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
//! Resolution of early vs late bound lifetimes.
//!
//! Name resolution for lifetimes is performed on the AST and embedded into HIR. From this
//! information, typechecking needs to transform the lifetime parameters into bound lifetimes.
//! Lifetimes can be early-bound or late-bound. Construction of typechecking terms needs to visit
//! the types in HIR to identify late-bound lifetimes and assign their Debruijn indices. This file
//! is also responsible for assigning their semantics to implicit lifetimes in trait objects.
use core::ops::ControlFlow;
use rustc_ast::visit::walk_list;
use rustc_data_structures::fx::{FxHashSet, FxIndexMap, FxIndexSet};
use rustc_hir as hir;
use rustc_hir::def::{DefKind, Res};
use rustc_hir::def_id::LocalDefId;
use rustc_hir::intravisit::{self, Visitor};
use rustc_hir::{GenericArg, GenericParam, GenericParamKind, HirId, HirIdMap, LifetimeName, Node};
use rustc_macros::extension;
use rustc_middle::bug;
use rustc_middle::hir::nested_filter;
use rustc_middle::middle::resolve_bound_vars::*;
use rustc_middle::query::Providers;
use rustc_middle::ty::{self, TyCtxt, TypeSuperVisitable, TypeVisitor};
use rustc_span::def_id::DefId;
use rustc_span::symbol::{sym, Ident};
use rustc_span::Span;
use std::fmt;
use crate::errors;
#[extension(trait RegionExt)]
impl ResolvedArg {
fn early(param: &GenericParam<'_>) -> (LocalDefId, ResolvedArg) {
debug!("ResolvedArg::early: def_id={:?}", param.def_id);
(param.def_id, ResolvedArg::EarlyBound(param.def_id.to_def_id()))
}
fn late(idx: u32, param: &GenericParam<'_>) -> (LocalDefId, ResolvedArg) {
let depth = ty::INNERMOST;
debug!(
"ResolvedArg::late: idx={:?}, param={:?} depth={:?} def_id={:?}",
idx, param, depth, param.def_id,
);
(param.def_id, ResolvedArg::LateBound(depth, idx, param.def_id.to_def_id()))
}
fn id(&self) -> Option<DefId> {
match *self {
ResolvedArg::StaticLifetime | ResolvedArg::Error(_) => None,
ResolvedArg::EarlyBound(id)
| ResolvedArg::LateBound(_, _, id)
| ResolvedArg::Free(_, id) => Some(id),
}
}
fn shifted(self, amount: u32) -> ResolvedArg {
match self {
ResolvedArg::LateBound(debruijn, idx, id) => {
ResolvedArg::LateBound(debruijn.shifted_in(amount), idx, id)
}
_ => self,
}
}
}
/// Maps the id of each bound variable reference to the variable decl
/// that it corresponds to.
///
/// FIXME. This struct gets converted to a `ResolveBoundVars` for
/// actual use. It has the same data, but indexed by `LocalDefId`. This
/// is silly.
#[derive(Debug, Default)]
struct NamedVarMap {
// maps from every use of a named (not anonymous) bound var to a
// `ResolvedArg` describing how that variable is bound
defs: HirIdMap<ResolvedArg>,
// Maps relevant hir items to the bound vars on them. These include:
// - function defs
// - function pointers
// - closures
// - trait refs
// - bound types (like `T` in `for<'a> T<'a>: Foo`)
late_bound_vars: HirIdMap<Vec<ty::BoundVariableKind>>,
}
struct BoundVarContext<'a, 'tcx> {
tcx: TyCtxt<'tcx>,
map: &'a mut NamedVarMap,
scope: ScopeRef<'a>,
}
#[derive(Debug)]
enum Scope<'a> {
/// Declares lifetimes, and each can be early-bound or late-bound.
/// The `DebruijnIndex` of late-bound lifetimes starts at `1` and
/// it should be shifted by the number of `Binder`s in between the
/// declaration `Binder` and the location it's referenced from.
Binder {
/// We use an IndexMap here because we want these lifetimes in order
/// for diagnostics.
bound_vars: FxIndexMap<LocalDefId, ResolvedArg>,
scope_type: BinderScopeType,
/// The late bound vars for a given item are stored by `HirId` to be
/// queried later. However, if we enter an elision scope, we have to
/// later append the elided bound vars to the list and need to know what
/// to append to.
hir_id: HirId,
s: ScopeRef<'a>,
/// If this binder comes from a where clause, specify how it was created.
/// This is used to diagnose inaccessible lifetimes in APIT:
/// ```ignore (illustrative)
/// fn foo(x: impl for<'a> Trait<'a, Assoc = impl Copy + 'a>) {}
/// ```
where_bound_origin: Option<hir::PredicateOrigin>,
},
/// Lifetimes introduced by a fn are scoped to the call-site for that fn,
/// if this is a fn body, otherwise the original definitions are used.
/// Unspecified lifetimes are inferred, unless an elision scope is nested,
/// e.g., `(&T, fn(&T) -> &T);` becomes `(&'_ T, for<'a> fn(&'a T) -> &'a T)`.
Body {
id: hir::BodyId,
s: ScopeRef<'a>,
},
/// Use a specific lifetime (if `Some`) or leave it unset (to be
/// inferred in a function body or potentially error outside one),
/// for the default choice of lifetime in a trait object type.
ObjectLifetimeDefault {
lifetime: Option<ResolvedArg>,
s: ScopeRef<'a>,
},
/// When we have nested trait refs, we concatenate late bound vars for inner
/// trait refs from outer ones. But we also need to include any HRTB
/// lifetimes encountered when identifying the trait that an associated type
/// is declared on.
Supertrait {
bound_vars: Vec<ty::BoundVariableKind>,
s: ScopeRef<'a>,
},
TraitRefBoundary {
s: ScopeRef<'a>,
},
/// Disallows capturing late-bound vars from parent scopes.
///
/// This is necessary for something like `for<T> [(); { /* references T */ }]:`,
/// since we don't do something more correct like replacing any captured
/// late-bound vars with early-bound params in the const's own generics.
LateBoundary {
s: ScopeRef<'a>,
what: &'static str,
},
Root {
opt_parent_item: Option<LocalDefId>,
},
}
#[derive(Copy, Clone, Debug)]
enum BinderScopeType {
/// Any non-concatenating binder scopes.
Normal,
/// Within a syntactic trait ref, there may be multiple poly trait refs that
/// are nested (under the `associated_type_bounds` feature). The binders of
/// the inner poly trait refs are extended from the outer poly trait refs
/// and don't increase the late bound depth. If you had
/// `T: for<'a> Foo<Bar: for<'b> Baz<'a, 'b>>`, then the `for<'b>` scope
/// would be `Concatenating`. This also used in trait refs in where clauses
/// where we have two binders `for<> T: for<> Foo` (I've intentionally left
/// out any lifetimes because they aren't needed to show the two scopes).
/// The inner `for<>` has a scope of `Concatenating`.
Concatenating,
}
// A helper struct for debugging scopes without printing parent scopes
struct TruncatedScopeDebug<'a>(&'a Scope<'a>);
impl<'a> fmt::Debug for TruncatedScopeDebug<'a> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
match self.0 {
Scope::Binder { bound_vars, scope_type, hir_id, where_bound_origin, s: _ } => f
.debug_struct("Binder")
.field("bound_vars", bound_vars)
.field("scope_type", scope_type)
.field("hir_id", hir_id)
.field("where_bound_origin", where_bound_origin)
.field("s", &"..")
.finish(),
Scope::Body { id, s: _ } => {
f.debug_struct("Body").field("id", id).field("s", &"..").finish()
}
Scope::ObjectLifetimeDefault { lifetime, s: _ } => f
.debug_struct("ObjectLifetimeDefault")
.field("lifetime", lifetime)
.field("s", &"..")
.finish(),
Scope::Supertrait { bound_vars, s: _ } => f
.debug_struct("Supertrait")
.field("bound_vars", bound_vars)
.field("s", &"..")
.finish(),
Scope::TraitRefBoundary { s: _ } => f.debug_struct("TraitRefBoundary").finish(),
Scope::LateBoundary { s: _, what } => {
f.debug_struct("LateBoundary").field("what", what).finish()
}
Scope::Root { opt_parent_item } => {
f.debug_struct("Root").field("opt_parent_item", &opt_parent_item).finish()
}
}
}
}
type ScopeRef<'a> = &'a Scope<'a>;
pub(crate) fn provide(providers: &mut Providers) {
*providers = Providers {
resolve_bound_vars,
named_variable_map: |tcx, id| tcx.resolve_bound_vars(id).defs.get(&id),
is_late_bound_map,
object_lifetime_default,
late_bound_vars_map: |tcx, id| tcx.resolve_bound_vars(id).late_bound_vars.get(&id),
..*providers
};
}
/// Computes the `ResolveBoundVars` map that contains data for an entire `Item`.
/// You should not read the result of this query directly, but rather use
/// `named_variable_map`, `is_late_bound_map`, etc.
#[instrument(level = "debug", skip(tcx))]
fn resolve_bound_vars(tcx: TyCtxt<'_>, local_def_id: hir::OwnerId) -> ResolveBoundVars {
let mut named_variable_map =
NamedVarMap { defs: Default::default(), late_bound_vars: Default::default() };
let mut visitor = BoundVarContext {
tcx,
map: &mut named_variable_map,
scope: &Scope::Root { opt_parent_item: None },
};
match tcx.hir_owner_node(local_def_id) {
hir::OwnerNode::Item(item) => visitor.visit_item(item),
hir::OwnerNode::ForeignItem(item) => visitor.visit_foreign_item(item),
hir::OwnerNode::TraitItem(item) => {
let scope =
Scope::Root { opt_parent_item: Some(tcx.local_parent(item.owner_id.def_id)) };
visitor.scope = &scope;
visitor.visit_trait_item(item)
}
hir::OwnerNode::ImplItem(item) => {
let scope =
Scope::Root { opt_parent_item: Some(tcx.local_parent(item.owner_id.def_id)) };
visitor.scope = &scope;
visitor.visit_impl_item(item)
}
hir::OwnerNode::Crate(_) => {}
hir::OwnerNode::Synthetic => unreachable!(),
}
let mut rl = ResolveBoundVars::default();
for (hir_id, v) in named_variable_map.defs {
let map = rl.defs.entry(hir_id.owner).or_default();
map.insert(hir_id.local_id, v);
}
for (hir_id, v) in named_variable_map.late_bound_vars {
let map = rl.late_bound_vars.entry(hir_id.owner).or_default();
map.insert(hir_id.local_id, v);
}
debug!(?rl.defs);
debug!(?rl.late_bound_vars);
rl
}
fn late_arg_as_bound_arg<'tcx>(
tcx: TyCtxt<'tcx>,
arg: &ResolvedArg,
param: &GenericParam<'tcx>,
) -> ty::BoundVariableKind {
match arg {
ResolvedArg::LateBound(_, _, def_id) => {
let name = tcx.hir().name(tcx.local_def_id_to_hir_id(def_id.expect_local()));
match param.kind {
GenericParamKind::Lifetime { .. } => {
ty::BoundVariableKind::Region(ty::BrNamed(*def_id, name))
}
GenericParamKind::Type { .. } => {
ty::BoundVariableKind::Ty(ty::BoundTyKind::Param(*def_id, name))
}
GenericParamKind::Const { .. } => ty::BoundVariableKind::Const,
}
}
_ => bug!("{:?} is not a late argument", arg),
}
}
impl<'a, 'tcx> BoundVarContext<'a, 'tcx> {
/// Returns the binders in scope and the type of `Binder` that should be created for a poly trait ref.
fn poly_trait_ref_binder_info(&mut self) -> (Vec<ty::BoundVariableKind>, BinderScopeType) {
let mut scope = self.scope;
let mut supertrait_bound_vars = vec![];
loop {
match scope {
Scope::Body { .. } | Scope::Root { .. } => {
break (vec![], BinderScopeType::Normal);
}
Scope::ObjectLifetimeDefault { s, .. } | Scope::LateBoundary { s, .. } => {
scope = s;
}
Scope::Supertrait { s, bound_vars } => {
supertrait_bound_vars = bound_vars.clone();
scope = s;
}
Scope::TraitRefBoundary { .. } => {
// We should only see super trait lifetimes if there is a `Binder` above
// though this may happen when we call `poly_trait_ref_binder_info` with
// an (erroneous, #113423) associated return type bound in an impl header.
if !supertrait_bound_vars.is_empty() {
self.tcx.dcx().delayed_bug(format!(
"found supertrait lifetimes without a binder to append \
them to: {supertrait_bound_vars:?}"
));
}
break (vec![], BinderScopeType::Normal);
}
Scope::Binder { hir_id, .. } => {
// Nested poly trait refs have the binders concatenated
let mut full_binders =
self.map.late_bound_vars.entry(*hir_id).or_default().clone();
full_binders.extend(supertrait_bound_vars);
break (full_binders, BinderScopeType::Concatenating);
}
}
}
}
fn visit_poly_trait_ref_inner(
&mut self,
trait_ref: &'tcx hir::PolyTraitRef<'tcx>,
non_lifetime_binder_allowed: NonLifetimeBinderAllowed,
) {
debug!("visit_poly_trait_ref(trait_ref={:?})", trait_ref);
let (mut binders, scope_type) = self.poly_trait_ref_binder_info();
let initial_bound_vars = binders.len() as u32;
let mut bound_vars: FxIndexMap<LocalDefId, ResolvedArg> = FxIndexMap::default();
let binders_iter =
trait_ref.bound_generic_params.iter().enumerate().map(|(late_bound_idx, param)| {
let pair = ResolvedArg::late(initial_bound_vars + late_bound_idx as u32, param);
let r = late_arg_as_bound_arg(self.tcx, &pair.1, param);
bound_vars.insert(pair.0, pair.1);
r
});
binders.extend(binders_iter);
if let NonLifetimeBinderAllowed::Deny(where_) = non_lifetime_binder_allowed {
deny_non_region_late_bound(self.tcx, &mut bound_vars, where_);
}
debug!(?binders);
self.record_late_bound_vars(trait_ref.trait_ref.hir_ref_id, binders);
// Always introduce a scope here, even if this is in a where clause and
// we introduced the binders around the bounded Ty. In that case, we
// just reuse the concatenation functionality also present in nested trait
// refs.
let scope = Scope::Binder {
hir_id: trait_ref.trait_ref.hir_ref_id,
bound_vars,
s: self.scope,
scope_type,
where_bound_origin: None,
};
self.with(scope, |this| {
walk_list!(this, visit_generic_param, trait_ref.bound_generic_params);
this.visit_trait_ref(&trait_ref.trait_ref);
});
}
}
enum NonLifetimeBinderAllowed {
Deny(&'static str),
Allow,
}
impl<'a, 'tcx> Visitor<'tcx> for BoundVarContext<'a, 'tcx> {
type NestedFilter = nested_filter::OnlyBodies;
fn nested_visit_map(&mut self) -> Self::Map {
self.tcx.hir()
}
fn visit_nested_body(&mut self, body: hir::BodyId) {
let body = self.tcx.hir().body(body);
self.with(Scope::Body { id: body.id(), s: self.scope }, |this| {
this.visit_body(body);
});
}
fn visit_expr(&mut self, e: &'tcx hir::Expr<'tcx>) {
if let hir::ExprKind::Closure(hir::Closure {
binder, bound_generic_params, fn_decl, ..
}) = e.kind
{
if let &hir::ClosureBinder::For { span: for_sp, .. } = binder {
fn span_of_infer(ty: &hir::Ty<'_>) -> Option<Span> {
/// Look for `_` anywhere in the signature of a `for<> ||` closure.
/// This is currently disallowed.
struct FindInferInClosureWithBinder;
impl<'v> Visitor<'v> for FindInferInClosureWithBinder {
type Result = ControlFlow<Span>;
fn visit_ty(&mut self, t: &'v hir::Ty<'v>) -> Self::Result {
if matches!(t.kind, hir::TyKind::Infer) {
ControlFlow::Break(t.span)
} else {
intravisit::walk_ty(self, t)
}
}
}
FindInferInClosureWithBinder.visit_ty(ty).break_value()
}
let infer_in_rt_sp = match fn_decl.output {
hir::FnRetTy::DefaultReturn(sp) => Some(sp),
hir::FnRetTy::Return(ty) => span_of_infer(ty),
};
let infer_spans = fn_decl
.inputs
.into_iter()
.filter_map(span_of_infer)
.chain(infer_in_rt_sp)
.collect::<Vec<_>>();
if !infer_spans.is_empty() {
self.tcx
.dcx()
.emit_err(errors::ClosureImplicitHrtb { spans: infer_spans, for_sp });
}
}
let (mut bound_vars, binders): (FxIndexMap<LocalDefId, ResolvedArg>, Vec<_>) =
bound_generic_params
.iter()
.enumerate()
.map(|(late_bound_idx, param)| {
let pair = ResolvedArg::late(late_bound_idx as u32, param);
let r = late_arg_as_bound_arg(self.tcx, &pair.1, param);
(pair, r)
})
.unzip();
deny_non_region_late_bound(self.tcx, &mut bound_vars, "closures");
self.record_late_bound_vars(e.hir_id, binders);
let scope = Scope::Binder {
hir_id: e.hir_id,
bound_vars,
s: self.scope,
scope_type: BinderScopeType::Normal,
where_bound_origin: None,
};
self.with(scope, |this| {
// a closure has no bounds, so everything
// contained within is scoped within its binder.
intravisit::walk_expr(this, e)
});
} else {
intravisit::walk_expr(self, e)
}
}
#[instrument(level = "debug", skip(self))]
fn visit_item(&mut self, item: &'tcx hir::Item<'tcx>) {
match &item.kind {
hir::ItemKind::Impl(hir::Impl { of_trait, .. }) => {
if let Some(of_trait) = of_trait {
self.record_late_bound_vars(of_trait.hir_ref_id, Vec::default());
}
}
_ => {}
}
match item.kind {
hir::ItemKind::Fn(_, generics, _) => {
self.visit_early_late(item.hir_id(), generics, |this| {
intravisit::walk_item(this, item);
});
}
hir::ItemKind::ExternCrate(_)
| hir::ItemKind::Use(..)
| hir::ItemKind::Macro(..)
| hir::ItemKind::Mod(..)
| hir::ItemKind::ForeignMod { .. }
| hir::ItemKind::Static(..)
| hir::ItemKind::GlobalAsm(..) => {
// These sorts of items have no lifetime parameters at all.
intravisit::walk_item(self, item);
}
hir::ItemKind::OpaqueTy(&hir::OpaqueTy {
origin:
hir::OpaqueTyOrigin::FnReturn(parent)
| hir::OpaqueTyOrigin::AsyncFn(parent)
| hir::OpaqueTyOrigin::TyAlias { parent, .. },
generics,
..
}) => {
// We want to start our early-bound indices at the end of the parent scope,
// not including any parent `impl Trait`s.
let mut bound_vars = FxIndexMap::default();
debug!(?generics.params);
for param in generics.params {
let (def_id, reg) = ResolvedArg::early(param);
bound_vars.insert(def_id, reg);
}
let scope = Scope::Root { opt_parent_item: Some(parent) };
self.with(scope, |this| {
let scope = Scope::Binder {
hir_id: item.hir_id(),
bound_vars,
s: this.scope,
scope_type: BinderScopeType::Normal,
where_bound_origin: None,
};
this.with(scope, |this| {
let scope = Scope::TraitRefBoundary { s: this.scope };
this.with(scope, |this| intravisit::walk_item(this, item))
});
})
}
hir::ItemKind::TyAlias(_, generics)
| hir::ItemKind::Const(_, generics, _)
| hir::ItemKind::Enum(_, generics)
| hir::ItemKind::Struct(_, generics)
| hir::ItemKind::Union(_, generics)
| hir::ItemKind::Trait(_, _, generics, ..)
| hir::ItemKind::TraitAlias(generics, ..)
| hir::ItemKind::Impl(&hir::Impl { generics, .. }) => {
// These kinds of items have only early-bound lifetime parameters.
self.visit_early(item.hir_id(), generics, |this| intravisit::walk_item(this, item));
}
}
}
fn visit_precise_capturing_arg(
&mut self,
arg: &'tcx hir::PreciseCapturingArg<'tcx>,
) -> Self::Result {
match *arg {
hir::PreciseCapturingArg::Lifetime(lt) => match lt.res {
LifetimeName::Param(def_id) => {
self.resolve_lifetime_ref(def_id, lt);
}
LifetimeName::Error => {}
LifetimeName::ImplicitObjectLifetimeDefault
| LifetimeName::Infer
| LifetimeName::Static => {
self.tcx.dcx().emit_err(errors::BadPreciseCapture {
span: lt.ident.span,
kind: "lifetime",
found: format!("`{}`", lt.ident.name),
});
}
},
hir::PreciseCapturingArg::Param(param) => match param.res {
Res::Def(DefKind::TyParam | DefKind::ConstParam, def_id)
| Res::SelfTyParam { trait_: def_id } => {
self.resolve_type_ref(def_id.expect_local(), param.hir_id);
}
Res::Err => {}
Res::SelfTyAlias { alias_to, .. } => {
self.tcx.dcx().emit_err(errors::PreciseCaptureSelfAlias {
span: param.ident.span,
self_span: self.tcx.def_span(alias_to),
what: self.tcx.def_descr(alias_to),
});
}
res => {
self.tcx.dcx().emit_err(errors::BadPreciseCapture {
span: param.ident.span,
kind: "type or const",
found: res.descr().to_string(),
});
}
},
}
}
fn visit_foreign_item(&mut self, item: &'tcx hir::ForeignItem<'tcx>) {
match item.kind {
hir::ForeignItemKind::Fn(_, _, generics) => {
self.visit_early_late(item.hir_id(), generics, |this| {
intravisit::walk_foreign_item(this, item);
})
}
hir::ForeignItemKind::Static(..) => {
intravisit::walk_foreign_item(self, item);
}
hir::ForeignItemKind::Type => {
intravisit::walk_foreign_item(self, item);
}
}
}
#[instrument(level = "debug", skip(self))]
fn visit_ty(&mut self, ty: &'tcx hir::Ty<'tcx>) {
match ty.kind {
hir::TyKind::BareFn(c) => {
let (mut bound_vars, binders): (FxIndexMap<LocalDefId, ResolvedArg>, Vec<_>) = c
.generic_params
.iter()
.enumerate()
.map(|(late_bound_idx, param)| {
let pair = ResolvedArg::late(late_bound_idx as u32, param);
let r = late_arg_as_bound_arg(self.tcx, &pair.1, param);
(pair, r)
})
.unzip();
deny_non_region_late_bound(self.tcx, &mut bound_vars, "function pointer types");
self.record_late_bound_vars(ty.hir_id, binders);
let scope = Scope::Binder {
hir_id: ty.hir_id,
bound_vars,
s: self.scope,
scope_type: BinderScopeType::Normal,
where_bound_origin: None,
};
self.with(scope, |this| {
// a bare fn has no bounds, so everything
// contained within is scoped within its binder.
intravisit::walk_ty(this, ty);
});
}
hir::TyKind::TraitObject(bounds, lifetime, _) => {
debug!(?bounds, ?lifetime, "TraitObject");
let scope = Scope::TraitRefBoundary { s: self.scope };
self.with(scope, |this| {
for bound in bounds {
this.visit_poly_trait_ref_inner(
bound,
NonLifetimeBinderAllowed::Deny("trait object types"),
);
}
});
match lifetime.res {
LifetimeName::ImplicitObjectLifetimeDefault => {
// If the user does not write *anything*, we
// use the object lifetime defaulting
// rules. So e.g., `Box<dyn Debug>` becomes
// `Box<dyn Debug + 'static>`.
self.resolve_object_lifetime_default(lifetime)
}
LifetimeName::Infer => {
// If the user writes `'_`, we use the *ordinary* elision
// rules. So the `'_` in e.g., `Box<dyn Debug + '_>` will be
// resolved the same as the `'_` in `&'_ Foo`.
//
// cc #48468
}
LifetimeName::Param(..) | LifetimeName::Static => {
// If the user wrote an explicit name, use that.
self.visit_lifetime(lifetime);
}
LifetimeName::Error => {}
}
}
hir::TyKind::Ref(lifetime_ref, ref mt) => {
self.visit_lifetime(lifetime_ref);
let scope = Scope::ObjectLifetimeDefault {
lifetime: self.map.defs.get(&lifetime_ref.hir_id).cloned(),
s: self.scope,
};
self.with(scope, |this| this.visit_ty(mt.ty));
}
hir::TyKind::OpaqueDef(item_id, lifetimes, _in_trait) => {
// Resolve the lifetimes in the bounds to the lifetime defs in the generics.
// `fn foo<'a>() -> impl MyTrait<'a> { ... }` desugars to
// `type MyAnonTy<'b> = impl MyTrait<'b>;`
// ^ ^ this gets resolved in the scope of
// the opaque_ty generics
let opaque_ty = self.tcx.hir().item(item_id);
match &opaque_ty.kind {
hir::ItemKind::OpaqueTy(hir::OpaqueTy { origin: _, .. }) => {}
i => bug!("`impl Trait` pointed to non-opaque type?? {:#?}", i),
};
// Resolve the lifetimes that are applied to the opaque type.
// These are resolved in the current scope.
// `fn foo<'a>() -> impl MyTrait<'a> { ... }` desugars to
// `fn foo<'a>() -> MyAnonTy<'a> { ... }`
// ^ ^this gets resolved in the current scope
for lifetime in lifetimes {
let hir::GenericArg::Lifetime(lifetime) = lifetime else { continue };
self.visit_lifetime(lifetime);
// Check for predicates like `impl for<'a> Trait<impl OtherTrait<'a>>`
// and ban them. Type variables instantiated inside binders aren't
// well-supported at the moment, so this doesn't work.
// In the future, this should be fixed and this error should be removed.
let def = self.map.defs.get(&lifetime.hir_id).copied();
let Some(ResolvedArg::LateBound(_, _, lifetime_def_id)) = def else { continue };
let Some(lifetime_def_id) = lifetime_def_id.as_local() else { continue };
let lifetime_hir_id = self.tcx.local_def_id_to_hir_id(lifetime_def_id);
let bad_place = match self.tcx.hir_node(self.tcx.parent_hir_id(lifetime_hir_id))
{
// Opaques do not declare their own lifetimes, so if a lifetime comes from an opaque
// it must be a reified late-bound lifetime from a trait goal.
hir::Node::Item(hir::Item {
kind: hir::ItemKind::OpaqueTy { .. }, ..
}) => "higher-ranked lifetime from outer `impl Trait`",
// Other items are fine.
hir::Node::Item(_) | hir::Node::TraitItem(_) | hir::Node::ImplItem(_) => {
continue;
}
hir::Node::Ty(hir::Ty { kind: hir::TyKind::BareFn(_), .. }) => {
"higher-ranked lifetime from function pointer"
}
hir::Node::Ty(hir::Ty { kind: hir::TyKind::TraitObject(..), .. }) => {
"higher-ranked lifetime from `dyn` type"
}
_ => "higher-ranked lifetime",
};
let (span, label) = if lifetime.ident.span == self.tcx.def_span(lifetime_def_id)
{
let opaque_span = self.tcx.def_span(item_id.owner_id);
(opaque_span, Some(opaque_span))
} else {
(lifetime.ident.span, None)
};
// Ensure that the parent of the def is an item, not HRTB
self.tcx.dcx().emit_err(errors::OpaqueCapturesHigherRankedLifetime {
span,
label,
decl_span: self.tcx.def_span(lifetime_def_id),
bad_place,
});
self.uninsert_lifetime_on_error(lifetime, def.unwrap());
}
}
_ => intravisit::walk_ty(self, ty),
}
}
#[instrument(level = "debug", skip(self))]
fn visit_pattern_type_pattern(&mut self, p: &'tcx hir::Pat<'tcx>) {
intravisit::walk_pat(self, p)
}
#[instrument(level = "debug", skip(self))]
fn visit_trait_item(&mut self, trait_item: &'tcx hir::TraitItem<'tcx>) {
use self::hir::TraitItemKind::*;
match trait_item.kind {
Fn(_, _) => {
self.visit_early_late(trait_item.hir_id(), trait_item.generics, |this| {
intravisit::walk_trait_item(this, trait_item)
});
}
Type(bounds, ty) => {
self.visit_early(trait_item.hir_id(), trait_item.generics, |this| {
this.visit_generics(trait_item.generics);
for bound in bounds {
this.visit_param_bound(bound);
}
if let Some(ty) = ty {
this.visit_ty(ty);
}
})
}
Const(_, _) => self.visit_early(trait_item.hir_id(), trait_item.generics, |this| {
intravisit::walk_trait_item(this, trait_item)
}),
}
}
#[instrument(level = "debug", skip(self))]
fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem<'tcx>) {
use self::hir::ImplItemKind::*;
match impl_item.kind {
Fn(..) => self.visit_early_late(impl_item.hir_id(), impl_item.generics, |this| {
intravisit::walk_impl_item(this, impl_item)
}),
Type(ty) => self.visit_early(impl_item.hir_id(), impl_item.generics, |this| {
this.visit_generics(impl_item.generics);
this.visit_ty(ty);
}),
Const(_, _) => self.visit_early(impl_item.hir_id(), impl_item.generics, |this| {
intravisit::walk_impl_item(this, impl_item)
}),
}
}
#[instrument(level = "debug", skip(self))]
fn visit_lifetime(&mut self, lifetime_ref: &'tcx hir::Lifetime) {
match lifetime_ref.res {
hir::LifetimeName::Static => {
self.insert_lifetime(lifetime_ref, ResolvedArg::StaticLifetime)
}
hir::LifetimeName::Param(param_def_id) => {
self.resolve_lifetime_ref(param_def_id, lifetime_ref)
}
// If we've already reported an error, just ignore `lifetime_ref`.
hir::LifetimeName::Error => {}
// Those will be resolved by typechecking.
hir::LifetimeName::ImplicitObjectLifetimeDefault | hir::LifetimeName::Infer => {}
}
}
fn visit_path(&mut self, path: &hir::Path<'tcx>, hir_id: HirId) {
for (i, segment) in path.segments.iter().enumerate() {
let depth = path.segments.len() - i - 1;
if let Some(args) = segment.args {
self.visit_segment_args(path.res, depth, args);
}
}
if let Res::Def(DefKind::TyParam | DefKind::ConstParam, param_def_id) = path.res {
self.resolve_type_ref(param_def_id.expect_local(), hir_id);
}
}
fn visit_fn(
&mut self,
fk: intravisit::FnKind<'tcx>,
fd: &'tcx hir::FnDecl<'tcx>,
body_id: hir::BodyId,
_: Span,
def_id: LocalDefId,
) {
let output = match fd.output {
hir::FnRetTy::DefaultReturn(_) => None,
hir::FnRetTy::Return(ty) => Some(ty),
};
if let Some(ty) = output
&& let hir::TyKind::InferDelegation(sig_id, _) = ty.kind
{
let bound_vars: Vec<_> =
self.tcx.fn_sig(sig_id).skip_binder().bound_vars().iter().collect();
let hir_id = self.tcx.local_def_id_to_hir_id(def_id);
self.map.late_bound_vars.insert(hir_id, bound_vars);
}
self.visit_fn_like_elision(fd.inputs, output, matches!(fk, intravisit::FnKind::Closure));
intravisit::walk_fn_kind(self, fk);
self.visit_nested_body(body_id)
}
fn visit_generics(&mut self, generics: &'tcx hir::Generics<'tcx>) {
let scope = Scope::TraitRefBoundary { s: self.scope };
self.with(scope, |this| {
walk_list!(this, visit_generic_param, generics.params);
walk_list!(this, visit_where_predicate, generics.predicates);
})
}
fn visit_where_predicate(&mut self, predicate: &'tcx hir::WherePredicate<'tcx>) {
match predicate {
&hir::WherePredicate::BoundPredicate(hir::WhereBoundPredicate {
hir_id,
bounded_ty,
bounds,
bound_generic_params,
origin,
..
}) => {
let (bound_vars, binders): (FxIndexMap<LocalDefId, ResolvedArg>, Vec<_>) =
bound_generic_params
.iter()
.enumerate()
.map(|(late_bound_idx, param)| {
let pair = ResolvedArg::late(late_bound_idx as u32, param);
let r = late_arg_as_bound_arg(self.tcx, &pair.1, param);
(pair, r)
})
.unzip();
self.record_late_bound_vars(hir_id, binders);
// Even if there are no lifetimes defined here, we still wrap it in a binder
// scope. If there happens to be a nested poly trait ref (an error), that
// will be `Concatenating` anyways, so we don't have to worry about the depth
// being wrong.
let scope = Scope::Binder {
hir_id,
bound_vars,
s: self.scope,
scope_type: BinderScopeType::Normal,
where_bound_origin: Some(origin),
};
self.with(scope, |this| {
walk_list!(this, visit_generic_param, bound_generic_params);
this.visit_ty(bounded_ty);
walk_list!(this, visit_param_bound, bounds);
})
}
&hir::WherePredicate::RegionPredicate(hir::WhereRegionPredicate {
lifetime,
bounds,
..
}) => {
self.visit_lifetime(lifetime);
walk_list!(self, visit_param_bound, bounds);
}
&hir::WherePredicate::EqPredicate(hir::WhereEqPredicate { lhs_ty, rhs_ty, .. }) => {
self.visit_ty(lhs_ty);
self.visit_ty(rhs_ty);
}
}
}
fn visit_poly_trait_ref(&mut self, trait_ref: &'tcx hir::PolyTraitRef<'tcx>) {
self.visit_poly_trait_ref_inner(trait_ref, NonLifetimeBinderAllowed::Allow);
}
fn visit_anon_const(&mut self, c: &'tcx hir::AnonConst) {
self.with(Scope::LateBoundary { s: self.scope, what: "constant" }, |this| {
intravisit::walk_anon_const(this, c);
});
}
fn visit_generic_param(&mut self, p: &'tcx GenericParam<'tcx>) {
match p.kind {
GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
self.resolve_type_ref(p.def_id, p.hir_id);
}
GenericParamKind::Lifetime { .. } => {
// No need to resolve lifetime params, we don't use them for things
// like implicit `?Sized` or const-param-has-ty predicates.
}
}
match p.kind {
GenericParamKind::Lifetime { .. } => {}
GenericParamKind::Type { default, .. } => {
if let Some(ty) = default {
self.visit_ty(ty);
}
}
GenericParamKind::Const { ty, default, is_host_effect: _ } => {
self.visit_ty(ty);
if let Some(default) = default {
self.visit_body(self.tcx.hir().body(default.body));
}
}
}
}
}
fn object_lifetime_default(tcx: TyCtxt<'_>, param_def_id: LocalDefId) -> ObjectLifetimeDefault {
debug_assert_eq!(tcx.def_kind(param_def_id), DefKind::TyParam);
let hir::Node::GenericParam(param) = tcx.hir_node_by_def_id(param_def_id) else {
bug!("expected GenericParam for object_lifetime_default");
};
match param.source {
hir::GenericParamSource::Generics => {
let parent_def_id = tcx.local_parent(param_def_id);
let generics = tcx.hir().get_generics(parent_def_id).unwrap();
let param_hir_id = tcx.local_def_id_to_hir_id(param_def_id);
let param = generics.params.iter().find(|p| p.hir_id == param_hir_id).unwrap();
// Scan the bounds and where-clauses on parameters to extract bounds
// of the form `T:'a` so as to determine the `ObjectLifetimeDefault`
// for each type parameter.
match param.kind {
GenericParamKind::Type { .. } => {
let mut set = Set1::Empty;
// Look for `type: ...` where clauses.
for bound in generics.bounds_for_param(param_def_id) {
// Ignore `for<'a> type: ...` as they can change what
// lifetimes mean (although we could "just" handle it).
if !bound.bound_generic_params.is_empty() {
continue;
}
for bound in bound.bounds {
if let hir::GenericBound::Outlives(lifetime) = bound {
set.insert(lifetime.res);
}
}
}
match set {
Set1::Empty => ObjectLifetimeDefault::Empty,
Set1::One(hir::LifetimeName::Static) => ObjectLifetimeDefault::Static,
Set1::One(hir::LifetimeName::Param(param_def_id)) => {
ObjectLifetimeDefault::Param(param_def_id.to_def_id())
}
_ => ObjectLifetimeDefault::Ambiguous,
}
}
_ => {
bug!("object_lifetime_default_raw must only be called on a type parameter")
}
}
}
hir::GenericParamSource::Binder => ObjectLifetimeDefault::Empty,
}
}
impl<'a, 'tcx> BoundVarContext<'a, 'tcx> {
fn with<F>(&mut self, wrap_scope: Scope<'_>, f: F)
where
F: for<'b> FnOnce(&mut BoundVarContext<'b, 'tcx>),
{
let BoundVarContext { tcx, map, .. } = self;
let mut this = BoundVarContext { tcx: *tcx, map, scope: &wrap_scope };
let span = debug_span!("scope", scope = ?TruncatedScopeDebug(this.scope));
{
let _enter = span.enter();
f(&mut this);
}
}
fn record_late_bound_vars(&mut self, hir_id: HirId, binder: Vec<ty::BoundVariableKind>) {
if let Some(old) = self.map.late_bound_vars.insert(hir_id, binder) {
bug!(
"overwrote bound vars for {hir_id:?}:\nold={old:?}\nnew={:?}",
self.map.late_bound_vars[&hir_id]
)
}
}
/// Visits self by adding a scope and handling recursive walk over the contents with `walk`.
///
/// Handles visiting fns and methods. These are a bit complicated because we must distinguish
/// early- vs late-bound lifetime parameters. We do this by checking which lifetimes appear
/// within type bounds; those are early bound lifetimes, and the rest are late bound.
///
/// For example:
///
/// fn foo<'a,'b,'c,T:Trait<'b>>(...)
///
/// Here `'a` and `'c` are late bound but `'b` is early bound. Note that early- and late-bound
/// lifetimes may be interspersed together.
///
/// If early bound lifetimes are present, we separate them into their own list (and likewise
/// for late bound). They will be numbered sequentially, starting from the lowest index that is
/// already in scope (for a fn item, that will be 0, but for a method it might not be). Late
/// bound lifetimes are resolved by name and associated with a binder ID (`binder_id`), so the
/// ordering is not important there.
fn visit_early_late<F>(&mut self, hir_id: HirId, generics: &'tcx hir::Generics<'tcx>, walk: F)
where
F: for<'b, 'c> FnOnce(&'b mut BoundVarContext<'c, 'tcx>),
{
let mut named_late_bound_vars = 0;
let bound_vars: FxIndexMap<LocalDefId, ResolvedArg> = generics
.params
.iter()
.map(|param| match param.kind {
GenericParamKind::Lifetime { .. } => {
if self.tcx.is_late_bound(param.hir_id) {
let late_bound_idx = named_late_bound_vars;
named_late_bound_vars += 1;
ResolvedArg::late(late_bound_idx, param)
} else {
ResolvedArg::early(param)
}
}
GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
ResolvedArg::early(param)
}
})
.collect();
let binders: Vec<_> = generics
.params
.iter()
.filter(|param| {
matches!(param.kind, GenericParamKind::Lifetime { .. })
&& self.tcx.is_late_bound(param.hir_id)
})
.enumerate()
.map(|(late_bound_idx, param)| {
let pair = ResolvedArg::late(late_bound_idx as u32, param);
late_arg_as_bound_arg(self.tcx, &pair.1, param)
})
.collect();
self.record_late_bound_vars(hir_id, binders);
let scope = Scope::Binder {
hir_id,
bound_vars,
s: self.scope,
scope_type: BinderScopeType::Normal,
where_bound_origin: None,
};
self.with(scope, walk);
}
fn visit_early<F>(&mut self, hir_id: HirId, generics: &'tcx hir::Generics<'tcx>, walk: F)
where
F: for<'b, 'c> FnOnce(&'b mut BoundVarContext<'c, 'tcx>),
{
let bound_vars = generics.params.iter().map(ResolvedArg::early).collect();
self.record_late_bound_vars(hir_id, vec![]);
let scope = Scope::Binder {
hir_id,
bound_vars,
s: self.scope,
scope_type: BinderScopeType::Normal,
where_bound_origin: None,
};
self.with(scope, |this| {
let scope = Scope::TraitRefBoundary { s: this.scope };
this.with(scope, walk)
});
}
#[instrument(level = "debug", skip(self))]
fn resolve_lifetime_ref(
&mut self,
region_def_id: LocalDefId,
lifetime_ref: &'tcx hir::Lifetime,
) {
// Walk up the scope chain, tracking the number of fn scopes
// that we pass through, until we find a lifetime with the
// given name or we run out of scopes.
// search.
let mut late_depth = 0;
let mut scope = self.scope;
let mut outermost_body = None;
let mut crossed_late_boundary = None;
let result = loop {
match *scope {
Scope::Body { id, s } => {
outermost_body = Some(id);
scope = s;
}
Scope::Root { opt_parent_item } => {
if let Some(parent_item) = opt_parent_item
&& let parent_generics = self.tcx.generics_of(parent_item)
&& parent_generics
.param_def_id_to_index(self.tcx, region_def_id.to_def_id())
.is_some()
{
break Some(ResolvedArg::EarlyBound(region_def_id.to_def_id()));
}
break None;
}
Scope::Binder { ref bound_vars, scope_type, s, where_bound_origin, .. } => {
if let Some(&def) = bound_vars.get(®ion_def_id) {
break Some(def.shifted(late_depth));
}
match scope_type {
BinderScopeType::Normal => late_depth += 1,
BinderScopeType::Concatenating => {}
}
// Fresh lifetimes in APIT used to be allowed in async fns and forbidden in
// regular fns.
if let Some(hir::PredicateOrigin::ImplTrait) = where_bound_origin
&& let hir::LifetimeName::Param(param_id) = lifetime_ref.res
&& let Some(generics) =
self.tcx.hir().get_generics(self.tcx.local_parent(param_id))
&& let Some(param) = generics.params.iter().find(|p| p.def_id == param_id)
&& param.is_elided_lifetime()
&& !self.tcx.asyncness(lifetime_ref.hir_id.owner.def_id).is_async()
&& !self.tcx.features().anonymous_lifetime_in_impl_trait
{
let mut diag: rustc_errors::Diag<'_> = rustc_session::parse::feature_err(
&self.tcx.sess,
sym::anonymous_lifetime_in_impl_trait,
lifetime_ref.ident.span,
"anonymous lifetimes in `impl Trait` are unstable",
);
if let Some(generics) =
self.tcx.hir().get_generics(lifetime_ref.hir_id.owner.def_id)
{
let new_param_sugg =
if let Some(span) = generics.span_for_lifetime_suggestion() {
(span, "'a, ".to_owned())
} else {
(generics.span, "<'a>".to_owned())
};
let lifetime_sugg = match lifetime_ref.suggestion_position() {
(hir::LifetimeSuggestionPosition::Normal, span) => {
(span, "'a".to_owned())
}
(hir::LifetimeSuggestionPosition::Ampersand, span) => {
(span, "'a ".to_owned())
}
(hir::LifetimeSuggestionPosition::ElidedPath, span) => {
(span, "<'a>".to_owned())
}
(hir::LifetimeSuggestionPosition::ElidedPathArgument, span) => {
(span, "'a, ".to_owned())
}
(hir::LifetimeSuggestionPosition::ObjectDefault, span) => {
(span, "+ 'a".to_owned())
}
};
let suggestions = vec![lifetime_sugg, new_param_sugg];
diag.span_label(
lifetime_ref.ident.span,
"expected named lifetime parameter",
);
diag.multipart_suggestion(
"consider introducing a named lifetime parameter",
suggestions,
rustc_errors::Applicability::MaybeIncorrect,
);
}
diag.emit();
return;
}
scope = s;
}
Scope::ObjectLifetimeDefault { s, .. }
| Scope::Supertrait { s, .. }
| Scope::TraitRefBoundary { s, .. } => {
scope = s;
}
Scope::LateBoundary { s, what } => {
crossed_late_boundary = Some(what);
scope = s;
}
}
};
if let Some(mut def) = result {
if let ResolvedArg::EarlyBound(..) = def {
// Do not free early-bound regions, only late-bound ones.
} else if let ResolvedArg::LateBound(_, _, param_def_id) = def
&& let Some(what) = crossed_late_boundary
{
let use_span = lifetime_ref.ident.span;
let def_span = self.tcx.def_span(param_def_id);
let guar = match self.tcx.def_kind(param_def_id) {
DefKind::LifetimeParam => {
self.tcx.dcx().emit_err(errors::CannotCaptureLateBound::Lifetime {
use_span,
def_span,
what,
})
}
kind => span_bug!(
use_span,
"did not expect to resolve lifetime to {}",
kind.descr(param_def_id)
),
};
def = ResolvedArg::Error(guar);
} else if let Some(body_id) = outermost_body {
let fn_id = self.tcx.hir().body_owner(body_id);
match self.tcx.hir_node(fn_id) {
Node::Item(hir::Item { owner_id, kind: hir::ItemKind::Fn(..), .. })
| Node::TraitItem(hir::TraitItem {
owner_id,
kind: hir::TraitItemKind::Fn(..),
..
})
| Node::ImplItem(hir::ImplItem {
owner_id,
kind: hir::ImplItemKind::Fn(..),
..
}) => {
def = ResolvedArg::Free(owner_id.to_def_id(), def.id().unwrap());
}
Node::Expr(hir::Expr { kind: hir::ExprKind::Closure(closure), .. }) => {
def = ResolvedArg::Free(closure.def_id.to_def_id(), def.id().unwrap());
}
_ => {}
}
}
self.insert_lifetime(lifetime_ref, def);
return;
}
// We may fail to resolve higher-ranked lifetimes that are mentioned by APIT.
// AST-based resolution does not care for impl-trait desugaring, which are the
// responsibility of lowering. This may create a mismatch between the resolution
// AST found (`region_def_id`) which points to HRTB, and what HIR allows.
// ```
// fn foo(x: impl for<'a> Trait<'a, Assoc = impl Copy + 'a>) {}
// ```
//
// In such case, walk back the binders to diagnose it properly.
let mut scope = self.scope;
loop {
match *scope {
Scope::Binder {
where_bound_origin: Some(hir::PredicateOrigin::ImplTrait), ..
} => {
self.tcx.dcx().emit_err(errors::LateBoundInApit::Lifetime {
span: lifetime_ref.ident.span,
param_span: self.tcx.def_span(region_def_id),
});
return;
}
Scope::Root { .. } => break,
Scope::Binder { s, .. }
| Scope::Body { s, .. }
| Scope::ObjectLifetimeDefault { s, .. }
| Scope::Supertrait { s, .. }
| Scope::TraitRefBoundary { s, .. }
| Scope::LateBoundary { s, .. } => {
scope = s;
}
}
}
self.tcx.dcx().span_delayed_bug(
lifetime_ref.ident.span,
format!("Could not resolve {:?} in scope {:#?}", lifetime_ref, self.scope,),
);
}
fn resolve_type_ref(&mut self, param_def_id: LocalDefId, hir_id: HirId) {
// Walk up the scope chain, tracking the number of fn scopes
// that we pass through, until we find a lifetime with the
// given name or we run out of scopes.
// search.
let mut late_depth = 0;
let mut scope = self.scope;
let mut crossed_late_boundary = None;
let result = loop {
match *scope {
Scope::Body { s, .. } => {
scope = s;
}
Scope::Root { opt_parent_item } => {
if let Some(parent_item) = opt_parent_item
&& let parent_generics = self.tcx.generics_of(parent_item)
&& parent_generics
.param_def_id_to_index(self.tcx, param_def_id.to_def_id())
.is_some()
{
break Some(ResolvedArg::EarlyBound(param_def_id.to_def_id()));
}
break None;
}
Scope::Binder { ref bound_vars, scope_type, s, .. } => {
if let Some(&def) = bound_vars.get(¶m_def_id) {
break Some(def.shifted(late_depth));
}
match scope_type {
BinderScopeType::Normal => late_depth += 1,
BinderScopeType::Concatenating => {}
}
scope = s;
}
Scope::ObjectLifetimeDefault { s, .. }
| Scope::Supertrait { s, .. }
| Scope::TraitRefBoundary { s, .. } => {
scope = s;
}
Scope::LateBoundary { s, what } => {
crossed_late_boundary = Some(what);
scope = s;
}
}
};
if let Some(def) = result {
if let ResolvedArg::LateBound(..) = def
&& let Some(what) = crossed_late_boundary
{
let use_span = self.tcx.hir().span(hir_id);
let def_span = self.tcx.def_span(param_def_id);
let guar = match self.tcx.def_kind(param_def_id) {
DefKind::ConstParam => {
self.tcx.dcx().emit_err(errors::CannotCaptureLateBound::Const {
use_span,
def_span,
what,
})
}
DefKind::TyParam => {
self.tcx.dcx().emit_err(errors::CannotCaptureLateBound::Type {
use_span,
def_span,
what,
})
}
kind => span_bug!(
use_span,
"did not expect to resolve non-lifetime param to {}",
kind.descr(param_def_id.to_def_id())
),
};
self.map.defs.insert(hir_id, ResolvedArg::Error(guar));
} else {
self.map.defs.insert(hir_id, def);
}
return;
}
// We may fail to resolve higher-ranked ty/const vars that are mentioned by APIT.
// AST-based resolution does not care for impl-trait desugaring, which are the
// responsibility of lowering. This may create a mismatch between the resolution
// AST found (`param_def_id`) which points to HRTB, and what HIR allows.
// ```
// fn foo(x: impl for<T> Trait<Assoc = impl Trait2<T>>) {}
// ```
//
// In such case, walk back the binders to diagnose it properly.
let mut scope = self.scope;
loop {
match *scope {
Scope::Binder {
where_bound_origin: Some(hir::PredicateOrigin::ImplTrait), ..
} => {
let guar = self.tcx.dcx().emit_err(match self.tcx.def_kind(param_def_id) {
DefKind::TyParam => errors::LateBoundInApit::Type {
span: self.tcx.hir().span(hir_id),
param_span: self.tcx.def_span(param_def_id),
},
DefKind::ConstParam => errors::LateBoundInApit::Const {
span: self.tcx.hir().span(hir_id),
param_span: self.tcx.def_span(param_def_id),
},
kind => {
bug!("unexpected def-kind: {}", kind.descr(param_def_id.to_def_id()))
}
});
self.map.defs.insert(hir_id, ResolvedArg::Error(guar));
return;
}
Scope::Root { .. } => break,
Scope::Binder { s, .. }
| Scope::Body { s, .. }
| Scope::ObjectLifetimeDefault { s, .. }
| Scope::Supertrait { s, .. }
| Scope::TraitRefBoundary { s, .. }
| Scope::LateBoundary { s, .. } => {
scope = s;
}
}
}
self.tcx
.dcx()
.span_bug(self.tcx.hir().span(hir_id), format!("could not resolve {param_def_id:?}"));
}
#[instrument(level = "debug", skip(self))]
fn visit_segment_args(
&mut self,
res: Res,
depth: usize,
generic_args: &'tcx hir::GenericArgs<'tcx>,
) {
if generic_args.parenthesized == hir::GenericArgsParentheses::ParenSugar {
self.visit_fn_like_elision(
generic_args.inputs(),
Some(generic_args.bindings[0].ty()),
false,
);
return;
}
for arg in generic_args.args {
if let hir::GenericArg::Lifetime(lt) = arg {
self.visit_lifetime(lt);
}
}
// Figure out if this is a type/trait segment,
// which requires object lifetime defaults.
let type_def_id = match res {
Res::Def(DefKind::AssocTy, def_id) if depth == 1 => Some(self.tcx.parent(def_id)),
Res::Def(DefKind::Variant, def_id) if depth == 0 => Some(self.tcx.parent(def_id)),
Res::Def(
DefKind::Struct
| DefKind::Union
| DefKind::Enum
| DefKind::TyAlias
| DefKind::Trait,
def_id,
) if depth == 0 => Some(def_id),
_ => None,
};
debug!(?type_def_id);
// Compute a vector of defaults, one for each type parameter,
// per the rules given in RFCs 599 and 1156. Example:
//
// ```rust
// struct Foo<'a, T: 'a, U> { }
// ```
//
// If you have `Foo<'x, dyn Bar, dyn Baz>`, we want to default
// `dyn Bar` to `dyn Bar + 'x` (because of the `T: 'a` bound)
// and `dyn Baz` to `dyn Baz + 'static` (because there is no
// such bound).
//
// Therefore, we would compute `object_lifetime_defaults` to a
// vector like `['x, 'static]`. Note that the vector only
// includes type parameters.
let object_lifetime_defaults = type_def_id.map_or_else(Vec::new, |def_id| {
let in_body = {
let mut scope = self.scope;
loop {
match *scope {
Scope::Root { .. } => break false,
Scope::Body { .. } => break true,
Scope::Binder { s, .. }
| Scope::ObjectLifetimeDefault { s, .. }
| Scope::Supertrait { s, .. }
| Scope::TraitRefBoundary { s, .. }
| Scope::LateBoundary { s, .. } => {
scope = s;
}
}
}
};
let map = &self.map;
let generics = self.tcx.generics_of(def_id);
// `type_def_id` points to an item, so there is nothing to inherit generics from.
debug_assert_eq!(generics.parent_count, 0);
let set_to_region = |set: ObjectLifetimeDefault| match set {
ObjectLifetimeDefault::Empty => {
if in_body {
None
} else {
Some(ResolvedArg::StaticLifetime)
}
}
ObjectLifetimeDefault::Static => Some(ResolvedArg::StaticLifetime),
ObjectLifetimeDefault::Param(param_def_id) => {
// This index can be used with `generic_args` since `parent_count == 0`.
let index = generics.param_def_id_to_index[¶m_def_id] as usize;
generic_args.args.get(index).and_then(|arg| match arg {
GenericArg::Lifetime(lt) => map.defs.get(<.hir_id).copied(),
_ => None,
})
}
ObjectLifetimeDefault::Ambiguous => None,
};
generics
.params
.iter()
.filter_map(|param| {
match self.tcx.def_kind(param.def_id) {
// Generic consts don't impose any constraints.
//
// We still store a dummy value here to allow generic parameters
// in an arbitrary order.
DefKind::ConstParam => Some(ObjectLifetimeDefault::Empty),
DefKind::TyParam => Some(self.tcx.object_lifetime_default(param.def_id)),
// We may also get a `Trait` or `TraitAlias` because of how generics `Self` parameter
// works. Ignore it because it can't have a meaningful lifetime default.
DefKind::LifetimeParam | DefKind::Trait | DefKind::TraitAlias => None,
dk => bug!("unexpected def_kind {:?}", dk),
}
})
.map(set_to_region)
.collect()
});
debug!(?object_lifetime_defaults);
let mut i = 0;
for arg in generic_args.args {
match arg {
GenericArg::Lifetime(_) => {}
GenericArg::Type(ty) => {
if let Some(<) = object_lifetime_defaults.get(i) {
let scope = Scope::ObjectLifetimeDefault { lifetime: lt, s: self.scope };
self.with(scope, |this| this.visit_ty(ty));
} else {
self.visit_ty(ty);
}
i += 1;
}
GenericArg::Const(ct) => {
self.visit_anon_const(&ct.value);
i += 1;
}
GenericArg::Infer(inf) => {
self.visit_id(inf.hir_id);
i += 1;
}
}
}
// Hack: when resolving the type `XX` in binding like `dyn
// Foo<'b, Item = XX>`, the current object-lifetime default
// would be to examine the trait `Foo` to check whether it has
// a lifetime bound declared on `Item`. e.g., if `Foo` is
// declared like so, then the default object lifetime bound in
// `XX` should be `'b`:
//
// ```rust
// trait Foo<'a> {
// type Item: 'a;
// }
// ```
//
// but if we just have `type Item;`, then it would be
// `'static`. However, we don't get all of this logic correct.
//
// Instead, we do something hacky: if there are no lifetime parameters
// to the trait, then we simply use a default object lifetime
// bound of `'static`, because there is no other possibility. On the other hand,
// if there ARE lifetime parameters, then we require the user to give an
// explicit bound for now.
//
// This is intended to leave room for us to implement the
// correct behavior in the future.
let has_lifetime_parameter =
generic_args.args.iter().any(|arg| matches!(arg, GenericArg::Lifetime(_)));
// Resolve lifetimes found in the bindings, so either in the type `XX` in `Item = XX` or
// in the trait ref `YY<...>` in `Item: YY<...>`.
for binding in generic_args.bindings {
let scope = Scope::ObjectLifetimeDefault {
lifetime: if has_lifetime_parameter {
None
} else {
Some(ResolvedArg::StaticLifetime)
},
s: self.scope,
};
// If the binding is parenthesized, then this must be `feature(return_type_notation)`.
// In that case, introduce a binder over all of the function's early and late bound vars.
//
// For example, given
// ```
// trait Foo {
// async fn x<'r, T>();
// }
// ```
// and a bound that looks like:
// `for<'a> T::Trait<'a, x(): for<'b> Other<'b>>`
// this is going to expand to something like:
// `for<'a> for<'r, T> <T as Trait<'a>>::x::<'r, T>::{opaque#0}: for<'b> Other<'b>`.
if binding.gen_args.parenthesized == hir::GenericArgsParentheses::ReturnTypeNotation {
let bound_vars = if let Some(type_def_id) = type_def_id
&& self.tcx.def_kind(type_def_id) == DefKind::Trait
&& let Some((mut bound_vars, assoc_fn)) = BoundVarContext::supertrait_hrtb_vars(
self.tcx,
type_def_id,
binding.ident,
ty::AssocKind::Fn,
) {
bound_vars.extend(self.tcx.generics_of(assoc_fn.def_id).params.iter().map(
|param| match param.kind {
ty::GenericParamDefKind::Lifetime => ty::BoundVariableKind::Region(
ty::BoundRegionKind::BrNamed(param.def_id, param.name),
),
ty::GenericParamDefKind::Type { .. } => ty::BoundVariableKind::Ty(
ty::BoundTyKind::Param(param.def_id, param.name),
),
ty::GenericParamDefKind::Const { .. } => ty::BoundVariableKind::Const,
},
));
bound_vars.extend(
self.tcx.fn_sig(assoc_fn.def_id).instantiate_identity().bound_vars(),
);
bound_vars
} else {
self.tcx
.dcx()
.span_delayed_bug(binding.ident.span, "bad return type notation here");
vec![]
};
self.with(scope, |this| {
let scope = Scope::Supertrait { bound_vars, s: this.scope };
this.with(scope, |this| {
let (bound_vars, _) = this.poly_trait_ref_binder_info();
this.record_late_bound_vars(binding.hir_id, bound_vars);
this.visit_assoc_type_binding(binding)
});
});
} else if let Some(type_def_id) = type_def_id {
let bound_vars = BoundVarContext::supertrait_hrtb_vars(
self.tcx,
type_def_id,
binding.ident,
ty::AssocKind::Type,
)
.map(|(bound_vars, _)| bound_vars);
self.with(scope, |this| {
let scope = Scope::Supertrait {
bound_vars: bound_vars.unwrap_or_default(),
s: this.scope,
};
this.with(scope, |this| this.visit_assoc_type_binding(binding));
});
} else {
self.with(scope, |this| this.visit_assoc_type_binding(binding));
}
}
}
/// Returns all the late-bound vars that come into scope from supertrait HRTBs, based on the
/// associated type name and starting trait.
/// For example, imagine we have
/// ```ignore (illustrative)
/// trait Foo<'a, 'b> {
/// type As;
/// }
/// trait Bar<'b>: for<'a> Foo<'a, 'b> {}
/// trait Bar: for<'b> Bar<'b> {}
/// ```
/// In this case, if we wanted to the supertrait HRTB lifetimes for `As` on
/// the starting trait `Bar`, we would return `Some(['b, 'a])`.
fn supertrait_hrtb_vars(
tcx: TyCtxt<'tcx>,
def_id: DefId,
assoc_name: Ident,
assoc_kind: ty::AssocKind,
) -> Option<(Vec<ty::BoundVariableKind>, &'tcx ty::AssocItem)> {
let trait_defines_associated_item_named = |trait_def_id: DefId| {
tcx.associated_items(trait_def_id).find_by_name_and_kind(
tcx,
assoc_name,
assoc_kind,
trait_def_id,
)
};
use smallvec::{smallvec, SmallVec};
let mut stack: SmallVec<[(DefId, SmallVec<[ty::BoundVariableKind; 8]>); 8]> =
smallvec![(def_id, smallvec![])];
let mut visited: FxHashSet<DefId> = FxHashSet::default();
loop {
let Some((def_id, bound_vars)) = stack.pop() else {
break None;
};
// See issue #83753. If someone writes an associated type on a non-trait, just treat it as
// there being no supertrait HRTBs.
match tcx.def_kind(def_id) {
DefKind::Trait | DefKind::TraitAlias | DefKind::Impl { .. } => {}
_ => break None,
}
if let Some(assoc_item) = trait_defines_associated_item_named(def_id) {
break Some((bound_vars.into_iter().collect(), assoc_item));
}
let predicates = tcx.super_predicates_that_define_assoc_item((def_id, assoc_name));
let obligations = predicates.predicates.iter().filter_map(|&(pred, _)| {
let bound_predicate = pred.kind();
match bound_predicate.skip_binder() {
ty::ClauseKind::Trait(data) => {
// The order here needs to match what we would get from
// `rustc_middle::ty::predicate::Clause::instantiate_supertrait`
let pred_bound_vars = bound_predicate.bound_vars();
let mut all_bound_vars = bound_vars.clone();
all_bound_vars.extend(pred_bound_vars.iter());
let super_def_id = data.trait_ref.def_id;
Some((super_def_id, all_bound_vars))
}
_ => None,
}
});
let obligations = obligations.filter(|o| visited.insert(o.0));
stack.extend(obligations);
}
}
#[instrument(level = "debug", skip(self))]
fn visit_fn_like_elision(
&mut self,
inputs: &'tcx [hir::Ty<'tcx>],
output: Option<&'tcx hir::Ty<'tcx>>,
in_closure: bool,
) {
self.with(
Scope::ObjectLifetimeDefault {
lifetime: Some(ResolvedArg::StaticLifetime),
s: self.scope,
},
|this| {
for input in inputs {
this.visit_ty(input);
}
if !in_closure && let Some(output) = output {
this.visit_ty(output);
}
},
);
if in_closure && let Some(output) = output {
self.visit_ty(output);
}
}
#[instrument(level = "debug", skip(self))]
fn resolve_object_lifetime_default(&mut self, lifetime_ref: &'tcx hir::Lifetime) {
let mut late_depth = 0;
let mut scope = self.scope;
let lifetime = loop {
match *scope {
Scope::Binder { s, scope_type, .. } => {
match scope_type {
BinderScopeType::Normal => late_depth += 1,
BinderScopeType::Concatenating => {}
}
scope = s;
}
Scope::Root { .. } => break ResolvedArg::StaticLifetime,
Scope::Body { .. } | Scope::ObjectLifetimeDefault { lifetime: None, .. } => return,
Scope::ObjectLifetimeDefault { lifetime: Some(l), .. } => break l,
Scope::Supertrait { s, .. }
| Scope::TraitRefBoundary { s, .. }
| Scope::LateBoundary { s, .. } => {
scope = s;
}
}
};
self.insert_lifetime(lifetime_ref, lifetime.shifted(late_depth));
}
#[instrument(level = "debug", skip(self))]
fn insert_lifetime(&mut self, lifetime_ref: &'tcx hir::Lifetime, def: ResolvedArg) {
debug!(span = ?lifetime_ref.ident.span);
self.map.defs.insert(lifetime_ref.hir_id, def);
}
/// Sometimes we resolve a lifetime, but later find that it is an
/// error (esp. around impl trait). In that case, we remove the
/// entry into `map.defs` so as not to confuse later code.
fn uninsert_lifetime_on_error(
&mut self,
lifetime_ref: &'tcx hir::Lifetime,
bad_def: ResolvedArg,
) {
// FIXME(#120456) - is `swap_remove` correct?
let old_value = self.map.defs.swap_remove(&lifetime_ref.hir_id);
assert_eq!(old_value, Some(bad_def));
}
}
/// Detects late-bound lifetimes and inserts them into
/// `late_bound`.
///
/// A region declared on a fn is **late-bound** if:
/// - it is constrained by an argument type;
/// - it does not appear in a where-clause.
///
/// "Constrained" basically means that it appears in any type but
/// not amongst the inputs to a projection. In other words, `<&'a
/// T as Trait<''b>>::Foo` does not constrain `'a` or `'b`.
fn is_late_bound_map(
tcx: TyCtxt<'_>,
owner_id: hir::OwnerId,
) -> Option<&FxIndexSet<hir::ItemLocalId>> {
let decl = tcx.hir().fn_decl_by_hir_id(owner_id.into())?;
let generics = tcx.hir().get_generics(owner_id.def_id)?;
let mut late_bound = FxIndexSet::default();
let mut constrained_by_input = ConstrainedCollector { regions: Default::default(), tcx };
for arg_ty in decl.inputs {
constrained_by_input.visit_ty(arg_ty);
}
let mut appears_in_output = AllCollector::default();
intravisit::walk_fn_ret_ty(&mut appears_in_output, &decl.output);
debug!(?constrained_by_input.regions);
// Walk the lifetimes that appear in where clauses.
//
// Subtle point: because we disallow nested bindings, we can just
// ignore binders here and scrape up all names we see.
let mut appears_in_where_clause = AllCollector::default();
appears_in_where_clause.visit_generics(generics);
debug!(?appears_in_where_clause.regions);
// Late bound regions are those that:
// - appear in the inputs
// - do not appear in the where-clauses
// - are not implicitly captured by `impl Trait`
for param in generics.params {
match param.kind {
hir::GenericParamKind::Lifetime { .. } => { /* fall through */ }
// Neither types nor consts are late-bound.
hir::GenericParamKind::Type { .. } | hir::GenericParamKind::Const { .. } => continue,
}
// appears in the where clauses? early-bound.
if appears_in_where_clause.regions.contains(¶m.def_id) {
continue;
}
// does not appear in the inputs, but appears in the return type? early-bound.
if !constrained_by_input.regions.contains(¶m.def_id)
&& appears_in_output.regions.contains(¶m.def_id)
{
continue;
}
debug!("lifetime {:?} with id {:?} is late-bound", param.name.ident(), param.def_id);
let inserted = late_bound.insert(param.hir_id.local_id);
assert!(inserted, "visited lifetime {:?} twice", param.def_id);
}
debug!(?late_bound);
return Some(tcx.arena.alloc(late_bound));
/// Visits a `ty::Ty` collecting information about what generic parameters are constrained.
///
/// The visitor does not operate on `hir::Ty` so that it can be called on the rhs of a `type Alias<...> = ...;`
/// which may live in a separate crate so there would not be any hir available. Instead we use the `type_of`
/// query to obtain a `ty::Ty` which will be present even in cross crate scenarios. It also naturally
/// handles cycle detection as we go through the query system.
///
/// This is necessary in the first place for the following case:
/// ```rust,ignore (pseudo-Rust)
/// type Alias<'a, T> = <T as Trait<'a>>::Assoc;
/// fn foo<'a>(_: Alias<'a, ()>) -> Alias<'a, ()> { ... }
/// ```
///
/// If we conservatively considered `'a` unconstrained then we could break users who had written code before
/// we started correctly handling aliases. If we considered `'a` constrained then it would become late bound
/// causing an error during HIR ty lowering as the `'a` is not constrained by the input type `<() as Trait<'a>>::Assoc`
/// but appears in the output type `<() as Trait<'a>>::Assoc`.
///
/// We must therefore "look into" the `Alias` to see whether we should consider `'a` constrained or not.
///
/// See #100508 #85533 #47511 for additional context
struct ConstrainedCollectorPostHirTyLowering {
arg_is_constrained: Box<[bool]>,
}
use ty::Ty;
impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for ConstrainedCollectorPostHirTyLowering {
fn visit_ty(&mut self, t: Ty<'tcx>) {
match t.kind() {
ty::Param(param_ty) => {
self.arg_is_constrained[param_ty.index as usize] = true;
}
ty::Alias(ty::Projection | ty::Inherent, _) => return,
_ => (),
}
t.super_visit_with(self)
}
fn visit_const(&mut self, _: ty::Const<'tcx>) {}
fn visit_region(&mut self, r: ty::Region<'tcx>) {
debug!("r={:?}", r.kind());
if let ty::RegionKind::ReEarlyParam(region) = r.kind() {
self.arg_is_constrained[region.index as usize] = true;
}
}
}
struct ConstrainedCollector<'tcx> {
tcx: TyCtxt<'tcx>,
regions: FxHashSet<LocalDefId>,
}
impl<'v> Visitor<'v> for ConstrainedCollector<'_> {
fn visit_ty(&mut self, ty: &'v hir::Ty<'v>) {
match ty.kind {
hir::TyKind::Path(
hir::QPath::Resolved(Some(_), _) | hir::QPath::TypeRelative(..),
) => {
// ignore lifetimes appearing in associated type
// projections, as they are not *constrained*
// (defined above)
}
hir::TyKind::Path(hir::QPath::Resolved(
None,
hir::Path { res: Res::Def(DefKind::TyAlias, alias_def), segments, span },
)) => {
// See comments on `ConstrainedCollectorPostHirTyLowering` for why this arm does not
// just consider args to be unconstrained.
let generics = self.tcx.generics_of(alias_def);
let mut walker = ConstrainedCollectorPostHirTyLowering {
arg_is_constrained: vec![false; generics.params.len()].into_boxed_slice(),
};
walker.visit_ty(self.tcx.type_of(alias_def).instantiate_identity());
match segments.last() {
Some(hir::PathSegment { args: Some(args), .. }) => {
let tcx = self.tcx;
for constrained_arg in
args.args.iter().enumerate().flat_map(|(n, arg)| {
match walker.arg_is_constrained.get(n) {
Some(true) => Some(arg),
Some(false) => None,
None => {
tcx.dcx().span_delayed_bug(
*span,
format!(
"Incorrect generic arg count for alias {alias_def:?}"
),
);
None
}
}
})
{
self.visit_generic_arg(constrained_arg);
}
}
Some(_) => (),
None => bug!("Path with no segments or self type"),
}
}
hir::TyKind::Path(hir::QPath::Resolved(None, path)) => {
// consider only the lifetimes on the final
// segment; I am not sure it's even currently
// valid to have them elsewhere, but even if it
// is, those would be potentially inputs to
// projections
if let Some(last_segment) = path.segments.last() {
self.visit_path_segment(last_segment);
}
}
_ => {
intravisit::walk_ty(self, ty);
}
}
}
fn visit_lifetime(&mut self, lifetime_ref: &'v hir::Lifetime) {
if let hir::LifetimeName::Param(def_id) = lifetime_ref.res {
self.regions.insert(def_id);
}
}
}
#[derive(Default)]
struct AllCollector {
regions: FxHashSet<LocalDefId>,
}
impl<'v> Visitor<'v> for AllCollector {
fn visit_lifetime(&mut self, lifetime_ref: &'v hir::Lifetime) {
if let hir::LifetimeName::Param(def_id) = lifetime_ref.res {
self.regions.insert(def_id);
}
}
}
}
pub fn deny_non_region_late_bound(
tcx: TyCtxt<'_>,
bound_vars: &mut FxIndexMap<LocalDefId, ResolvedArg>,
where_: &str,
) {
let mut first = true;
for (var, arg) in bound_vars {
let Node::GenericParam(param) = tcx.hir_node_by_def_id(*var) else {
span_bug!(tcx.def_span(*var), "expected bound-var def-id to resolve to param");
};
let what = match param.kind {
hir::GenericParamKind::Type { .. } => "type",
hir::GenericParamKind::Const { .. } => "const",
hir::GenericParamKind::Lifetime { .. } => continue,
};
let diag = tcx.dcx().struct_span_err(
param.span,
format!("late-bound {what} parameter not allowed on {where_}"),
);
let guar = if tcx.features().non_lifetime_binders && first {
diag.emit()
} else {
diag.delay_as_bug()
};
first = false;
*arg = ResolvedArg::Error(guar);
}
}