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
//! Util methods for [`rustc_middle::ty`]

#![allow(clippy::module_name_repetitions)]

use core::ops::ControlFlow;
use itertools::Itertools;
use rustc_ast::ast::Mutability;
use rustc_data_structures::fx::{FxHashMap, FxHashSet};
use rustc_hir as hir;
use rustc_hir::def::{CtorKind, CtorOf, DefKind, Res};
use rustc_hir::def_id::DefId;
use rustc_hir::{Expr, FnDecl, LangItem, TyKind, Unsafety};
use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
use rustc_infer::infer::TyCtxtInferExt;
use rustc_lint::LateContext;
use rustc_middle::mir::interpret::Scalar;
use rustc_middle::mir::ConstValue;
use rustc_middle::traits::EvaluationResult;
use rustc_middle::ty::layout::ValidityRequirement;
use rustc_middle::ty::{
    self, AdtDef, AliasTy, AssocKind, Binder, BoundRegion, FnSig, GenericArg, GenericArgKind, GenericArgsRef,
    GenericParamDefKind, IntTy, List, ParamEnv, Region, RegionKind, ToPredicate, TraitRef, Ty, TyCtxt,
    TypeSuperVisitable, TypeVisitable, TypeVisitableExt, TypeVisitor, UintTy, VariantDef, VariantDiscr,
};
use rustc_span::symbol::Ident;
use rustc_span::{sym, Span, Symbol, DUMMY_SP};
use rustc_target::abi::{Size, VariantIdx};
use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt as _;
use rustc_trait_selection::traits::query::normalize::QueryNormalizeExt;
use rustc_trait_selection::traits::{Obligation, ObligationCause};
use std::assert_matches::debug_assert_matches;
use std::iter;

use crate::{match_def_path, path_res};

mod type_certainty;
pub use type_certainty::expr_type_is_certain;

/// Checks if the given type implements copy.
pub fn is_copy<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
    ty.is_copy_modulo_regions(cx.tcx, cx.param_env)
}

/// This checks whether a given type is known to implement Debug.
pub fn has_debug_impl<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
    cx.tcx
        .get_diagnostic_item(sym::Debug)
        .map_or(false, |debug| implements_trait(cx, ty, debug, &[]))
}

/// Checks whether a type can be partially moved.
pub fn can_partially_move_ty<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
    if has_drop(cx, ty) || is_copy(cx, ty) {
        return false;
    }
    match ty.kind() {
        ty::Param(_) => false,
        ty::Adt(def, subs) => def.all_fields().any(|f| !is_copy(cx, f.ty(cx.tcx, subs))),
        _ => true,
    }
}

/// Walks into `ty` and returns `true` if any inner type is an instance of the given adt
/// constructor.
pub fn contains_adt_constructor<'tcx>(ty: Ty<'tcx>, adt: AdtDef<'tcx>) -> bool {
    ty.walk().any(|inner| match inner.unpack() {
        GenericArgKind::Type(inner_ty) => inner_ty.ty_adt_def() == Some(adt),
        GenericArgKind::Lifetime(_) | GenericArgKind::Const(_) => false,
    })
}

/// Walks into `ty` and returns `true` if any inner type is an instance of the given type, or adt
/// constructor of the same type.
///
/// This method also recurses into opaque type predicates, so call it with `impl Trait<U>` and `U`
/// will also return `true`.
pub fn contains_ty_adt_constructor_opaque<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>, needle: Ty<'tcx>) -> bool {
    fn contains_ty_adt_constructor_opaque_inner<'tcx>(
        cx: &LateContext<'tcx>,
        ty: Ty<'tcx>,
        needle: Ty<'tcx>,
        seen: &mut FxHashSet<DefId>,
    ) -> bool {
        ty.walk().any(|inner| match inner.unpack() {
            GenericArgKind::Type(inner_ty) => {
                if inner_ty == needle {
                    return true;
                }

                if inner_ty.ty_adt_def() == needle.ty_adt_def() {
                    return true;
                }

                if let ty::Alias(ty::Opaque, ty::AliasTy { def_id, .. }) = *inner_ty.kind() {
                    if !seen.insert(def_id) {
                        return false;
                    }

                    for (predicate, _span) in cx.tcx.explicit_item_bounds(def_id).instantiate_identity_iter_copied() {
                        match predicate.kind().skip_binder() {
                            // For `impl Trait<U>`, it will register a predicate of `T: Trait<U>`, so we go through
                            // and check substitutions to find `U`.
                            ty::ClauseKind::Trait(trait_predicate) => {
                                if trait_predicate
                                    .trait_ref
                                    .args
                                    .types()
                                    .skip(1) // Skip the implicit `Self` generic parameter
                                    .any(|ty| contains_ty_adt_constructor_opaque_inner(cx, ty, needle, seen))
                                {
                                    return true;
                                }
                            },
                            // For `impl Trait<Assoc=U>`, it will register a predicate of `<T as Trait>::Assoc = U`,
                            // so we check the term for `U`.
                            ty::ClauseKind::Projection(projection_predicate) => {
                                if let ty::TermKind::Ty(ty) = projection_predicate.term.unpack() {
                                    if contains_ty_adt_constructor_opaque_inner(cx, ty, needle, seen) {
                                        return true;
                                    }
                                };
                            },
                            _ => (),
                        }
                    }
                }

                false
            },
            GenericArgKind::Lifetime(_) | GenericArgKind::Const(_) => false,
        })
    }

    // A hash set to ensure that the same opaque type (`impl Trait` in RPIT or TAIT) is not
    // visited twice.
    let mut seen = FxHashSet::default();
    contains_ty_adt_constructor_opaque_inner(cx, ty, needle, &mut seen)
}

/// Resolves `<T as Iterator>::Item` for `T`
/// Do not invoke without first verifying that the type implements `Iterator`
pub fn get_iterator_item_ty<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> Option<Ty<'tcx>> {
    cx.tcx
        .get_diagnostic_item(sym::Iterator)
        .and_then(|iter_did| cx.get_associated_type(ty, iter_did, "Item"))
}

/// Get the diagnostic name of a type, e.g. `sym::HashMap`. To check if a type
/// implements a trait marked with a diagnostic item use [`implements_trait`].
///
/// For a further exploitation what diagnostic items are see [diagnostic items] in
/// rustc-dev-guide.
///
/// [Diagnostic Items]: https://rustc-dev-guide.rust-lang.org/diagnostics/diagnostic-items.html
pub fn get_type_diagnostic_name(cx: &LateContext<'_>, ty: Ty<'_>) -> Option<Symbol> {
    match ty.kind() {
        ty::Adt(adt, _) => cx.tcx.get_diagnostic_name(adt.did()),
        _ => None,
    }
}

/// Returns true if ty has `iter` or `iter_mut` methods
pub fn has_iter_method(cx: &LateContext<'_>, probably_ref_ty: Ty<'_>) -> Option<Symbol> {
    // FIXME: instead of this hard-coded list, we should check if `<adt>::iter`
    // exists and has the desired signature. Unfortunately FnCtxt is not exported
    // so we can't use its `lookup_method` method.
    let into_iter_collections: &[Symbol] = &[
        sym::Vec,
        sym::Option,
        sym::Result,
        sym::BTreeMap,
        sym::BTreeSet,
        sym::VecDeque,
        sym::LinkedList,
        sym::BinaryHeap,
        sym::HashSet,
        sym::HashMap,
        sym::PathBuf,
        sym::Path,
        sym::Receiver,
    ];

    let ty_to_check = match probably_ref_ty.kind() {
        ty::Ref(_, ty_to_check, _) => *ty_to_check,
        _ => probably_ref_ty,
    };

    let def_id = match ty_to_check.kind() {
        ty::Array(..) => return Some(sym::array),
        ty::Slice(..) => return Some(sym::slice),
        ty::Adt(adt, _) => adt.did(),
        _ => return None,
    };

    for &name in into_iter_collections {
        if cx.tcx.is_diagnostic_item(name, def_id) {
            return Some(cx.tcx.item_name(def_id));
        }
    }
    None
}

/// Checks whether a type implements a trait.
/// The function returns false in case the type contains an inference variable.
///
/// See:
/// * [`get_trait_def_id`](super::get_trait_def_id) to get a trait [`DefId`].
/// * [Common tools for writing lints] for an example how to use this function and other options.
///
/// [Common tools for writing lints]: https://github.com/rust-lang/rust-clippy/blob/master/book/src/development/common_tools_writing_lints.md#checking-if-a-type-implements-a-specific-trait
pub fn implements_trait<'tcx>(
    cx: &LateContext<'tcx>,
    ty: Ty<'tcx>,
    trait_id: DefId,
    args: &[GenericArg<'tcx>],
) -> bool {
    implements_trait_with_env_from_iter(cx.tcx, cx.param_env, ty, trait_id, None, args.iter().map(|&x| Some(x)))
}

/// Same as `implements_trait` but allows using a `ParamEnv` different from the lint context.
///
/// The `callee_id` argument is used to determine whether this is a function call in a `const fn`
/// environment, used for checking const traits.
pub fn implements_trait_with_env<'tcx>(
    tcx: TyCtxt<'tcx>,
    param_env: ParamEnv<'tcx>,
    ty: Ty<'tcx>,
    trait_id: DefId,
    callee_id: Option<DefId>,
    args: &[GenericArg<'tcx>],
) -> bool {
    implements_trait_with_env_from_iter(tcx, param_env, ty, trait_id, callee_id, args.iter().map(|&x| Some(x)))
}

/// Same as `implements_trait_from_env` but takes the arguments as an iterator.
pub fn implements_trait_with_env_from_iter<'tcx>(
    tcx: TyCtxt<'tcx>,
    param_env: ParamEnv<'tcx>,
    ty: Ty<'tcx>,
    trait_id: DefId,
    callee_id: Option<DefId>,
    args: impl IntoIterator<Item = impl Into<Option<GenericArg<'tcx>>>>,
) -> bool {
    // Clippy shouldn't have infer types
    assert!(!ty.has_infer());

    // If a `callee_id` is passed, then we assert that it is a body owner
    // through calling `body_owner_kind`, which would panic if the callee
    // does not have a body.
    if let Some(callee_id) = callee_id {
        let _ = tcx.hir().body_owner_kind(callee_id);
    }

    let ty = tcx.erase_regions(ty);
    if ty.has_escaping_bound_vars() {
        return false;
    }

    let infcx = tcx.infer_ctxt().build();
    let args = args
        .into_iter()
        .map(|arg| {
            arg.into().unwrap_or_else(|| {
                let orig = TypeVariableOrigin {
                    kind: TypeVariableOriginKind::MiscVariable,
                    span: DUMMY_SP,
                };
                infcx.next_ty_var(orig).into()
            })
        })
        .collect::<Vec<_>>();

    // If an effect arg was not specified, we need to specify it.
    let effect_arg = if tcx
        .generics_of(trait_id)
        .host_effect_index
        .is_some_and(|x| args.get(x - 1).is_none())
    {
        Some(GenericArg::from(callee_id.map_or(tcx.consts.true_, |def_id| {
            tcx.expected_host_effect_param_for_body(def_id)
        })))
    } else {
        None
    };

    let trait_ref = TraitRef::new(
        tcx,
        trait_id,
        Some(GenericArg::from(ty)).into_iter().chain(args).chain(effect_arg),
    );

    debug_assert_matches!(
        tcx.def_kind(trait_id),
        DefKind::Trait | DefKind::TraitAlias,
        "`DefId` must belong to a trait or trait alias"
    );
    #[cfg(debug_assertions)]
    assert_generic_args_match(tcx, trait_id, trait_ref.args);

    let obligation = Obligation {
        cause: ObligationCause::dummy(),
        param_env,
        recursion_depth: 0,
        predicate: ty::Binder::dummy(trait_ref).to_predicate(tcx),
    };
    infcx
        .evaluate_obligation(&obligation)
        .is_ok_and(EvaluationResult::must_apply_modulo_regions)
}

/// Checks whether this type implements `Drop`.
pub fn has_drop<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
    match ty.ty_adt_def() {
        Some(def) => def.has_dtor(cx.tcx),
        None => false,
    }
}

// Returns whether the type has #[must_use] attribute
pub fn is_must_use_ty<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
    match ty.kind() {
        ty::Adt(adt, _) => cx.tcx.has_attr(adt.did(), sym::must_use),
        ty::Foreign(did) => cx.tcx.has_attr(*did, sym::must_use),
        ty::Slice(ty) | ty::Array(ty, _) | ty::RawPtr(ty::TypeAndMut { ty, .. }) | ty::Ref(_, ty, _) => {
            // for the Array case we don't need to care for the len == 0 case
            // because we don't want to lint functions returning empty arrays
            is_must_use_ty(cx, *ty)
        },
        ty::Tuple(args) => args.iter().any(|ty| is_must_use_ty(cx, ty)),
        ty::Alias(ty::Opaque, ty::AliasTy { def_id, .. }) => {
            for (predicate, _) in cx.tcx.explicit_item_bounds(def_id).skip_binder() {
                if let ty::ClauseKind::Trait(trait_predicate) = predicate.kind().skip_binder() {
                    if cx.tcx.has_attr(trait_predicate.trait_ref.def_id, sym::must_use) {
                        return true;
                    }
                }
            }
            false
        },
        ty::Dynamic(binder, _, _) => {
            for predicate in *binder {
                if let ty::ExistentialPredicate::Trait(ref trait_ref) = predicate.skip_binder() {
                    if cx.tcx.has_attr(trait_ref.def_id, sym::must_use) {
                        return true;
                    }
                }
            }
            false
        },
        _ => false,
    }
}

// FIXME: Per https://doc.rust-lang.org/nightly/nightly-rustc/rustc_trait_selection/infer/at/struct.At.html#method.normalize
// this function can be removed once the `normalize` method does not panic when normalization does
// not succeed
/// Checks if `Ty` is normalizable. This function is useful
/// to avoid crashes on `layout_of`.
pub fn is_normalizable<'tcx>(cx: &LateContext<'tcx>, param_env: ty::ParamEnv<'tcx>, ty: Ty<'tcx>) -> bool {
    is_normalizable_helper(cx, param_env, ty, &mut FxHashMap::default())
}

fn is_normalizable_helper<'tcx>(
    cx: &LateContext<'tcx>,
    param_env: ty::ParamEnv<'tcx>,
    ty: Ty<'tcx>,
    cache: &mut FxHashMap<Ty<'tcx>, bool>,
) -> bool {
    if let Some(&cached_result) = cache.get(&ty) {
        return cached_result;
    }
    // prevent recursive loops, false-negative is better than endless loop leading to stack overflow
    cache.insert(ty, false);
    let infcx = cx.tcx.infer_ctxt().build();
    let cause = rustc_middle::traits::ObligationCause::dummy();
    let result = if infcx.at(&cause, param_env).query_normalize(ty).is_ok() {
        match ty.kind() {
            ty::Adt(def, args) => def.variants().iter().all(|variant| {
                variant
                    .fields
                    .iter()
                    .all(|field| is_normalizable_helper(cx, param_env, field.ty(cx.tcx, args), cache))
            }),
            _ => ty.walk().all(|generic_arg| match generic_arg.unpack() {
                GenericArgKind::Type(inner_ty) if inner_ty != ty => {
                    is_normalizable_helper(cx, param_env, inner_ty, cache)
                },
                _ => true, // if inner_ty == ty, we've already checked it
            }),
        }
    } else {
        false
    };
    cache.insert(ty, result);
    result
}

/// Returns `true` if the given type is a non aggregate primitive (a `bool` or `char`, any
/// integer or floating-point number type). For checking aggregation of primitive types (e.g.
/// tuples and slices of primitive type) see `is_recursively_primitive_type`
pub fn is_non_aggregate_primitive_type(ty: Ty<'_>) -> bool {
    matches!(ty.kind(), ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) | ty::Float(_))
}

/// Returns `true` if the given type is a primitive (a `bool` or `char`, any integer or
/// floating-point number type, a `str`, or an array, slice, or tuple of those types).
pub fn is_recursively_primitive_type(ty: Ty<'_>) -> bool {
    match *ty.kind() {
        ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) | ty::Float(_) | ty::Str => true,
        ty::Ref(_, inner, _) if inner.is_str() => true,
        ty::Array(inner_type, _) | ty::Slice(inner_type) => is_recursively_primitive_type(inner_type),
        ty::Tuple(inner_types) => inner_types.iter().all(is_recursively_primitive_type),
        _ => false,
    }
}

/// Checks if the type is a reference equals to a diagnostic item
pub fn is_type_ref_to_diagnostic_item(cx: &LateContext<'_>, ty: Ty<'_>, diag_item: Symbol) -> bool {
    match ty.kind() {
        ty::Ref(_, ref_ty, _) => match ref_ty.kind() {
            ty::Adt(adt, _) => cx.tcx.is_diagnostic_item(diag_item, adt.did()),
            _ => false,
        },
        _ => false,
    }
}

/// Checks if the type is equal to a diagnostic item. To check if a type implements a
/// trait marked with a diagnostic item use [`implements_trait`].
///
/// For a further exploitation what diagnostic items are see [diagnostic items] in
/// rustc-dev-guide.
///
/// ---
///
/// If you change the signature, remember to update the internal lint `MatchTypeOnDiagItem`
///
/// [Diagnostic Items]: https://rustc-dev-guide.rust-lang.org/diagnostics/diagnostic-items.html
pub fn is_type_diagnostic_item(cx: &LateContext<'_>, ty: Ty<'_>, diag_item: Symbol) -> bool {
    match ty.kind() {
        ty::Adt(adt, _) => cx.tcx.is_diagnostic_item(diag_item, adt.did()),
        _ => false,
    }
}

/// Checks if the type is equal to a lang item.
///
/// Returns `false` if the `LangItem` is not defined.
pub fn is_type_lang_item(cx: &LateContext<'_>, ty: Ty<'_>, lang_item: hir::LangItem) -> bool {
    match ty.kind() {
        ty::Adt(adt, _) => cx.tcx.lang_items().get(lang_item) == Some(adt.did()),
        _ => false,
    }
}

/// Gets the diagnostic name of the type, if it has one
pub fn type_diagnostic_name(cx: &LateContext<'_>, ty: Ty<'_>) -> Option<Symbol> {
    ty.ty_adt_def().and_then(|adt| cx.tcx.get_diagnostic_name(adt.did()))
}

/// Return `true` if the passed `typ` is `isize` or `usize`.
pub fn is_isize_or_usize(typ: Ty<'_>) -> bool {
    matches!(typ.kind(), ty::Int(IntTy::Isize) | ty::Uint(UintTy::Usize))
}

/// Checks if type is struct, enum or union type with the given def path.
///
/// If the type is a diagnostic item, use `is_type_diagnostic_item` instead.
/// If you change the signature, remember to update the internal lint `MatchTypeOnDiagItem`
pub fn match_type(cx: &LateContext<'_>, ty: Ty<'_>, path: &[&str]) -> bool {
    match ty.kind() {
        ty::Adt(adt, _) => match_def_path(cx, adt.did(), path),
        _ => false,
    }
}

/// Checks if the drop order for a type matters. Some std types implement drop solely to
/// deallocate memory. For these types, and composites containing them, changing the drop order
/// won't result in any observable side effects.
pub fn needs_ordered_drop<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
    fn needs_ordered_drop_inner<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>, seen: &mut FxHashSet<Ty<'tcx>>) -> bool {
        if !seen.insert(ty) {
            return false;
        }
        if !ty.has_significant_drop(cx.tcx, cx.param_env) {
            false
        }
        // Check for std types which implement drop, but only for memory allocation.
        else if is_type_lang_item(cx, ty, LangItem::OwnedBox)
            || matches!(
                get_type_diagnostic_name(cx, ty),
                Some(sym::HashSet | sym::Rc | sym::Arc | sym::cstring_type | sym::RcWeak | sym::ArcWeak)
            )
        {
            // Check all of the generic arguments.
            if let ty::Adt(_, subs) = ty.kind() {
                subs.types().any(|ty| needs_ordered_drop_inner(cx, ty, seen))
            } else {
                true
            }
        } else if !cx
            .tcx
            .lang_items()
            .drop_trait()
            .map_or(false, |id| implements_trait(cx, ty, id, &[]))
        {
            // This type doesn't implement drop, so no side effects here.
            // Check if any component type has any.
            match ty.kind() {
                ty::Tuple(fields) => fields.iter().any(|ty| needs_ordered_drop_inner(cx, ty, seen)),
                ty::Array(ty, _) => needs_ordered_drop_inner(cx, *ty, seen),
                ty::Adt(adt, subs) => adt
                    .all_fields()
                    .map(|f| f.ty(cx.tcx, subs))
                    .any(|ty| needs_ordered_drop_inner(cx, ty, seen)),
                _ => true,
            }
        } else {
            true
        }
    }

    needs_ordered_drop_inner(cx, ty, &mut FxHashSet::default())
}

/// Peels off all references on the type. Returns the underlying type and the number of references
/// removed.
pub fn peel_mid_ty_refs(ty: Ty<'_>) -> (Ty<'_>, usize) {
    fn peel(ty: Ty<'_>, count: usize) -> (Ty<'_>, usize) {
        if let ty::Ref(_, ty, _) = ty.kind() {
            peel(*ty, count + 1)
        } else {
            (ty, count)
        }
    }
    peel(ty, 0)
}

/// Peels off all references on the type. Returns the underlying type, the number of references
/// removed, and whether the pointer is ultimately mutable or not.
pub fn peel_mid_ty_refs_is_mutable(ty: Ty<'_>) -> (Ty<'_>, usize, Mutability) {
    fn f(ty: Ty<'_>, count: usize, mutability: Mutability) -> (Ty<'_>, usize, Mutability) {
        match ty.kind() {
            ty::Ref(_, ty, Mutability::Mut) => f(*ty, count + 1, mutability),
            ty::Ref(_, ty, Mutability::Not) => f(*ty, count + 1, Mutability::Not),
            _ => (ty, count, mutability),
        }
    }
    f(ty, 0, Mutability::Mut)
}

/// Returns `true` if the given type is an `unsafe` function.
pub fn type_is_unsafe_function<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
    match ty.kind() {
        ty::FnDef(..) | ty::FnPtr(_) => ty.fn_sig(cx.tcx).unsafety() == Unsafety::Unsafe,
        _ => false,
    }
}

/// Returns the base type for HIR references and pointers.
pub fn walk_ptrs_hir_ty<'tcx>(ty: &'tcx hir::Ty<'tcx>) -> &'tcx hir::Ty<'tcx> {
    match ty.kind {
        TyKind::Ptr(ref mut_ty) | TyKind::Ref(_, ref mut_ty) => walk_ptrs_hir_ty(mut_ty.ty),
        _ => ty,
    }
}

/// Returns the base type for references and raw pointers, and count reference
/// depth.
pub fn walk_ptrs_ty_depth(ty: Ty<'_>) -> (Ty<'_>, usize) {
    fn inner(ty: Ty<'_>, depth: usize) -> (Ty<'_>, usize) {
        match ty.kind() {
            ty::Ref(_, ty, _) => inner(*ty, depth + 1),
            _ => (ty, depth),
        }
    }
    inner(ty, 0)
}

/// Returns `true` if types `a` and `b` are same types having same `Const` generic args,
/// otherwise returns `false`
pub fn same_type_and_consts<'tcx>(a: Ty<'tcx>, b: Ty<'tcx>) -> bool {
    match (&a.kind(), &b.kind()) {
        (&ty::Adt(did_a, args_a), &ty::Adt(did_b, args_b)) => {
            if did_a != did_b {
                return false;
            }

            args_a
                .iter()
                .zip(args_b.iter())
                .all(|(arg_a, arg_b)| match (arg_a.unpack(), arg_b.unpack()) {
                    (GenericArgKind::Const(inner_a), GenericArgKind::Const(inner_b)) => inner_a == inner_b,
                    (GenericArgKind::Type(type_a), GenericArgKind::Type(type_b)) => {
                        same_type_and_consts(type_a, type_b)
                    },
                    _ => true,
                })
        },
        _ => a == b,
    }
}

/// Checks if a given type looks safe to be uninitialized.
pub fn is_uninit_value_valid_for_ty<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
    cx.tcx
        .check_validity_requirement((ValidityRequirement::Uninit, cx.param_env.and(ty)))
        .unwrap_or_else(|_| is_uninit_value_valid_for_ty_fallback(cx, ty))
}

/// A fallback for polymorphic types, which are not supported by `check_validity_requirement`.
fn is_uninit_value_valid_for_ty_fallback<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
    match *ty.kind() {
        // The array length may be polymorphic, let's try the inner type.
        ty::Array(component, _) => is_uninit_value_valid_for_ty(cx, component),
        // Peek through tuples and try their fallbacks.
        ty::Tuple(types) => types.iter().all(|ty| is_uninit_value_valid_for_ty(cx, ty)),
        // Unions are always fine right now.
        // This includes MaybeUninit, the main way people use uninitialized memory.
        // For ADTs, we could look at all fields just like for tuples, but that's potentially
        // exponential, so let's avoid doing that for now. Code doing that is sketchy enough to
        // just use an `#[allow()]`.
        ty::Adt(adt, _) => adt.is_union(),
        // For the rest, conservatively assume that they cannot be uninit.
        _ => false,
    }
}

/// Gets an iterator over all predicates which apply to the given item.
pub fn all_predicates_of(tcx: TyCtxt<'_>, id: DefId) -> impl Iterator<Item = &(ty::Clause<'_>, Span)> {
    let mut next_id = Some(id);
    iter::from_fn(move || {
        next_id.take().map(|id| {
            let preds = tcx.predicates_of(id);
            next_id = preds.parent;
            preds.predicates.iter()
        })
    })
    .flatten()
}

/// A signature for a function like type.
#[derive(Clone, Copy)]
pub enum ExprFnSig<'tcx> {
    Sig(Binder<'tcx, FnSig<'tcx>>, Option<DefId>),
    Closure(Option<&'tcx FnDecl<'tcx>>, Binder<'tcx, FnSig<'tcx>>),
    Trait(Binder<'tcx, Ty<'tcx>>, Option<Binder<'tcx, Ty<'tcx>>>, Option<DefId>),
}
impl<'tcx> ExprFnSig<'tcx> {
    /// Gets the argument type at the given offset. This will return `None` when the index is out of
    /// bounds only for variadic functions, otherwise this will panic.
    pub fn input(self, i: usize) -> Option<Binder<'tcx, Ty<'tcx>>> {
        match self {
            Self::Sig(sig, _) => {
                if sig.c_variadic() {
                    sig.inputs().map_bound(|inputs| inputs.get(i).copied()).transpose()
                } else {
                    Some(sig.input(i))
                }
            },
            Self::Closure(_, sig) => Some(sig.input(0).map_bound(|ty| ty.tuple_fields()[i])),
            Self::Trait(inputs, _, _) => Some(inputs.map_bound(|ty| ty.tuple_fields()[i])),
        }
    }

    /// Gets the argument type at the given offset. For closures this will also get the type as
    /// written. This will return `None` when the index is out of bounds only for variadic
    /// functions, otherwise this will panic.
    pub fn input_with_hir(self, i: usize) -> Option<(Option<&'tcx hir::Ty<'tcx>>, Binder<'tcx, Ty<'tcx>>)> {
        match self {
            Self::Sig(sig, _) => {
                if sig.c_variadic() {
                    sig.inputs()
                        .map_bound(|inputs| inputs.get(i).copied())
                        .transpose()
                        .map(|arg| (None, arg))
                } else {
                    Some((None, sig.input(i)))
                }
            },
            Self::Closure(decl, sig) => Some((
                decl.and_then(|decl| decl.inputs.get(i)),
                sig.input(0).map_bound(|ty| ty.tuple_fields()[i]),
            )),
            Self::Trait(inputs, _, _) => Some((None, inputs.map_bound(|ty| ty.tuple_fields()[i]))),
        }
    }

    /// Gets the result type, if one could be found. Note that the result type of a trait may not be
    /// specified.
    pub fn output(self) -> Option<Binder<'tcx, Ty<'tcx>>> {
        match self {
            Self::Sig(sig, _) | Self::Closure(_, sig) => Some(sig.output()),
            Self::Trait(_, output, _) => output,
        }
    }

    pub fn predicates_id(&self) -> Option<DefId> {
        if let ExprFnSig::Sig(_, id) | ExprFnSig::Trait(_, _, id) = *self {
            id
        } else {
            None
        }
    }
}

/// If the expression is function like, get the signature for it.
pub fn expr_sig<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'_>) -> Option<ExprFnSig<'tcx>> {
    if let Res::Def(DefKind::Fn | DefKind::Ctor(_, CtorKind::Fn) | DefKind::AssocFn, id) = path_res(cx, expr) {
        Some(ExprFnSig::Sig(cx.tcx.fn_sig(id).instantiate_identity(), Some(id)))
    } else {
        ty_sig(cx, cx.typeck_results().expr_ty_adjusted(expr).peel_refs())
    }
}

/// If the type is function like, get the signature for it.
pub fn ty_sig<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> Option<ExprFnSig<'tcx>> {
    if ty.is_box() {
        return ty_sig(cx, ty.boxed_ty());
    }
    match *ty.kind() {
        ty::Closure(id, subs) => {
            let decl = id
                .as_local()
                .and_then(|id| cx.tcx.hir().fn_decl_by_hir_id(cx.tcx.local_def_id_to_hir_id(id)));
            Some(ExprFnSig::Closure(decl, subs.as_closure().sig()))
        },
        ty::FnDef(id, subs) => Some(ExprFnSig::Sig(cx.tcx.fn_sig(id).instantiate(cx.tcx, subs), Some(id))),
        ty::Alias(ty::Opaque, ty::AliasTy { def_id, args, .. }) => sig_from_bounds(
            cx,
            ty,
            cx.tcx.item_bounds(def_id).iter_instantiated(cx.tcx, args),
            cx.tcx.opt_parent(def_id),
        ),
        ty::FnPtr(sig) => Some(ExprFnSig::Sig(sig, None)),
        ty::Dynamic(bounds, _, _) => {
            let lang_items = cx.tcx.lang_items();
            match bounds.principal() {
                Some(bound)
                    if Some(bound.def_id()) == lang_items.fn_trait()
                        || Some(bound.def_id()) == lang_items.fn_once_trait()
                        || Some(bound.def_id()) == lang_items.fn_mut_trait() =>
                {
                    let output = bounds
                        .projection_bounds()
                        .find(|p| lang_items.fn_once_output().map_or(false, |id| id == p.item_def_id()))
                        .map(|p| p.map_bound(|p| p.term.ty().unwrap()));
                    Some(ExprFnSig::Trait(bound.map_bound(|b| b.args.type_at(0)), output, None))
                },
                _ => None,
            }
        },
        ty::Alias(ty::Projection, proj) => match cx.tcx.try_normalize_erasing_regions(cx.param_env, ty) {
            Ok(normalized_ty) if normalized_ty != ty => ty_sig(cx, normalized_ty),
            _ => sig_for_projection(cx, proj).or_else(|| sig_from_bounds(cx, ty, cx.param_env.caller_bounds(), None)),
        },
        ty::Param(_) => sig_from_bounds(cx, ty, cx.param_env.caller_bounds(), None),
        _ => None,
    }
}

fn sig_from_bounds<'tcx>(
    cx: &LateContext<'tcx>,
    ty: Ty<'tcx>,
    predicates: impl IntoIterator<Item = ty::Clause<'tcx>>,
    predicates_id: Option<DefId>,
) -> Option<ExprFnSig<'tcx>> {
    let mut inputs = None;
    let mut output = None;
    let lang_items = cx.tcx.lang_items();

    for pred in predicates {
        match pred.kind().skip_binder() {
            ty::ClauseKind::Trait(p)
                if (lang_items.fn_trait() == Some(p.def_id())
                    || lang_items.fn_mut_trait() == Some(p.def_id())
                    || lang_items.fn_once_trait() == Some(p.def_id()))
                    && p.self_ty() == ty =>
            {
                let i = pred.kind().rebind(p.trait_ref.args.type_at(1));
                if inputs.map_or(false, |inputs| i != inputs) {
                    // Multiple different fn trait impls. Is this even allowed?
                    return None;
                }
                inputs = Some(i);
            },
            ty::ClauseKind::Projection(p)
                if Some(p.projection_ty.def_id) == lang_items.fn_once_output() && p.projection_ty.self_ty() == ty =>
            {
                if output.is_some() {
                    // Multiple different fn trait impls. Is this even allowed?
                    return None;
                }
                output = Some(pred.kind().rebind(p.term.ty().unwrap()));
            },
            _ => (),
        }
    }

    inputs.map(|ty| ExprFnSig::Trait(ty, output, predicates_id))
}

fn sig_for_projection<'tcx>(cx: &LateContext<'tcx>, ty: AliasTy<'tcx>) -> Option<ExprFnSig<'tcx>> {
    let mut inputs = None;
    let mut output = None;
    let lang_items = cx.tcx.lang_items();

    for (pred, _) in cx
        .tcx
        .explicit_item_bounds(ty.def_id)
        .iter_instantiated_copied(cx.tcx, ty.args)
    {
        match pred.kind().skip_binder() {
            ty::ClauseKind::Trait(p)
                if (lang_items.fn_trait() == Some(p.def_id())
                    || lang_items.fn_mut_trait() == Some(p.def_id())
                    || lang_items.fn_once_trait() == Some(p.def_id())) =>
            {
                let i = pred.kind().rebind(p.trait_ref.args.type_at(1));

                if inputs.map_or(false, |inputs| inputs != i) {
                    // Multiple different fn trait impls. Is this even allowed?
                    return None;
                }
                inputs = Some(i);
            },
            ty::ClauseKind::Projection(p) if Some(p.projection_ty.def_id) == lang_items.fn_once_output() => {
                if output.is_some() {
                    // Multiple different fn trait impls. Is this even allowed?
                    return None;
                }
                output = pred.kind().rebind(p.term.ty()).transpose();
            },
            _ => (),
        }
    }

    inputs.map(|ty| ExprFnSig::Trait(ty, output, None))
}

#[derive(Clone, Copy)]
pub enum EnumValue {
    Unsigned(u128),
    Signed(i128),
}
impl core::ops::Add<u32> for EnumValue {
    type Output = Self;
    fn add(self, n: u32) -> Self::Output {
        match self {
            Self::Unsigned(x) => Self::Unsigned(x + u128::from(n)),
            Self::Signed(x) => Self::Signed(x + i128::from(n)),
        }
    }
}

/// Attempts to read the given constant as though it were an enum value.
#[expect(clippy::cast_possible_truncation, clippy::cast_possible_wrap)]
pub fn read_explicit_enum_value(tcx: TyCtxt<'_>, id: DefId) -> Option<EnumValue> {
    if let Ok(ConstValue::Scalar(Scalar::Int(value))) = tcx.const_eval_poly(id) {
        match tcx.type_of(id).instantiate_identity().kind() {
            ty::Int(_) => Some(EnumValue::Signed(match value.size().bytes() {
                1 => i128::from(value.assert_bits(Size::from_bytes(1)) as u8 as i8),
                2 => i128::from(value.assert_bits(Size::from_bytes(2)) as u16 as i16),
                4 => i128::from(value.assert_bits(Size::from_bytes(4)) as u32 as i32),
                8 => i128::from(value.assert_bits(Size::from_bytes(8)) as u64 as i64),
                16 => value.assert_bits(Size::from_bytes(16)) as i128,
                _ => return None,
            })),
            ty::Uint(_) => Some(EnumValue::Unsigned(match value.size().bytes() {
                1 => value.assert_bits(Size::from_bytes(1)),
                2 => value.assert_bits(Size::from_bytes(2)),
                4 => value.assert_bits(Size::from_bytes(4)),
                8 => value.assert_bits(Size::from_bytes(8)),
                16 => value.assert_bits(Size::from_bytes(16)),
                _ => return None,
            })),
            _ => None,
        }
    } else {
        None
    }
}

/// Gets the value of the given variant.
pub fn get_discriminant_value(tcx: TyCtxt<'_>, adt: AdtDef<'_>, i: VariantIdx) -> EnumValue {
    let variant = &adt.variant(i);
    match variant.discr {
        VariantDiscr::Explicit(id) => read_explicit_enum_value(tcx, id).unwrap(),
        VariantDiscr::Relative(x) => match adt.variant((i.as_usize() - x as usize).into()).discr {
            VariantDiscr::Explicit(id) => read_explicit_enum_value(tcx, id).unwrap() + x,
            VariantDiscr::Relative(_) => EnumValue::Unsigned(x.into()),
        },
    }
}

/// Check if the given type is either `core::ffi::c_void`, `std::os::raw::c_void`, or one of the
/// platform specific `libc::<platform>::c_void` types in libc.
pub fn is_c_void(cx: &LateContext<'_>, ty: Ty<'_>) -> bool {
    if let ty::Adt(adt, _) = ty.kind()
        && let &[krate, .., name] = &*cx.get_def_path(adt.did())
        && let sym::libc | sym::core | sym::std = krate
        && name == rustc_span::sym::c_void
    {
        true
    } else {
        false
    }
}

pub fn for_each_top_level_late_bound_region<B>(
    ty: Ty<'_>,
    f: impl FnMut(BoundRegion) -> ControlFlow<B>,
) -> ControlFlow<B> {
    struct V<F> {
        index: u32,
        f: F,
    }
    impl<'tcx, B, F: FnMut(BoundRegion) -> ControlFlow<B>> TypeVisitor<TyCtxt<'tcx>> for V<F> {
        type BreakTy = B;
        fn visit_region(&mut self, r: Region<'tcx>) -> ControlFlow<Self::BreakTy> {
            if let RegionKind::ReBound(idx, bound) = r.kind()
                && idx.as_u32() == self.index
            {
                (self.f)(bound)
            } else {
                ControlFlow::Continue(())
            }
        }
        fn visit_binder<T: TypeVisitable<TyCtxt<'tcx>>>(&mut self, t: &Binder<'tcx, T>) -> ControlFlow<Self::BreakTy> {
            self.index += 1;
            let res = t.super_visit_with(self);
            self.index -= 1;
            res
        }
    }
    ty.visit_with(&mut V { index: 0, f })
}

pub struct AdtVariantInfo {
    pub ind: usize,
    pub size: u64,

    /// (ind, size)
    pub fields_size: Vec<(usize, u64)>,
}

impl AdtVariantInfo {
    /// Returns ADT variants ordered by size
    pub fn new<'tcx>(cx: &LateContext<'tcx>, adt: AdtDef<'tcx>, subst: &'tcx List<GenericArg<'tcx>>) -> Vec<Self> {
        let mut variants_size = adt
            .variants()
            .iter()
            .enumerate()
            .map(|(i, variant)| {
                let mut fields_size = variant
                    .fields
                    .iter()
                    .enumerate()
                    .map(|(i, f)| (i, approx_ty_size(cx, f.ty(cx.tcx, subst))))
                    .collect::<Vec<_>>();
                fields_size.sort_by(|(_, a_size), (_, b_size)| (a_size.cmp(b_size)));

                Self {
                    ind: i,
                    size: fields_size.iter().map(|(_, size)| size).sum(),
                    fields_size,
                }
            })
            .collect::<Vec<_>>();
        variants_size.sort_by(|a, b| (b.size.cmp(&a.size)));
        variants_size
    }
}

/// Gets the struct or enum variant from the given `Res`
pub fn adt_and_variant_of_res<'tcx>(cx: &LateContext<'tcx>, res: Res) -> Option<(AdtDef<'tcx>, &'tcx VariantDef)> {
    match res {
        Res::Def(DefKind::Struct, id) => {
            let adt = cx.tcx.adt_def(id);
            Some((adt, adt.non_enum_variant()))
        },
        Res::Def(DefKind::Variant, id) => {
            let adt = cx.tcx.adt_def(cx.tcx.parent(id));
            Some((adt, adt.variant_with_id(id)))
        },
        Res::Def(DefKind::Ctor(CtorOf::Struct, _), id) => {
            let adt = cx.tcx.adt_def(cx.tcx.parent(id));
            Some((adt, adt.non_enum_variant()))
        },
        Res::Def(DefKind::Ctor(CtorOf::Variant, _), id) => {
            let var_id = cx.tcx.parent(id);
            let adt = cx.tcx.adt_def(cx.tcx.parent(var_id));
            Some((adt, adt.variant_with_id(var_id)))
        },
        Res::SelfCtor(id) => {
            let adt = cx.tcx.type_of(id).instantiate_identity().ty_adt_def().unwrap();
            Some((adt, adt.non_enum_variant()))
        },
        _ => None,
    }
}

/// Comes up with an "at least" guesstimate for the type's size, not taking into
/// account the layout of type parameters.
pub fn approx_ty_size<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> u64 {
    use rustc_middle::ty::layout::LayoutOf;
    if !is_normalizable(cx, cx.param_env, ty) {
        return 0;
    }
    match (cx.layout_of(ty).map(|layout| layout.size.bytes()), ty.kind()) {
        (Ok(size), _) => size,
        (Err(_), ty::Tuple(list)) => list.iter().map(|t| approx_ty_size(cx, t)).sum(),
        (Err(_), ty::Array(t, n)) => {
            n.try_eval_target_usize(cx.tcx, cx.param_env).unwrap_or_default() * approx_ty_size(cx, *t)
        },
        (Err(_), ty::Adt(def, subst)) if def.is_struct() => def
            .variants()
            .iter()
            .map(|v| {
                v.fields
                    .iter()
                    .map(|field| approx_ty_size(cx, field.ty(cx.tcx, subst)))
                    .sum::<u64>()
            })
            .sum(),
        (Err(_), ty::Adt(def, subst)) if def.is_enum() => def
            .variants()
            .iter()
            .map(|v| {
                v.fields
                    .iter()
                    .map(|field| approx_ty_size(cx, field.ty(cx.tcx, subst)))
                    .sum::<u64>()
            })
            .max()
            .unwrap_or_default(),
        (Err(_), ty::Adt(def, subst)) if def.is_union() => def
            .variants()
            .iter()
            .map(|v| {
                v.fields
                    .iter()
                    .map(|field| approx_ty_size(cx, field.ty(cx.tcx, subst)))
                    .max()
                    .unwrap_or_default()
            })
            .max()
            .unwrap_or_default(),
        (Err(_), _) => 0,
    }
}

/// Asserts that the given arguments match the generic parameters of the given item.
#[allow(dead_code)]
fn assert_generic_args_match<'tcx>(tcx: TyCtxt<'tcx>, did: DefId, args: &[GenericArg<'tcx>]) {
    let g = tcx.generics_of(did);
    let parent = g.parent.map(|did| tcx.generics_of(did));
    let count = g.parent_count + g.params.len();
    let params = parent
        .map_or([].as_slice(), |p| p.params.as_slice())
        .iter()
        .chain(&g.params)
        .map(|x| &x.kind);

    assert!(
        count == args.len(),
        "wrong number of arguments for `{did:?}`: expected `{count}`, found {}\n\
            note: the expected arguments are: `[{}]`\n\
            the given arguments are: `{args:#?}`",
        args.len(),
        params.clone().map(GenericParamDefKind::descr).format(", "),
    );

    if let Some((idx, (param, arg))) =
        params
            .clone()
            .zip(args.iter().map(|&x| x.unpack()))
            .enumerate()
            .find(|(_, (param, arg))| match (param, arg) {
                (GenericParamDefKind::Lifetime, GenericArgKind::Lifetime(_))
                | (GenericParamDefKind::Type { .. }, GenericArgKind::Type(_))
                | (GenericParamDefKind::Const { .. }, GenericArgKind::Const(_)) => false,
                (
                    GenericParamDefKind::Lifetime
                    | GenericParamDefKind::Type { .. }
                    | GenericParamDefKind::Const { .. },
                    _,
                ) => true,
            })
    {
        panic!(
            "incorrect argument for `{did:?}` at index `{idx}`: expected a {}, found `{arg:?}`\n\
                note: the expected arguments are `[{}]`\n\
                the given arguments are `{args:#?}`",
            param.descr(),
            params.clone().map(GenericParamDefKind::descr).format(", "),
        );
    }
}

/// Returns whether `ty` is never-like; i.e., `!` (never) or an enum with zero variants.
pub fn is_never_like(ty: Ty<'_>) -> bool {
    ty.is_never() || (ty.is_enum() && ty.ty_adt_def().is_some_and(|def| def.variants().is_empty()))
}

/// Makes the projection type for the named associated type in the given impl or trait impl.
///
/// This function is for associated types which are "known" to exist, and as such, will only return
/// `None` when debug assertions are disabled in order to prevent ICE's. With debug assertions
/// enabled this will check that the named associated type exists, the correct number of
/// arguments are given, and that the correct kinds of arguments are given (lifetime,
/// constant or type). This will not check if type normalization would succeed.
pub fn make_projection<'tcx>(
    tcx: TyCtxt<'tcx>,
    container_id: DefId,
    assoc_ty: Symbol,
    args: impl IntoIterator<Item = impl Into<GenericArg<'tcx>>>,
) -> Option<AliasTy<'tcx>> {
    fn helper<'tcx>(
        tcx: TyCtxt<'tcx>,
        container_id: DefId,
        assoc_ty: Symbol,
        args: GenericArgsRef<'tcx>,
    ) -> Option<AliasTy<'tcx>> {
        let Some(assoc_item) = tcx.associated_items(container_id).find_by_name_and_kind(
            tcx,
            Ident::with_dummy_span(assoc_ty),
            AssocKind::Type,
            container_id,
        ) else {
            debug_assert!(false, "type `{assoc_ty}` not found in `{container_id:?}`");
            return None;
        };
        #[cfg(debug_assertions)]
        assert_generic_args_match(tcx, assoc_item.def_id, args);

        Some(ty::AliasTy::new(tcx, assoc_item.def_id, args))
    }
    helper(
        tcx,
        container_id,
        assoc_ty,
        tcx.mk_args_from_iter(args.into_iter().map(Into::into)),
    )
}

/// Normalizes the named associated type in the given impl or trait impl.
///
/// This function is for associated types which are "known" to be valid with the given
/// arguments, and as such, will only return `None` when debug assertions are disabled in order
/// to prevent ICE's. With debug assertions enabled this will check that type normalization
/// succeeds as well as everything checked by `make_projection`.
pub fn make_normalized_projection<'tcx>(
    tcx: TyCtxt<'tcx>,
    param_env: ParamEnv<'tcx>,
    container_id: DefId,
    assoc_ty: Symbol,
    args: impl IntoIterator<Item = impl Into<GenericArg<'tcx>>>,
) -> Option<Ty<'tcx>> {
    fn helper<'tcx>(tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>, ty: AliasTy<'tcx>) -> Option<Ty<'tcx>> {
        #[cfg(debug_assertions)]
        if let Some((i, arg)) = ty
            .args
            .iter()
            .enumerate()
            .find(|(_, arg)| arg.has_escaping_bound_vars())
        {
            debug_assert!(
                false,
                "args contain late-bound region at index `{i}` which can't be normalized.\n\
                    use `TyCtxt::instantiate_bound_regions_with_erased`\n\
                    note: arg is `{arg:#?}`",
            );
            return None;
        }
        match tcx.try_normalize_erasing_regions(param_env, Ty::new_projection(tcx, ty.def_id, ty.args)) {
            Ok(ty) => Some(ty),
            Err(e) => {
                debug_assert!(false, "failed to normalize type `{ty}`: {e:#?}");
                None
            },
        }
    }
    helper(tcx, param_env, make_projection(tcx, container_id, assoc_ty, args)?)
}

/// Check if given type has inner mutability such as [`std::cell::Cell`] or [`std::cell::RefCell`]
/// etc.
pub fn is_interior_mut_ty<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
    match *ty.kind() {
        ty::Ref(_, inner_ty, mutbl) => mutbl == Mutability::Mut || is_interior_mut_ty(cx, inner_ty),
        ty::Slice(inner_ty) => is_interior_mut_ty(cx, inner_ty),
        ty::Array(inner_ty, size) => {
            size.try_eval_target_usize(cx.tcx, cx.param_env)
                .map_or(true, |u| u != 0)
                && is_interior_mut_ty(cx, inner_ty)
        },
        ty::Tuple(fields) => fields.iter().any(|ty| is_interior_mut_ty(cx, ty)),
        ty::Adt(def, args) => {
            // Special case for collections in `std` who's impl of `Hash` or `Ord` delegates to
            // that of their type parameters.  Note: we don't include `HashSet` and `HashMap`
            // because they have no impl for `Hash` or `Ord`.
            let def_id = def.did();
            let is_std_collection = [
                sym::Option,
                sym::Result,
                sym::LinkedList,
                sym::Vec,
                sym::VecDeque,
                sym::BTreeMap,
                sym::BTreeSet,
                sym::Rc,
                sym::Arc,
            ]
            .iter()
            .any(|diag_item| cx.tcx.is_diagnostic_item(*diag_item, def_id));
            let is_box = Some(def_id) == cx.tcx.lang_items().owned_box();
            if is_std_collection || is_box {
                // The type is mutable if any of its type parameters are
                args.types().any(|ty| is_interior_mut_ty(cx, ty))
            } else {
                !ty.has_escaping_bound_vars()
                    && cx.tcx.layout_of(cx.param_env.and(ty)).is_ok()
                    && !ty.is_freeze(cx.tcx, cx.param_env)
            }
        },
        _ => false,
    }
}

pub fn make_normalized_projection_with_regions<'tcx>(
    tcx: TyCtxt<'tcx>,
    param_env: ParamEnv<'tcx>,
    container_id: DefId,
    assoc_ty: Symbol,
    args: impl IntoIterator<Item = impl Into<GenericArg<'tcx>>>,
) -> Option<Ty<'tcx>> {
    fn helper<'tcx>(tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>, ty: AliasTy<'tcx>) -> Option<Ty<'tcx>> {
        #[cfg(debug_assertions)]
        if let Some((i, arg)) = ty
            .args
            .iter()
            .enumerate()
            .find(|(_, arg)| arg.has_escaping_bound_vars())
        {
            debug_assert!(
                false,
                "args contain late-bound region at index `{i}` which can't be normalized.\n\
                    use `TyCtxt::instantiate_bound_regions_with_erased`\n\
                    note: arg is `{arg:#?}`",
            );
            return None;
        }
        let cause = rustc_middle::traits::ObligationCause::dummy();
        match tcx
            .infer_ctxt()
            .build()
            .at(&cause, param_env)
            .query_normalize(Ty::new_projection(tcx, ty.def_id, ty.args))
        {
            Ok(ty) => Some(ty.value),
            Err(e) => {
                debug_assert!(false, "failed to normalize type `{ty}`: {e:#?}");
                None
            },
        }
    }
    helper(tcx, param_env, make_projection(tcx, container_id, assoc_ty, args)?)
}

pub fn normalize_with_regions<'tcx>(tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>, ty: Ty<'tcx>) -> Ty<'tcx> {
    let cause = rustc_middle::traits::ObligationCause::dummy();
    match tcx.infer_ctxt().build().at(&cause, param_env).query_normalize(ty) {
        Ok(ty) => ty.value,
        Err(_) => ty,
    }
}

/// Checks if the type is `core::mem::ManuallyDrop<_>`
pub fn is_manually_drop(ty: Ty<'_>) -> bool {
    ty.ty_adt_def().map_or(false, AdtDef::is_manually_drop)
}