,
                            *call_span,
                            &args[..],
                        );
                    }
                }
                _ => {
                    err.span_label(span, fallback_label.to_string());
                }
            }
        };

        match (res, source) {
            (
                Res::Def(DefKind::Macro(MacroKind::Bang), def_id),
                PathSource::Expr(Some(Expr {
                    kind: ExprKind::Index(..) | ExprKind::Call(..), ..
                }))
                | PathSource::Struct,
            ) => {
                // Don't suggest macro if it's unstable.
                let suggestable = def_id.is_local()
                    || self.r.tcx.lookup_stability(def_id).map_or(true, |s| s.is_stable());

                err.span_label(span, fallback_label.to_string());

                // Don't suggest `!` for a macro invocation if there are generic args
                if path
                    .last()
                    .is_some_and(|segment| !segment.has_generic_args && !segment.has_lifetime_args)
                    && suggestable
                {
                    err.span_suggestion_verbose(
                        span.shrink_to_hi(),
                        "use `!` to invoke the macro",
                        "!",
                        Applicability::MaybeIncorrect,
                    );
                }

                if path_str == "try" && span.is_rust_2015() {
                    err.note("if you want the `try` keyword, you need Rust 2018 or later");
                }
            }
            (Res::Def(DefKind::Macro(MacroKind::Bang), _), _) => {
                err.span_label(span, fallback_label.to_string());
            }
            (Res::Def(DefKind::TyAlias, def_id), PathSource::Trait(_)) => {
                err.span_label(span, "type aliases cannot be used as traits");
                if self.r.tcx.sess.is_nightly_build() {
                    let msg = "you might have meant to use `#![feature(trait_alias)]` instead of a \
                               `type` alias";
                    let span = self.r.def_span(def_id);
                    if let Ok(snip) = self.r.tcx.sess.source_map().span_to_snippet(span) {
                        // The span contains a type alias so we should be able to
                        // replace `type` with `trait`.
                        let snip = snip.replacen("type", "trait", 1);
                        err.span_suggestion(span, msg, snip, Applicability::MaybeIncorrect);
                    } else {
                        err.span_help(span, msg);
                    }
                }
            }
            (
                Res::Def(kind @ (DefKind::Mod | DefKind::Trait), _),
                PathSource::Expr(Some(parent)),
            ) => {
                if !path_sep(self, err, parent, kind) {
                    return false;
                }
            }
            (
                Res::Def(DefKind::Enum, def_id),
                PathSource::TupleStruct(..) | PathSource::Expr(..),
            ) => {
                self.suggest_using_enum_variant(err, source, def_id, span);
            }
            (Res::Def(DefKind::Struct, def_id), source) if ns == ValueNS => {
                let struct_ctor = match def_id.as_local() {
                    Some(def_id) => self.r.struct_constructors.get(&def_id).cloned(),
                    None => {
                        let ctor = self.r.cstore().ctor_untracked(def_id);
                        ctor.map(|(ctor_kind, ctor_def_id)| {
                            let ctor_res =
                                Res::Def(DefKind::Ctor(CtorOf::Struct, ctor_kind), ctor_def_id);
                            let ctor_vis = self.r.tcx.visibility(ctor_def_id);
                            let field_visibilities = self
                                .r
                                .tcx
                                .associated_item_def_ids(def_id)
                                .iter()
                                .map(|field_id| self.r.tcx.visibility(field_id))
                                .collect();
                            (ctor_res, ctor_vis, field_visibilities)
                        })
                    }
                };

                let (ctor_def, ctor_vis, fields) = if let Some(struct_ctor) = struct_ctor {
                    if let PathSource::Expr(Some(parent)) = source {
                        if let ExprKind::Field(..) | ExprKind::MethodCall(..) = parent.kind {
                            bad_struct_syntax_suggestion(self, def_id);
                            return true;
                        }
                    }
                    struct_ctor
                } else {
                    bad_struct_syntax_suggestion(self, def_id);
                    return true;
                };

                let is_accessible = self.r.is_accessible_from(ctor_vis, self.parent_scope.module);
                if !is_expected(ctor_def) || is_accessible {
                    return true;
                }

                let field_spans = match source {
                    // e.g. `if let Enum::TupleVariant(field1, field2) = _`
                    PathSource::TupleStruct(_, pattern_spans) => {
                        err.primary_message(
                            "cannot match against a tuple struct which contains private fields",
                        );

                        // Use spans of the tuple struct pattern.
                        Some(Vec::from(pattern_spans))
                    }
                    // e.g. `let _ = Enum::TupleVariant(field1, field2);`
                    PathSource::Expr(Some(Expr {
                        kind: ExprKind::Call(path, ref args),
                        span: call_span,
                        ..
                    })) => {
                        err.primary_message(
                            "cannot initialize a tuple struct which contains private fields",
                        );
                        self.suggest_alternative_construction_methods(
                            def_id,
                            err,
                            path.span,
                            *call_span,
                            &args[..],
                        );
                        // Use spans of the tuple struct definition.
                        self.r.field_def_ids(def_id).map(|field_ids| {
                            field_ids
                                .iter()
                                .map(|&field_id| self.r.def_span(field_id))
                                .collect::<Vec<_>>()
                        })
                    }
                    _ => None,
                };

                if let Some(spans) =
                    field_spans.filter(|spans| spans.len() > 0 && fields.len() == spans.len())
                {
                    let non_visible_spans: Vec<Span> = iter::zip(&fields, &spans)
                        .filter(|(vis, _)| {
                            !self.r.is_accessible_from(**vis, self.parent_scope.module)
                        })
                        .map(|(_, span)| *span)
                        .collect();

                    if non_visible_spans.len() > 0 {
                        if let Some(fields) = self.r.field_visibility_spans.get(&def_id) {
                            err.multipart_suggestion_verbose(
                                format!(
                                    "consider making the field{} publicly accessible",
                                    pluralize!(fields.len())
                                ),
                                fields.iter().map(|span| (*span, "pub ".to_string())).collect(),
                                Applicability::MaybeIncorrect,
                            );
                        }

                        let mut m: MultiSpan = non_visible_spans.clone().into();
                        non_visible_spans
                            .into_iter()
                            .for_each(|s| m.push_span_label(s, "private field"));
                        err.span_note(m, "constructor is not visible here due to private fields");
                    }

                    return true;
                }

                err.span_label(span, "constructor is not visible here due to private fields");
            }
            (Res::Def(DefKind::Union | DefKind::Variant, def_id), _) if ns == ValueNS => {
                bad_struct_syntax_suggestion(self, def_id);
            }
            (Res::Def(DefKind::Ctor(_, CtorKind::Const), def_id), _) if ns == ValueNS => {
                match source {
                    PathSource::Expr(_) | PathSource::TupleStruct(..) | PathSource::Pat => {
                        let span = find_span(&source, err);
                        err.span_label(
                            self.r.def_span(def_id),
                            format!("`{path_str}` defined here"),
                        );
                        err.span_suggestion(
                            span,
                            "use this syntax instead",
                            path_str,
                            Applicability::MaybeIncorrect,
                        );
                    }
                    _ => return false,
                }
            }
            (Res::Def(DefKind::Ctor(_, CtorKind::Fn), ctor_def_id), _) if ns == ValueNS => {
                let def_id = self.r.tcx.parent(ctor_def_id);
                err.span_label(self.r.def_span(def_id), format!("`{path_str}` defined here"));
                let fields = self.r.field_def_ids(def_id).map_or_else(
                    || "/* fields */".to_string(),
                    |field_ids| vec!["_"; field_ids.len()].join(", "),
                );
                err.span_suggestion(
                    span,
                    "use the tuple variant pattern syntax instead",
                    format!("{path_str}({fields})"),
                    Applicability::HasPlaceholders,
                );
            }
            (Res::SelfTyParam { .. } | Res::SelfTyAlias { .. }, _) if ns == ValueNS => {
                err.span_label(span, fallback_label.to_string());
                err.note("can't use `Self` as a constructor, you must use the implemented struct");
            }
            (Res::Def(DefKind::TyAlias | DefKind::AssocTy, _), _) if ns == ValueNS => {
                err.note("can't use a type alias as a constructor");
            }
            _ => return false,
        }
        true
    }

    fn suggest_alternative_construction_methods(
        &mut self,
        def_id: DefId,
        err: &mut Diag<'_>,
        path_span: Span,
        call_span: Span,
        args: &[P<Expr>],
    ) {
        if def_id.is_local() {
            // Doing analysis on local `DefId`s would cause infinite recursion.
            return;
        }
        let Ok(impls) = self.r.tcx.inherent_impls(def_id) else { return };
        // Look at all the associated functions without receivers in the type's
        // inherent impls to look for builders that return `Self`
        let mut items = impls
            .iter()
            .flat_map(|i| self.r.tcx.associated_items(i).in_definition_order())
            // Only assoc fn with no receivers.
            .filter(|item| matches!(item.kind, ty::AssocKind::Fn) && !item.fn_has_self_parameter)
            .filter_map(|item| {
                // Only assoc fns that return `Self`
                let fn_sig = self.r.tcx.fn_sig(item.def_id).skip_binder();
                // Don't normalize the return type, because that can cause cycle errors.
                let ret_ty = fn_sig.output().skip_binder();
                let ty::Adt(def, _args) = ret_ty.kind() else {
                    return None;
                };
                let input_len = fn_sig.inputs().skip_binder().len();
                if def.did() != def_id {
                    return None;
                }
                let order = !item.name.as_str().starts_with("new");
                Some((order, item.name, input_len))
            })
            .collect::<Vec<_>>();
        items.sort_by_key(|(order, _, _)| *order);
        let suggestion = |name, args| {
            format!(
                "::{name}({})",
                std::iter::repeat("_").take(args).collect::<Vec<_>>().join(", ")
            )
        };
        match &items[..] {
            [] => {}
            [(_, name, len)] if *len == args.len() => {
                err.span_suggestion_verbose(
                    path_span.shrink_to_hi(),
                    format!("you might have meant to use the `{name}` associated function",),
                    format!("::{name}"),
                    Applicability::MaybeIncorrect,
                );
            }
            [(_, name, len)] => {
                err.span_suggestion_verbose(
                    path_span.shrink_to_hi().with_hi(call_span.hi()),
                    format!("you might have meant to use the `{name}` associated function",),
                    suggestion(name, *len),
                    Applicability::MaybeIncorrect,
                );
            }
            _ => {
                err.span_suggestions_with_style(
                    path_span.shrink_to_hi().with_hi(call_span.hi()),
                    "you might have meant to use an associated function to build this type",
                    items.iter().map(|(_, name, len)| suggestion(name, *len)),
                    Applicability::MaybeIncorrect,
                    SuggestionStyle::ShowAlways,
                );
            }
        }
        // We'd ideally use `type_implements_trait` but don't have access to
        // the trait solver here. We can't use `get_diagnostic_item` or
        // `all_traits` in resolve either. So instead we abuse the import
        // suggestion machinery to get `std::default::Default` and perform some
        // checks to confirm that we got *only* that trait. We then see if the
        // Adt we have has a direct implementation of `Default`. If so, we
        // provide a structured suggestion.
        let default_trait = self
            .r
            .lookup_import_candidates(
                Ident::with_dummy_span(sym::Default),
                Namespace::TypeNS,
                &self.parent_scope,
                &|res: Res| matches!(res, Res::Def(DefKind::Trait, _)),
            )
            .iter()
            .filter_map(|candidate| candidate.did)
            .find(|did| {
                self.r
                    .tcx
                    .get_attrs(*did, sym::rustc_diagnostic_item)
                    .any(|attr| attr.value_str() == Some(sym::Default))
            });
        let Some(default_trait) = default_trait else {
            return;
        };
        if self
            .r
            .extern_crate_map
            .iter()
            // FIXME: This doesn't include impls like `impl Default for String`.
            .flat_map(|(_, crate_)| self.r.tcx.implementations_of_trait((*crate_, default_trait)))
            .filter_map(|(_, simplified_self_ty)| *simplified_self_ty)
            .filter_map(|simplified_self_ty| match simplified_self_ty {
                SimplifiedType::Adt(did) => Some(did),
                _ => None,
            })
            .any(|did| did == def_id)
        {
            err.multipart_suggestion(
                "consider using the `Default` trait",
                vec![
                    (path_span.shrink_to_lo(), "<".to_string()),
                    (
                        path_span.shrink_to_hi().with_hi(call_span.hi()),
                        " as std::default::Default>::default()".to_string(),
                    ),
                ],
                Applicability::MaybeIncorrect,
            );
        }
    }

    fn has_private_fields(&self, def_id: DefId) -> bool {
        let fields = match def_id.as_local() {
            Some(def_id) => self.r.struct_constructors.get(&def_id).cloned().map(|(_, _, f)| f),
            None => Some(
                self.r
                    .tcx
                    .associated_item_def_ids(def_id)
                    .iter()
                    .map(|field_id| self.r.tcx.visibility(field_id))
                    .collect(),
            ),
        };

        fields.is_some_and(|fields| {
            fields.iter().any(|vis| !self.r.is_accessible_from(*vis, self.parent_scope.module))
        })
    }

    /// Given the target `ident` and `kind`, search for the similarly named associated item
    /// in `self.current_trait_ref`.
    pub(crate) fn find_similarly_named_assoc_item(
        &mut self,
        ident: Symbol,
        kind: &AssocItemKind,
    ) -> Option<Symbol> {
        let (module, _) = self.current_trait_ref.as_ref()?;
        if ident == kw::Underscore {
            // We do nothing for `_`.
            return None;
        }

        let resolutions = self.r.resolutions(*module);
        let targets = resolutions
            .borrow()
            .iter()
            .filter_map(|(key, res)| res.borrow().binding.map(|binding| (key, binding.res())))
            .filter(|(_, res)| match (kind, res) {
                (AssocItemKind::Const(..), Res::Def(DefKind::AssocConst, _)) => true,
                (AssocItemKind::Fn(_), Res::Def(DefKind::AssocFn, _)) => true,
                (AssocItemKind::Type(..), Res::Def(DefKind::AssocTy, _)) => true,
                (AssocItemKind::Delegation(_), Res::Def(DefKind::AssocFn, _)) => true,
                _ => false,
            })
            .map(|(key, _)| key.ident.name)
            .collect::<Vec<_>>();

        find_best_match_for_name(&targets, ident, None)
    }

    fn lookup_assoc_candidate<FilterFn>(
        &mut self,
        ident: Ident,
        ns: Namespace,
        filter_fn: FilterFn,
        called: bool,
    ) -> Option<AssocSuggestion>
    where
        FilterFn: Fn(Res) -> bool,
    {
        fn extract_node_id(t: &Ty) -> Option<NodeId> {
            match t.kind {
                TyKind::Path(None, _) => Some(t.id),
                TyKind::Ref(_, ref mut_ty) => extract_node_id(&mut_ty.ty),
                // This doesn't handle the remaining `Ty` variants as they are not
                // that commonly the self_type, it might be interesting to provide
                // support for those in future.
                _ => None,
            }
        }
        // Fields are generally expected in the same contexts as locals.
        if filter_fn(Res::Local(ast::DUMMY_NODE_ID)) {
            if let Some(node_id) =
                self.diag_metadata.current_self_type.as_ref().and_then(extract_node_id)
            {
                // Look for a field with the same name in the current self_type.
                if let Some(resolution) = self.r.partial_res_map.get(&node_id) {
                    if let Some(Res::Def(DefKind::Struct | DefKind::Union, did)) =
                        resolution.full_res()
                    {
                        if let Some(field_ids) = self.r.field_def_ids(did) {
                            if let Some(field_id) = field_ids
                                .iter()
                                .find(|&&field_id| ident.name == self.r.tcx.item_name(field_id))
                            {
                                return Some(AssocSuggestion::Field(self.r.def_span(*field_id)));
                            }
                        }
                    }
                }
            }
        }

        if let Some(items) = self.diag_metadata.current_trait_assoc_items {
            for assoc_item in items {
                if assoc_item.ident == ident {
                    return Some(match &assoc_item.kind {
                        ast::AssocItemKind::Const(..) => AssocSuggestion::AssocConst,
                        ast::AssocItemKind::Fn(box ast::Fn { sig, .. }) if sig.decl.has_self() => {
                            AssocSuggestion::MethodWithSelf { called }
                        }
                        ast::AssocItemKind::Fn(..) => AssocSuggestion::AssocFn { called },
                        ast::AssocItemKind::Type(..) => AssocSuggestion::AssocType,
                        ast::AssocItemKind::Delegation(..)
                            if self.r.has_self.contains(&self.r.local_def_id(assoc_item.id)) =>
                        {
                            AssocSuggestion::MethodWithSelf { called }
                        }
                        ast::AssocItemKind::Delegation(..) => AssocSuggestion::AssocFn { called },
                        ast::AssocItemKind::MacCall(_) => continue,
                    });
                }
            }
        }

        // Look for associated items in the current trait.
        if let Some((module, _)) = self.current_trait_ref {
            if let Ok(binding) = self.r.maybe_resolve_ident_in_module(
                ModuleOrUniformRoot::Module(module),
                ident,
                ns,
                &self.parent_scope,
            ) {
                let res = binding.res();
                if filter_fn(res) {
                    let def_id = res.def_id();
                    let has_self = match def_id.as_local() {
                        Some(def_id) => self.r.has_self.contains(&def_id),
                        None => self
                            .r
                            .tcx
                            .fn_arg_names(def_id)
                            .first()
                            .is_some_and(|ident| ident.name == kw::SelfLower),
                    };
                    if has_self {
                        return Some(AssocSuggestion::MethodWithSelf { called });
                    } else {
                        match res {
                            Res::Def(DefKind::AssocFn, _) => {
                                return Some(AssocSuggestion::AssocFn { called });
                            }
                            Res::Def(DefKind::AssocConst, _) => {
                                return Some(AssocSuggestion::AssocConst);
                            }
                            Res::Def(DefKind::AssocTy, _) => {
                                return Some(AssocSuggestion::AssocType);
                            }
                            _ => {}
                        }
                    }
                }
            }
        }

        None
    }

    fn lookup_typo_candidate(
        &mut self,
        path: &[Segment],
        following_seg: Option<&Segment>,
        ns: Namespace,
        filter_fn: &impl Fn(Res) -> bool,
    ) -> TypoCandidate {
        let mut names = Vec::new();
        if path.len() == 1 {
            let mut ctxt = path.last().unwrap().ident.span.ctxt();

            // Search in lexical scope.
            // Walk backwards up the ribs in scope and collect candidates.
            for rib in self.ribs[ns].iter().rev() {
                let rib_ctxt = if rib.kind.contains_params() {
                    ctxt.normalize_to_macros_2_0()
                } else {
                    ctxt.normalize_to_macro_rules()
                };

                // Locals and type parameters
                for (ident, &res) in &rib.bindings {
                    if filter_fn(res) && ident.span.ctxt() == rib_ctxt {
                        names.push(TypoSuggestion::typo_from_ident(*ident, res));
                    }
                }

                if let RibKind::MacroDefinition(def) = rib.kind
                    && def == self.r.macro_def(ctxt)
                {
                    // If an invocation of this macro created `ident`, give up on `ident`
                    // and switch to `ident`'s source from the macro definition.
                    ctxt.remove_mark();
                    continue;
                }

                // Items in scope
                if let RibKind::Module(module) = rib.kind {
                    // Items from this module
                    self.r.add_module_candidates(module, &mut names, &filter_fn, Some(ctxt));

                    if let ModuleKind::Block = module.kind {
                        // We can see through blocks
                    } else {
                        // Items from the prelude
                        if !module.no_implicit_prelude {
                            let extern_prelude = self.r.extern_prelude.clone();
                            names.extend(extern_prelude.iter().flat_map(|(ident, _)| {
                                self.r
                                    .crate_loader(|c| c.maybe_process_path_extern(ident.name))
                                    .and_then(|crate_id| {
                                        let crate_mod =
                                            Res::Def(DefKind::Mod, crate_id.as_def_id());

                                        filter_fn(crate_mod).then(|| {
                                            TypoSuggestion::typo_from_ident(*ident, crate_mod)
                                        })
                                    })
                            }));

                            if let Some(prelude) = self.r.prelude {
                                self.r.add_module_candidates(prelude, &mut names, &filter_fn, None);
                            }
                        }
                        break;
                    }
                }
            }
            // Add primitive types to the mix
            if filter_fn(Res::PrimTy(PrimTy::Bool)) {
                names.extend(PrimTy::ALL.iter().map(|prim_ty| {
                    TypoSuggestion::typo_from_name(prim_ty.name(), Res::PrimTy(*prim_ty))
                }))
            }
        } else {
            // Search in module.
            let mod_path = &path[..path.len() - 1];
            if let PathResult::Module(ModuleOrUniformRoot::Module(module)) =
                self.resolve_path(mod_path, Some(TypeNS), None)
            {
                self.r.add_module_candidates(module, &mut names, &filter_fn, None);
            }
        }

        // if next_seg is present, let's filter everything that does not continue the path
        if let Some(following_seg) = following_seg {
            names.retain(|suggestion| match suggestion.res {
                Res::Def(DefKind::Struct | DefKind::Enum | DefKind::Union, _) => {
                    // FIXME: this is not totally accurate, but mostly works
                    suggestion.candidate != following_seg.ident.name
                }
                Res::Def(DefKind::Mod, def_id) => self.r.get_module(def_id).map_or_else(
                    || false,
                    |module| {
                        self.r
                            .resolutions(module)
                            .borrow()
                            .iter()
                            .any(|(key, _)| key.ident.name == following_seg.ident.name)
                    },
                ),
                _ => true,
            });
        }
        let name = path[path.len() - 1].ident.name;
        // Make sure error reporting is deterministic.
        names.sort_by(|a, b| a.candidate.as_str().cmp(b.candidate.as_str()));

        match find_best_match_for_name(
            &names.iter().map(|suggestion| suggestion.candidate).collect::<Vec<Symbol>>(),
            name,
            None,
        ) {
            Some(found) => {
                let Some(sugg) = names.into_iter().find(|suggestion| suggestion.candidate == found)
                else {
                    return TypoCandidate::None;
                };
                if found == name {
                    TypoCandidate::Shadowed(sugg.res, sugg.span)
                } else {
                    TypoCandidate::Typo(sugg)
                }
            }
            _ => TypoCandidate::None,
        }
    }

    // Returns the name of the Rust type approximately corresponding to
    // a type name in another programming language.
    fn likely_rust_type(path: &[Segment]) -> Option<Symbol> {
        let name = path[path.len() - 1].ident.as_str();
        // Common Java types
        Some(match name {
            "byte" => sym::u8, // In Java, bytes are signed, but in practice one almost always wants unsigned bytes.
            "short" => sym::i16,
            "Bool" => sym::bool,
            "Boolean" => sym::bool,
            "boolean" => sym::bool,
            "int" => sym::i32,
            "long" => sym::i64,
            "float" => sym::f32,
            "double" => sym::f64,
            _ => return None,
        })
    }

    // try to give a suggestion for this pattern: `name = blah`, which is common in other languages
    // suggest `let name = blah` to introduce a new binding
    fn let_binding_suggestion(&mut self, err: &mut Diag<'_>, ident_span: Span) -> bool {
        if let Some(Expr { kind: ExprKind::Assign(lhs, ..), .. }) = self.diag_metadata.in_assignment
            && let ast::ExprKind::Path(None, ref path) = lhs.kind
        {
            if !ident_span.from_expansion() {
                let (span, text) = match path.segments.first() {
                    Some(seg) if let Some(name) = seg.ident.as_str().strip_prefix("let") => {
                        // a special case for #117894
                        let name = name.strip_prefix('_').unwrap_or(name);
                        (ident_span, format!("let {name}"))
                    }
                    _ => (ident_span.shrink_to_lo(), "let ".to_string()),
                };

                err.span_suggestion_verbose(
                    span,
                    "you might have meant to introduce a new binding",
                    text,
                    Applicability::MaybeIncorrect,
                );
                return true;
            }
        }
        false
    }

    fn find_module(&mut self, def_id: DefId) -> Option<(Module<'a>, ImportSuggestion)> {
        let mut result = None;
        let mut seen_modules = FxHashSet::default();
        let root_did = self.r.graph_root.def_id();
        let mut worklist = vec![(
            self.r.graph_root,
            ThinVec::new(),
            root_did.is_local() || !self.r.tcx.is_doc_hidden(root_did),
        )];

        while let Some((in_module, path_segments, doc_visible)) = worklist.pop() {
            // abort if the module is already found
            if result.is_some() {
                break;
            }

            in_module.for_each_child(self.r, |r, ident, _, name_binding| {
                // abort if the module is already found or if name_binding is private external
                if result.is_some() || !name_binding.vis.is_visible_locally() {
                    return;
                }
                if let Some(module) = name_binding.module() {
                    // form the path
                    let mut path_segments = path_segments.clone();
                    path_segments.push(ast::PathSegment::from_ident(ident));
                    let module_def_id = module.def_id();
                    let doc_visible = doc_visible
                        && (module_def_id.is_local() || !r.tcx.is_doc_hidden(module_def_id));
                    if module_def_id == def_id {
                        let path =
                            Path { span: name_binding.span, segments: path_segments, tokens: None };
                        result = Some((
                            module,
                            ImportSuggestion {
                                did: Some(def_id),
                                descr: "module",
                                path,
                                accessible: true,
                                doc_visible,
                                note: None,
                                via_import: false,
                            },
                        ));
                    } else {
                        // add the module to the lookup
                        if seen_modules.insert(module_def_id) {
                            worklist.push((module, path_segments, doc_visible));
                        }
                    }
                }
            });
        }

        result
    }

    fn collect_enum_ctors(&mut self, def_id: DefId) -> Option<Vec<(Path, DefId, CtorKind)>> {
        self.find_module(def_id).map(|(enum_module, enum_import_suggestion)| {
            let mut variants = Vec::new();
            enum_module.for_each_child(self.r, |_, ident, _, name_binding| {
                if let Res::Def(DefKind::Ctor(CtorOf::Variant, kind), def_id) = name_binding.res() {
                    let mut segms = enum_import_suggestion.path.segments.clone();
                    segms.push(ast::PathSegment::from_ident(ident));
                    let path = Path { span: name_binding.span, segments: segms, tokens: None };
                    variants.push((path, def_id, kind));
                }
            });
            variants
        })
    }

    /// Adds a suggestion for using an enum's variant when an enum is used instead.
    fn suggest_using_enum_variant(
        &mut self,
        err: &mut Diag<'_>,
        source: PathSource<'_>,
        def_id: DefId,
        span: Span,
    ) {
        let Some(variants) = self.collect_enum_ctors(def_id) else {
            err.note("you might have meant to use one of the enum's variants");
            return;
        };

        let suggest_only_tuple_variants =
            matches!(source, PathSource::TupleStruct(..)) || source.is_call();
        if suggest_only_tuple_variants {
            // Suggest only tuple variants regardless of whether they have fields and do not
            // suggest path with added parentheses.
            let mut suggestable_variants = variants
                .iter()
                .filter(|(.., kind)| *kind == CtorKind::Fn)
                .map(|(variant, ..)| path_names_to_string(variant))
                .collect::<Vec<_>>();
            suggestable_variants.sort();

            let non_suggestable_variant_count = variants.len() - suggestable_variants.len();

            let source_msg = if source.is_call() {
                "to construct"
            } else if matches!(source, PathSource::TupleStruct(..)) {
                "to match against"
            } else {
                unreachable!()
            };

            if !suggestable_variants.is_empty() {
                let msg = if non_suggestable_variant_count == 0 && suggestable_variants.len() == 1 {
                    format!("try {source_msg} the enum's variant")
                } else {
                    format!("try {source_msg} one of the enum's variants")
                };

                err.span_suggestions(
                    span,
                    msg,
                    suggestable_variants,
                    Applicability::MaybeIncorrect,
                );
            }

            // If the enum has no tuple variants..
            if non_suggestable_variant_count == variants.len() {
                err.help(format!("the enum has no tuple variants {source_msg}"));
            }

            // If there are also non-tuple variants..
            if non_suggestable_variant_count == 1 {
                err.help(format!("you might have meant {source_msg} the enum's non-tuple variant"));
            } else if non_suggestable_variant_count >= 1 {
                err.help(format!(
                    "you might have meant {source_msg} one of the enum's non-tuple variants"
                ));
            }
        } else {
            let needs_placeholder = |ctor_def_id: DefId, kind: CtorKind| {
                let def_id = self.r.tcx.parent(ctor_def_id);
                match kind {
                    CtorKind::Const => false,
                    CtorKind::Fn => {
                        !self.r.field_def_ids(def_id).is_some_and(|field_ids| field_ids.is_empty())
                    }
                }
            };

            let mut suggestable_variants = variants
                .iter()
                .filter(|(_, def_id, kind)| !needs_placeholder(*def_id, *kind))
                .map(|(variant, _, kind)| (path_names_to_string(variant), kind))
                .map(|(variant, kind)| match kind {
                    CtorKind::Const => variant,
                    CtorKind::Fn => format!("({variant}())"),
                })
                .collect::<Vec<_>>();
            suggestable_variants.sort();
            let no_suggestable_variant = suggestable_variants.is_empty();

            if !no_suggestable_variant {
                let msg = if suggestable_variants.len() == 1 {
                    "you might have meant to use the following enum variant"
                } else {
                    "you might have meant to use one of the following enum variants"
                };

                err.span_suggestions(
                    span,
                    msg,
                    suggestable_variants,
                    Applicability::MaybeIncorrect,
                );
            }

            let mut suggestable_variants_with_placeholders = variants
                .iter()
                .filter(|(_, def_id, kind)| needs_placeholder(*def_id, *kind))
                .map(|(variant, _, kind)| (path_names_to_string(variant), kind))
                .filter_map(|(variant, kind)| match kind {
                    CtorKind::Fn => Some(format!("({variant}(/* fields */))")),
                    _ => None,
                })
                .collect::<Vec<_>>();
            suggestable_variants_with_placeholders.sort();

            if !suggestable_variants_with_placeholders.is_empty() {
                let msg =
                    match (no_suggestable_variant, suggestable_variants_with_placeholders.len()) {
                        (true, 1) => "the following enum variant is available",
                        (true, _) => "the following enum variants are available",
                        (false, 1) => "alternatively, the following enum variant is available",
                        (false, _) => {
                            "alternatively, the following enum variants are also available"
                        }
                    };

                err.span_suggestions(
                    span,
                    msg,
                    suggestable_variants_with_placeholders,
                    Applicability::HasPlaceholders,
                );
            }
        };

        if def_id.is_local() {
            err.span_note(self.r.def_span(def_id), "the enum is defined here");
        }
    }

    pub(crate) fn suggest_adding_generic_parameter(
        &self,
        path: &[Segment],
        source: PathSource<'_>,
    ) -> Option<(Span, &'static str, String, Applicability)> {
        let (ident, span) = match path {
            [segment]
                if !segment.has_generic_args
                    && segment.ident.name != kw::SelfUpper
                    && segment.ident.name != kw::Dyn =>
            {
                (segment.ident.to_string(), segment.ident.span)
            }
            _ => return None,
        };
        let mut iter = ident.chars().map(|c| c.is_uppercase());
        let single_uppercase_char =
            matches!(iter.next(), Some(true)) && matches!(iter.next(), None);
        if !self.diag_metadata.currently_processing_generic_args && !single_uppercase_char {
            return None;
        }
        match (self.diag_metadata.current_item, single_uppercase_char, self.diag_metadata.currently_processing_generic_args) {
            (Some(Item { kind: ItemKind::Fn(..), ident, .. }), _, _) if ident.name == sym::main => {
                // Ignore `fn main()` as we don't want to suggest `fn main<T>()`
            }
            (
                Some(Item {
                    kind:
                        kind @ ItemKind::Fn(..)
                        | kind @ ItemKind::Enum(..)
                        | kind @ ItemKind::Struct(..)
                        | kind @ ItemKind::Union(..),
                    ..
                }),
                true, _
            )
            // Without the 2nd `true`, we'd suggest `impl <T>` for `impl T` when a type `T` isn't found
            | (Some(Item { kind: kind @ ItemKind::Impl(..), .. }), true, true)
            | (Some(Item { kind, .. }), false, _) => {
                if let Some(generics) = kind.generics() {
                    if span.overlaps(generics.span) {
                        // Avoid the following:
                        // error[E0405]: cannot find trait `A` in this scope
                        //  --> $DIR/typo-suggestion-named-underscore.rs:CC:LL
                        //   |
                        // L | fn foo<T: A>(x: T) {} // Shouldn't suggest underscore
                        //   |           ^- help: you might be missing a type parameter: `, A`
                        //   |           |
                        //   |           not found in this scope
                        return None;
                    }

                    let (msg, sugg) = match source {
                        PathSource::Type => ("you might be missing a type parameter", ident),
                        PathSource::Expr(_) => ("you might be missing a const parameter", format!("const {ident}: /* Type */")),
                        _ => return None,
                    };
                    let (span, sugg) = if let [.., param] = &generics.params[..] {
                        let span = if let [.., bound] = &param.bounds[..] {
                            bound.span()
                        } else if let GenericParam {
                            kind: GenericParamKind::Const { ty, kw_span: _, default  }, ..
                        } = param {
                            default.as_ref().map(|def| def.value.span).unwrap_or(ty.span)
                        } else {
                            param.ident.span
                        };
                        (span, format!(", {sugg}"))
                    } else {
                        (generics.span, format!("<{sugg}>"))
                    };
                    // Do not suggest if this is coming from macro expansion.
                    if span.can_be_used_for_suggestions() {
                        return Some((
                            span.shrink_to_hi(),
                            msg,
                            sugg,
                            Applicability::MaybeIncorrect,
                        ));
                    }
                }
            }
            _ => {}
        }
        None
    }

    /// Given the target `label`, search the `rib_index`th label rib for similarly named labels,
    /// optionally returning the closest match and whether it is reachable.
    pub(crate) fn suggestion_for_label_in_rib(
        &self,
        rib_index: usize,
        label: Ident,
    ) -> Option<LabelSuggestion> {
        // Are ribs from this `rib_index` within scope?
        let within_scope = self.is_label_valid_from_rib(rib_index);

        let rib = &self.label_ribs[rib_index];
        let names = rib
            .bindings
            .iter()
            .filter(|(id, _)| id.span.eq_ctxt(label.span))
            .map(|(id, _)| id.name)
            .collect::<Vec<Symbol>>();

        find_best_match_for_name(&names, label.name, None).map(|symbol| {
            // Upon finding a similar name, get the ident that it was from - the span
            // contained within helps make a useful diagnostic. In addition, determine
            // whether this candidate is within scope.
            let (ident, _) = rib.bindings.iter().find(|(ident, _)| ident.name == symbol).unwrap();
            (*ident, within_scope)
        })
    }

    pub(crate) fn maybe_report_lifetime_uses(
        &mut self,
        generics_span: Span,
        params: &[ast::GenericParam],
    ) {
        for (param_index, param) in params.iter().enumerate() {
            let GenericParamKind::Lifetime = param.kind else { continue };

            let def_id = self.r.local_def_id(param.id);

            let use_set = self.lifetime_uses.remove(&def_id);
            debug!(
                "Use set for {:?}({:?} at {:?}) is {:?}",
                def_id, param.ident, param.ident.span, use_set
            );

            let deletion_span = || {
                if params.len() == 1 {
                    // if sole lifetime, remove the entire `<>` brackets
                    Some(generics_span)
                } else if param_index == 0 {
                    // if removing within `<>` brackets, we also want to
                    // delete a leading or trailing comma as appropriate
                    match (
                        param.span().find_ancestor_inside(generics_span),
                        params[param_index + 1].span().find_ancestor_inside(generics_span),
                    ) {
                        (Some(param_span), Some(next_param_span)) => {
                            Some(param_span.to(next_param_span.shrink_to_lo()))
                        }
                        _ => None,
                    }
                } else {
                    // if removing within `<>` brackets, we also want to
                    // delete a leading or trailing comma as appropriate
                    match (
                        param.span().find_ancestor_inside(generics_span),
                        params[param_index - 1].span().find_ancestor_inside(generics_span),
                    ) {
                        (Some(param_span), Some(prev_param_span)) => {
                            Some(prev_param_span.shrink_to_hi().to(param_span))
                        }
                        _ => None,
                    }
                }
            };
            match use_set {
                Some(LifetimeUseSet::Many) => {}
                Some(LifetimeUseSet::One { use_span, use_ctxt }) => {
                    debug!(?param.ident, ?param.ident.span, ?use_span);

                    let elidable = matches!(use_ctxt, LifetimeCtxt::Ref);
                    let deletion_span =
                        if param.bounds.is_empty() { deletion_span() } else { None };

                    self.r.lint_buffer.buffer_lint_with_diagnostic(
                        lint::builtin::SINGLE_USE_LIFETIMES,
                        param.id,
                        param.ident.span,
                        format!("lifetime parameter `{}` only used once", param.ident),
                        lint::BuiltinLintDiag::SingleUseLifetime {
                            param_span: param.ident.span,
                            use_span: Some((use_span, elidable)),
                            deletion_span,
                        },
                    );
                }
                None => {
                    debug!(?param.ident, ?param.ident.span);
                    let deletion_span = deletion_span();

                    // if the lifetime originates from expanded code, we won't be able to remove it #104432
                    if deletion_span.is_some_and(|sp| !sp.in_derive_expansion()) {
                        self.r.lint_buffer.buffer_lint_with_diagnostic(
                            lint::builtin::UNUSED_LIFETIMES,
                            param.id,
                            param.ident.span,
                            format!("lifetime parameter `{}` never used", param.ident),
                            lint::BuiltinLintDiag::SingleUseLifetime {
                                param_span: param.ident.span,
                                use_span: None,
                                deletion_span,
                            },
                        );
                    }
                }
            }
        }
    }

    pub(crate) fn emit_undeclared_lifetime_error(
        &self,
        lifetime_ref: &ast::Lifetime,
        outer_lifetime_ref: Option<Ident>,
    ) {
        debug_assert_ne!(lifetime_ref.ident.name, kw::UnderscoreLifetime);
        let mut err = if let Some(outer) = outer_lifetime_ref {
            struct_span_code_err!(
                self.r.dcx(),
                lifetime_ref.ident.span,
                E0401,
                "can't use generic parameters from outer item",
            )
            .with_span_label(lifetime_ref.ident.span, "use of generic parameter from outer item")
            .with_span_label(outer.span, "lifetime parameter from outer item")
        } else {
            struct_span_code_err!(
                self.r.dcx(),
                lifetime_ref.ident.span,
                E0261,
                "use of undeclared lifetime name `{}`",
                lifetime_ref.ident
            )
            .with_span_label(lifetime_ref.ident.span, "undeclared lifetime")
        };
        self.suggest_introducing_lifetime(
            &mut err,
            Some(lifetime_ref.ident.name.as_str()),
            |err, _, span, message, suggestion| {
                err.span_suggestion(span, message, suggestion, Applicability::MaybeIncorrect);
                true
            },
        );
        err.emit();
    }

    fn suggest_introducing_lifetime(
        &self,
        err: &mut Diag<'_>,
        name: Option<&str>,
        suggest: impl Fn(&mut Diag<'_>, bool, Span, Cow<'static, str>, String) -> bool,
    ) {
        let mut suggest_note = true;
        for rib in self.lifetime_ribs.iter().rev() {
            let mut should_continue = true;
            match rib.kind {
                LifetimeRibKind::Generics { binder: _, span, kind } => {
                    // Avoid suggesting placing lifetime parameters on constant items unless the relevant
                    // feature is enabled. Suggest the parent item as a possible location if applicable.
                    if let LifetimeBinderKind::ConstItem = kind
                        && !self.r.tcx().features().generic_const_items
                    {
                        continue;
                    }

                    if !span.can_be_used_for_suggestions()
                        && suggest_note
                        && let Some(name) = name
                    {
                        suggest_note = false; // Avoid displaying the same help multiple times.
                        err.span_label(
                            span,
                            format!(
                                "lifetime `{name}` is missing in item created through this procedural macro",
                            ),
                        );
                        continue;
                    }

                    let higher_ranked = matches!(
                        kind,
                        LifetimeBinderKind::BareFnType
                            | LifetimeBinderKind::PolyTrait
                            | LifetimeBinderKind::WhereBound
                    );
                    let (span, sugg) = if span.is_empty() {
                        let sugg = format!(
                            "{}<{}>{}",
                            if higher_ranked { "for" } else { "" },
                            name.unwrap_or("'a"),
                            if higher_ranked { " " } else { "" },
                        );
                        (span, sugg)
                    } else {
                        let span = self
                            .r
                            .tcx
                            .sess
                            .source_map()
                            .span_through_char(span, '<')
                            .shrink_to_hi();
                        let sugg = format!("{}, ", name.unwrap_or("'a"));
                        (span, sugg)
                    };
                    if higher_ranked {
                        let message = Cow::from(format!(
                            "consider making the {} lifetime-generic with a new `{}` lifetime",
                            kind.descr(),
                            name.unwrap_or("'a"),
                        ));
                        should_continue = suggest(err, true, span, message, sugg);
                        err.note_once(
                            "for more information on higher-ranked polymorphism, visit \
                             https://doc.rust-lang.org/nomicon/hrtb.html",
                        );
                    } else if let Some(name) = name {
                        let message =
                            Cow::from(format!("consider introducing lifetime `{name}` here"));
                        should_continue = suggest(err, false, span, message, sugg);
                    } else {
                        let message = Cow::from("consider introducing a named lifetime parameter");
                        should_continue = suggest(err, false, span, message, sugg);
                    }
                }
                LifetimeRibKind::Item | LifetimeRibKind::ConstParamTy => break,
                _ => {}
            }
            if !should_continue {
                break;
            }
        }
    }

    pub(crate) fn emit_non_static_lt_in_const_param_ty_error(&self, lifetime_ref: &ast::Lifetime) {
        self.r
            .dcx()
            .create_err(errors::ParamInTyOfConstParam {
                span: lifetime_ref.ident.span,
                name: lifetime_ref.ident.name,
                param_kind: Some(errors::ParamKindInTyOfConstParam::Lifetime),
            })
            .emit();
    }

    /// Non-static lifetimes are prohibited in anonymous constants under `min_const_generics`.
    /// This function will emit an error if `generic_const_exprs` is not enabled, the body identified by
    /// `body_id` is an anonymous constant and `lifetime_ref` is non-static.
    pub(crate) fn emit_forbidden_non_static_lifetime_error(
        &self,
        cause: NoConstantGenericsReason,
        lifetime_ref: &ast::Lifetime,
    ) {
        match cause {
            NoConstantGenericsReason::IsEnumDiscriminant => {
                self.r
                    .dcx()
                    .create_err(errors::ParamInEnumDiscriminant {
                        span: lifetime_ref.ident.span,
                        name: lifetime_ref.ident.name,
                        param_kind: errors::ParamKindInEnumDiscriminant::Lifetime,
                    })
                    .emit();
            }
            NoConstantGenericsReason::NonTrivialConstArg => {
                assert!(!self.r.tcx.features().generic_const_exprs);
                self.r
                    .dcx()
                    .create_err(errors::ParamInNonTrivialAnonConst {
                        span: lifetime_ref.ident.span,
                        name: lifetime_ref.ident.name,
                        param_kind: errors::ParamKindInNonTrivialAnonConst::Lifetime,
                        help: self
                            .r
                            .tcx
                            .sess
                            .is_nightly_build()
                            .then_some(errors::ParamInNonTrivialAnonConstHelp),
                    })
                    .emit();
            }
        }
    }

    pub(crate) fn report_missing_lifetime_specifiers(
        &mut self,
        lifetime_refs: Vec<MissingLifetime>,
        function_param_lifetimes: Option<(Vec<MissingLifetime>, Vec<ElisionFnParameter>)>,
    ) -> ErrorGuaranteed {
        let num_lifetimes: usize = lifetime_refs.iter().map(|lt| lt.count).sum();
        let spans: Vec<_> = lifetime_refs.iter().map(|lt| lt.span).collect();

        let mut err = struct_span_code_err!(
            self.r.dcx(),
            spans,
            E0106,
            "missing lifetime specifier{}",
            pluralize!(num_lifetimes)
        );
        self.add_missing_lifetime_specifiers_label(
            &mut err,
            lifetime_refs,
            function_param_lifetimes,
        );
        err.emit()
    }

    fn add_missing_lifetime_specifiers_label(
        &mut self,
        err: &mut Diag<'_>,
        lifetime_refs: Vec<MissingLifetime>,
        function_param_lifetimes: Option<(Vec<MissingLifetime>, Vec<ElisionFnParameter>)>,
    ) {
        for &lt in &lifetime_refs {
            err.span_label(
                lt.span,
                format!(
                    "expected {} lifetime parameter{}",
                    if lt.count == 1 { "named".to_string() } else { lt.count.to_string() },
                    pluralize!(lt.count),
                ),
            );
        }

        let mut in_scope_lifetimes: Vec<_> = self
            .lifetime_ribs
            .iter()
            .rev()
            .take_while(|rib| {
                !matches!(rib.kind, LifetimeRibKind::Item | LifetimeRibKind::ConstParamTy)
            })
            .flat_map(|rib| rib.bindings.iter())
            .map(|(&ident, &res)| (ident, res))
            .filter(|(ident, _)| ident.name != kw::UnderscoreLifetime)
            .collect();
        debug!(?in_scope_lifetimes);

        let mut maybe_static = false;
        debug!(?function_param_lifetimes);
        if let Some((param_lifetimes, params)) = &function_param_lifetimes {
            let elided_len = param_lifetimes.len();
            let num_params = params.len();

            let mut m = String::new();

            for (i, info) in params.iter().enumerate() {
                let ElisionFnParameter { ident, index, lifetime_count, span } = *info;
                debug_assert_ne!(lifetime_count, 0);

                err.span_label(span, "");

                if i != 0 {
                    if i + 1 < num_params {
                        m.push_str(", ");
                    } else if num_params == 2 {
                        m.push_str(" or ");
                    } else {
                        m.push_str(", or ");
                    }
                }

                let help_name = if let Some(ident) = ident {
                    format!("`{ident}`")
                } else {
                    format!("argument {}", index + 1)
                };

                if lifetime_count == 1 {
                    m.push_str(&help_name[..])
                } else {
                    m.push_str(&format!("one of {help_name}'s {lifetime_count} lifetimes")[..])
                }
            }

            if num_params == 0 {
                err.help(
                    "this function's return type contains a borrowed value, but there is no value \
                     for it to be borrowed from",
                );
                if in_scope_lifetimes.is_empty() {
                    maybe_static = true;
                    in_scope_lifetimes = vec![(
                        Ident::with_dummy_span(kw::StaticLifetime),
                        (DUMMY_NODE_ID, LifetimeRes::Static),
                    )];
                }
            } else if elided_len == 0 {
                err.help(
                    "this function's return type contains a borrowed value with an elided \
                     lifetime, but the lifetime cannot be derived from the arguments",
                );
                if in_scope_lifetimes.is_empty() {
                    maybe_static = true;
                    in_scope_lifetimes = vec![(
                        Ident::with_dummy_span(kw::StaticLifetime),
                        (DUMMY_NODE_ID, LifetimeRes::Static),
                    )];
                }
            } else if num_params == 1 {
                err.help(format!(
                    "this function's return type contains a borrowed value, but the signature does \
                     not say which {m} it is borrowed from",
                ));
            } else {
                err.help(format!(
                    "this function's return type contains a borrowed value, but the signature does \
                     not say whether it is borrowed from {m}",
                ));
            }
        }

        let existing_name = match &in_scope_lifetimes[..] {
            [] => Symbol::intern("'a"),
            [(existing, _)] => existing.name,
            _ => Symbol::intern("'lifetime"),
        };

        let mut spans_suggs: Vec<_> = Vec::new();
        let build_sugg = |lt: MissingLifetime| match lt.kind {
            MissingLifetimeKind::Underscore => {
                debug_assert_eq!(lt.count, 1);
                (lt.span, existing_name.to_string())
            }
            MissingLifetimeKind::Ampersand => {
                debug_assert_eq!(lt.count, 1);
                (lt.span.shrink_to_hi(), format!("{existing_name} "))
            }
            MissingLifetimeKind::Comma => {
                let sugg: String = std::iter::repeat([existing_name.as_str(), ", "])
                    .take(lt.count)
                    .flatten()
                    .collect();
                (lt.span.shrink_to_hi(), sugg)
            }
            MissingLifetimeKind::Brackets => {
                let sugg: String = std::iter::once("<")
                    .chain(
                        std::iter::repeat(existing_name.as_str()).take(lt.count).intersperse(", "),
                    )
                    .chain([">"])
                    .collect();
                (lt.span.shrink_to_hi(), sugg)
            }
        };
        for &lt in &lifetime_refs {
            spans_suggs.push(build_sugg(lt));
        }
        debug!(?spans_suggs);
        match in_scope_lifetimes.len() {
            0 => {
                if let Some((param_lifetimes, _)) = function_param_lifetimes {
                    for lt in param_lifetimes {
                        spans_suggs.push(build_sugg(lt))
                    }
                }
                self.suggest_introducing_lifetime(
                    err,
                    None,
                    |err, higher_ranked, span, message, intro_sugg| {
                        err.multipart_suggestion_verbose(
                            message,
                            std::iter::once((span, intro_sugg))
                                .chain(spans_suggs.iter().cloned())
                                .collect(),
                            Applicability::MaybeIncorrect,
                        );
                        higher_ranked
                    },
                );
            }
            1 => {
                let post = if maybe_static {
                    let owned = if let [lt] = &lifetime_refs[..]
                        && lt.kind != MissingLifetimeKind::Ampersand
                    {
                        ", or if you will only have owned values"
                    } else {
                        ""
                    };
                    format!(
                        ", but this is uncommon unless you're returning a borrowed value from a \
                         `const` or a `static`{owned}",
                    )
                } else {
                    String::new()
                };
                err.multipart_suggestion_verbose(
                    format!("consider using the `{existing_name}` lifetime{post}"),
                    spans_suggs,
                    Applicability::MaybeIncorrect,
                );
                if maybe_static {
                    // FIXME: what follows are general suggestions, but we'd want to perform some
                    // minimal flow analysis to provide more accurate suggestions. For example, if
                    // we identified that the return expression references only one argument, we
                    // would suggest borrowing only that argument, and we'd skip the prior
                    // "use `'static`" suggestion entirely.
                    if let [lt] = &lifetime_refs[..]
                        && (lt.kind == MissingLifetimeKind::Ampersand
                            || lt.kind == MissingLifetimeKind::Underscore)
                    {
                        let pre = if lt.kind == MissingLifetimeKind::Ampersand
                            && let Some((kind, _span)) = self.diag_metadata.current_function
                            && let FnKind::Fn(_, _, sig, _, _, _) = kind
                            && !sig.decl.inputs.is_empty()
                            && let sugg = sig
                                .decl
                                .inputs
                                .iter()
                                .filter_map(|param| {
                                    if param.ty.span.contains(lt.span) {
                                        // We don't want to suggest `fn elision(_: &fn() -> &i32)`
                                        // when we have `fn elision(_: fn() -> &i32)`
                                        None
                                    } else if let TyKind::CVarArgs = param.ty.kind {
                                        // Don't suggest `&...` for ffi fn with varargs
                                        None
                                    } else if let TyKind::ImplTrait(..) = &param.ty.kind {
                                        // We handle these in the next `else if` branch.
                                        None
                                    } else {
                                        Some((param.ty.span.shrink_to_lo(), "&".to_string()))
                                    }
                                })
                                .collect::<Vec<_>>()
                            && !sugg.is_empty()
                        {
                            let (the, s) = if sig.decl.inputs.len() == 1 {
                                ("the", "")
                            } else {
                                ("one of the", "s")
                            };
                            err.multipart_suggestion_verbose(
                                format!(
                                    "instead, you are more likely to want to change {the} \
                                     argument{s} to be borrowed...",
                                ),
                                sugg,
                                Applicability::MaybeIncorrect,
                            );
                            "...or alternatively, you might want"
                        } else if (lt.kind == MissingLifetimeKind::Ampersand
                            || lt.kind == MissingLifetimeKind::Underscore)
                            && let Some((kind, _span)) = self.diag_metadata.current_function
                            && let FnKind::Fn(_, _, sig, _, _, _) = kind
                            && let ast::FnRetTy::Ty(ret_ty) = &sig.decl.output
                            && !sig.decl.inputs.is_empty()
                            && let arg_refs = sig
                                .decl
                                .inputs
                                .iter()
                                .filter_map(|param| match &param.ty.kind {
                                    TyKind::ImplTrait(_, bounds) => Some(bounds),
                                    _ => None,
                                })
                                .flat_map(|bounds| bounds.into_iter())
                                .collect::<Vec<_>>()
                            && !arg_refs.is_empty()
                        {
                            // We have a situation like
                            // fn g(mut x: impl Iterator<Item = &()>) -> Option<&()>
                            // So we look at every ref in the trait bound. If there's any, we
                            // suggest
                            // fn g<'a>(mut x: impl Iterator<Item = &'a ()>) -> Option<&'a ()>
                            let mut lt_finder =
                                LifetimeFinder { lifetime: lt.span, found: None, seen: vec![] };
                            for bound in arg_refs {
                                if let ast::GenericBound::Trait(trait_ref, _) = bound {
                                    lt_finder.visit_trait_ref(&trait_ref.trait_ref);
                                }
                            }
                            lt_finder.visit_ty(ret_ty);
                            let spans_suggs: Vec<_> = lt_finder
                                .seen
                                .iter()
                                .filter_map(|ty| match &ty.kind {
                                    TyKind::Ref(_, mut_ty) => {
                                        let span = ty.span.with_hi(mut_ty.ty.span.lo());
                                        Some((span, "&'a ".to_string()))
                                    }
                                    _ => None,
                                })
                                .collect();
                            self.suggest_introducing_lifetime(
                                err,
                                None,
                                |err, higher_ranked, span, message, intro_sugg| {
                                    err.multipart_suggestion_verbose(
                                        message,
                                        std::iter::once((span, intro_sugg))
                                            .chain(spans_suggs.iter().cloned())
                                            .collect(),
                                        Applicability::MaybeIncorrect,
                                    );
                                    higher_ranked
                                },
                            );
                            "alternatively, you might want"
                        } else {
                            "instead, you are more likely to want"
                        };
                        let mut owned_sugg = lt.kind == MissingLifetimeKind::Ampersand;
                        let mut sugg = vec![(lt.span, String::new())];
                        if let Some((kind, _span)) = self.diag_metadata.current_function
                            && let FnKind::Fn(_, _, sig, _, _, _) = kind
                            && let ast::FnRetTy::Ty(ty) = &sig.decl.output
                        {
                            let mut lt_finder =
                                LifetimeFinder { lifetime: lt.span, found: None, seen: vec![] };
                            lt_finder.visit_ty(&ty);

                            if let [Ty { span, kind: TyKind::Ref(_, mut_ty), .. }] =
                                &lt_finder.seen[..]
                            {
                                // We might have a situation like
                                // fn g(mut x: impl Iterator<Item = &'_ ()>) -> Option<&'_ ()>
                                // but `lt.span` only points at `'_`, so to suggest `-> Option<()>`
                                // we need to find a more accurate span to end up with
                                // fn g<'a>(mut x: impl Iterator<Item = &'_ ()>) -> Option<()>
                                sugg = vec![(span.with_hi(mut_ty.ty.span.lo()), String::new())];
                                owned_sugg = true;
                            }
                            if let Some(ty) = lt_finder.found {
                                if let TyKind::Path(None, path) = &ty.kind {
                                    // Check if the path being borrowed is likely to be owned.
                                    let path: Vec<_> = Segment::from_path(path);
                                    match self.resolve_path(&path, Some(TypeNS), None) {
                                        PathResult::Module(ModuleOrUniformRoot::Module(module)) => {
                                            match module.res() {
                                                Some(Res::PrimTy(PrimTy::Str)) => {
                                                    // Don't suggest `-> str`, suggest `-> String`.
                                                    sugg = vec![(
                                                        lt.span.with_hi(ty.span.hi()),
                                                        "String".to_string(),
                                                    )];
                                                }
                                                Some(Res::PrimTy(..)) => {}
                                                Some(Res::Def(
                                                    DefKind::Struct
                                                    | DefKind::Union
                                                    | DefKind::Enum
                                                    | DefKind::ForeignTy
                                                    | DefKind::AssocTy
                                                    | DefKind::OpaqueTy
                                                    | DefKind::TyParam,
                                                    _,
                                                )) => {}
                                                _ => {
                                                    // Do not suggest in all other cases.
                                                    owned_sugg = false;
                                                }
                                            }
                                        }
                                        PathResult::NonModule(res) => {
                                            match res.base_res() {
                                                Res::PrimTy(PrimTy::Str) => {
                                                    // Don't suggest `-> str`, suggest `-> String`.
                                                    sugg = vec![(
                                                        lt.span.with_hi(ty.span.hi()),
                                                        "String".to_string(),
                                                    )];
                                                }
                                                Res::PrimTy(..) => {}
                                                Res::Def(
                                                    DefKind::Struct
                                                    | DefKind::Union
                                                    | DefKind::Enum
                                                    | DefKind::ForeignTy
                                                    | DefKind::AssocTy
                                                    | DefKind::OpaqueTy
                                                    | DefKind::TyParam,
                                                    _,
                                                ) => {}
                                                _ => {
                                                    // Do not suggest in all other cases.
                                                    owned_sugg = false;
                                                }
                                            }
                                        }
                                        _ => {
                                            // Do not suggest in all other cases.
                                            owned_sugg = false;
                                        }
                                    }
                                }
                                if let TyKind::Slice(inner_ty) = &ty.kind {
                                    // Don't suggest `-> [T]`, suggest `-> Vec<T>`.
                                    sugg = vec![
                                        (lt.span.with_hi(inner_ty.span.lo()), "Vec<".to_string()),
                                        (ty.span.with_lo(inner_ty.span.hi()), ">".to_string()),
                                    ];
                                }
                            }
                        }
                        if owned_sugg {
                            err.multipart_suggestion_verbose(
                                format!("{pre} to return an owned value"),
                                sugg,
                                Applicability::MaybeIncorrect,
                            );
                        }
                    }
                }

                // Record as using the suggested resolution.
                let (_, (_, res)) = in_scope_lifetimes[0];
                for &lt in &lifetime_refs {
                    self.r.lifetimes_res_map.insert(lt.id, res);
                }
            }
            _ => {
                let lifetime_spans: Vec<_> =
                    in_scope_lifetimes.iter().map(|(ident, _)| ident.span).collect();
                err.span_note(lifetime_spans, "these named lifetimes are available to use");

                if spans_suggs.len() > 0 {
                    // This happens when we have `Foo<T>` where we point at the space before `T`,
                    // but this can be confusing so we give a suggestion with placeholders.
                    err.multipart_suggestion_verbose(
                        "consider using one of the available lifetimes here",
                        spans_suggs,
                        Applicability::HasPlaceholders,
                    );
                }
            }
        }
    }
}

fn mk_where_bound_predicate(
    path: &Path,
    poly_trait_ref: &ast::PolyTraitRef,
    ty: &Ty,
) -> Option<ast::WhereBoundPredicate> {
    use rustc_span::DUMMY_SP;
    let modified_segments = {
        let mut segments = path.segments.clone();
        let [preceding @ .., second_last, last] = segments.as_mut_slice() else {
            return None;
        };
        let mut segments = ThinVec::from(preceding);

        let added_constraint = ast::AngleBracketedArg::Constraint(ast::AssocConstraint {
            id: DUMMY_NODE_ID,
            ident: last.ident,
            gen_args: None,
            kind: ast::AssocConstraintKind::Equality {
                term: ast::Term::Ty(ast::ptr::P(ast::Ty {
                    kind: ast::TyKind::Path(None, poly_trait_ref.trait_ref.path.clone()),
                    id: DUMMY_NODE_ID,
                    span: DUMMY_SP,
                    tokens: None,
                })),
            },
            span: DUMMY_SP,
        });

        match second_last.args.as_deref_mut() {
            Some(ast::GenericArgs::AngleBracketed(ast::AngleBracketedArgs { args, .. })) => {
                args.push(added_constraint);
            }
            Some(_) => return None,
            None => {
                second_last.args =
                    Some(ast::ptr::P(ast::GenericArgs::AngleBracketed(ast::AngleBracketedArgs {
                        args: ThinVec::from([added_constraint]),
                        span: DUMMY_SP,
                    })));
            }
        }

        segments.push(second_last.clone());
        segments
    };

    let new_where_bound_predicate = ast::WhereBoundPredicate {
        span: DUMMY_SP,
        bound_generic_params: ThinVec::new(),
        bounded_ty: ast::ptr::P(ty.clone()),
        bounds: vec![ast::GenericBound::Trait(
            ast::PolyTraitRef {
                bound_generic_params: ThinVec::new(),
                trait_ref: ast::TraitRef {
                    path: ast::Path { segments: modified_segments, span: DUMMY_SP, tokens: None },
                    ref_id: DUMMY_NODE_ID,
                },
                span: DUMMY_SP,
            },
            ast::TraitBoundModifiers::NONE,
        )],
    };

    Some(new_where_bound_predicate)
}

/// Report lifetime/lifetime shadowing as an error.
pub(super) fn signal_lifetime_shadowing(sess: &Session, orig: Ident, shadower: Ident) {
    struct_span_code_err!(
        sess.dcx(),
        shadower.span,
        E0496,
        "lifetime name `{}` shadows a lifetime name that is already in scope",
        orig.name,
    )
    .with_span_label(orig.span, "first declared here")
    .with_span_label(shadower.span, format!("lifetime `{}` already in scope", orig.name))
    .emit();
}

struct LifetimeFinder<'ast> {
    lifetime: Span,
    found: Option<&'ast Ty>,
    seen: Vec<&'ast Ty>,
}

impl<'ast> Visitor<'ast> for LifetimeFinder<'ast> {
    fn visit_ty(&mut self, t: &'ast Ty) {
        if let TyKind::Ref(_, mut_ty) = &t.kind {
            self.seen.push(t);
            if t.span.lo() == self.lifetime.lo() {
                self.found = Some(&mut_ty.ty);
            }
        }
        walk_ty(self, t)
    }
}

/// Shadowing involving a label is only a warning for historical reasons.
//FIXME: make this a proper lint.
pub(super) fn signal_label_shadowing(sess: &Session, orig: Span, shadower: Ident) {
    let name = shadower.name;
    let shadower = shadower.span;
    sess.dcx()
        .struct_span_warn(
            shadower,
            format!("label name `{name}` shadows a label name that is already in scope"),
        )
        .with_span_label(orig, "first declared here")
        .with_span_label(shadower, format!("label `{name}` already in scope"))
        .emit();
}