compiler/rustc_typeck/src/lib.rs

   1 /*!
   2
   3 # typeck
   4
   5 The type checker is responsible for:
   6
   7 1. Determining the type of each expression.
   8 2. Resolving methods and traits.
   9 3. Guaranteeing that most type rules are met. ("Most?", you say, "why most?"
  10    Well, dear reader, read on.)
  11
  12 The main entry point is [`check_crate()`]. Type checking operates in
  13 several major phases:
  14
  15 1. The collect phase first passes over all items and determines their
  16    type, without examining their "innards".
  17
  18 2. Variance inference then runs to compute the variance of each parameter.
  19
  20 3. Coherence checks for overlapping or orphaned impls.
  21
  22 4. Finally, the check phase then checks function bodies and so forth.
  23    Within the check phase, we check each function body one at a time
  24    (bodies of function expressions are checked as part of the
  25    containing function).  Inference is used to supply types wherever
  26    they are unknown. The actual checking of a function itself has
  27    several phases (check, regionck, writeback), as discussed in the
  28    documentation for the [`check`] module.
  29
  30 The type checker is defined into various submodules which are documented
  31 independently:
  32
  33 - astconv: converts the AST representation of types
  34   into the `ty` representation.
  35
  36 - collect: computes the types of each top-level item and enters them into
  37   the `tcx.types` table for later use.
  38
  39 - coherence: enforces coherence rules, builds some tables.
  40
  41 - variance: variance inference
  42
  43 - outlives: outlives inference
  44
  45 - check: walks over function bodies and type checks them, inferring types for
  46   local variables, type parameters, etc as necessary.
  47
  48 - infer: finds the types to use for each type variable such that
  49   all subtyping and assignment constraints are met.  In essence, the check
  50   module specifies the constraints, and the infer module solves them.
  51
  52 ## Note
  53
  54 This API is completely unstable and subject to change.
  55
  56 */
  57
  58 #![allow(rustc::potential_query_instability)]
  59 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
  60 #![feature(box_patterns)]
  61 #![feature(control_flow_enum)]
  62 #![feature(drain_filter)]
  63 #![feature(hash_drain_filter)]
  64 #![feature(if_let_guard)]
  65 #![feature(is_sorted)]
  66 #![feature(iter_intersperse)]
  67 #![feature(label_break_value)]
  68 #![feature(let_chains)]
  69 #![feature(let_else)]
  70 #![feature(min_specialization)]
  71 #![feature(never_type)]
  72 #![feature(once_cell)]
  73 #![feature(slice_partition_dedup)]
  74 #![feature(try_blocks)]
  75 #![recursion_limit = "256"]
  76
  77 #[macro_use]
  78 extern crate tracing;
  79
  80 #[macro_use]
  81 extern crate rustc_middle;
  82
  83 // These are used by Clippy.
  84 pub mod check;
  85 pub mod expr_use_visitor;
  86
  87 mod astconv;
  88 mod bounds;
  89 mod check_unused;
  90 mod coherence;
  91 mod collect;
  92 mod constrained_generic_params;
  93 mod errors;
  94 pub mod hir_wf_check;
  95 mod impl_wf_check;
  96 mod mem_categorization;
  97 mod outlives;
  98 mod structured_errors;
  99 mod variance;
 100
 101 use rustc_errors::{struct_span_err, ErrorGuaranteed};
 102 use rustc_hir as hir;
 103 use rustc_hir::def_id::DefId;
 104 use rustc_hir::{Node, CRATE_HIR_ID};
 105 use rustc_infer::infer::{InferOk, TyCtxtInferExt};
 106 use rustc_infer::traits::TraitEngineExt as _;
 107 use rustc_middle::middle;
 108 use rustc_middle::ty::query::Providers;
 109 use rustc_middle::ty::{self, Ty, TyCtxt};
 110 use rustc_middle::util;
 111 use rustc_session::config::EntryFnType;
 112 use rustc_span::{symbol::sym, Span, DUMMY_SP};
 113 use rustc_target::spec::abi::Abi;
 114 use rustc_trait_selection::infer::InferCtxtExt;
 115 use rustc_trait_selection::traits::error_reporting::InferCtxtExt as _;
 116 use rustc_trait_selection::traits::{
 117     self, ObligationCause, ObligationCauseCode, TraitEngine, TraitEngineExt as _,
 118 };
 119
 120 use std::iter;
 121
 122 use astconv::AstConv;
 123 use bounds::Bounds;
 124
 125 fn require_c_abi_if_c_variadic(tcx: TyCtxt<'_>, decl: &hir::FnDecl<'_>, abi: Abi, span: Span) {
 126     match (decl.c_variadic, abi) {
 127         // The function has the correct calling convention, or isn't a "C-variadic" function.
 128         (false, _) | (true, Abi::C { .. }) | (true, Abi::Cdecl { .. }) => {}
 129         // The function is a "C-variadic" function with an incorrect calling convention.
 130         (true, _) => {
 131             let mut err = struct_span_err!(
 132                 tcx.sess,
 133                 span,
 134                 E0045,
 135                 "C-variadic function must have C or cdecl calling convention"
 136             );
 137             err.span_label(span, "C-variadics require C or cdecl calling convention").emit();
 138         }
 139     }
 140 }
 141
 142 fn require_same_types<'tcx>(
 143     tcx: TyCtxt<'tcx>,
 144     cause: &ObligationCause<'tcx>,
 145     expected: Ty<'tcx>,
 146     actual: Ty<'tcx>,
 147 ) -> bool {
 148     tcx.infer_ctxt().enter(|ref infcx| {
 149         let param_env = ty::ParamEnv::empty();
 150         let mut fulfill_cx = <dyn TraitEngine<'_>>::new(infcx.tcx);
 151         match infcx.at(cause, param_env).eq(expected, actual) {
 152             Ok(InferOk { obligations, .. }) => {
 153                 fulfill_cx.register_predicate_obligations(infcx, obligations);
 154             }
 155             Err(err) => {
 156                 infcx.report_mismatched_types(cause, expected, actual, err).emit();
 157                 return false;
 158             }
 159         }
 160
 161         match fulfill_cx.select_all_or_error(infcx).as_slice() {
 162             [] => true,
 163             errors => {
 164                 infcx.report_fulfillment_errors(errors, None, false);
 165                 false
 166             }
 167         }
 168     })
 169 }
 170
 171 fn check_main_fn_ty(tcx: TyCtxt<'_>, main_def_id: DefId) {
 172     let main_fnsig = tcx.fn_sig(main_def_id);
 173     let main_span = tcx.def_span(main_def_id);
 174
 175     fn main_fn_diagnostics_hir_id(tcx: TyCtxt<'_>, def_id: DefId, sp: Span) -> hir::HirId {
 176         if let Some(local_def_id) = def_id.as_local() {
 177             let hir_id = tcx.hir().local_def_id_to_hir_id(local_def_id);
 178             let hir_type = tcx.type_of(local_def_id);
 179             if !matches!(hir_type.kind(), ty::FnDef(..)) {
 180                 span_bug!(sp, "main has a non-function type: found `{}`", hir_type);
 181             }
 182             hir_id
 183         } else {
 184             CRATE_HIR_ID
 185         }
 186     }
 187
 188     fn main_fn_generics_params_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
 189         if !def_id.is_local() {
 190             return None;
 191         }
 192         let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
 193         match tcx.hir().find(hir_id) {
 194             Some(Node::Item(hir::Item { kind: hir::ItemKind::Fn(_, ref generics, _), .. })) => {
 195                 if !generics.params.is_empty() {
 196                     Some(generics.span)
 197                 } else {
 198                     None
 199                 }
 200             }
 201             _ => {
 202                 span_bug!(tcx.def_span(def_id), "main has a non-function type");
 203             }
 204         }
 205     }
 206
 207     fn main_fn_where_clauses_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
 208         if !def_id.is_local() {
 209             return None;
 210         }
 211         let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
 212         match tcx.hir().find(hir_id) {
 213             Some(Node::Item(hir::Item { kind: hir::ItemKind::Fn(_, ref generics, _), .. })) => {
 214                 Some(generics.where_clause_span)
 215             }
 216             _ => {
 217                 span_bug!(tcx.def_span(def_id), "main has a non-function type");
 218             }
 219         }
 220     }
 221
 222     fn main_fn_asyncness_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
 223         if !def_id.is_local() {
 224             return None;
 225         }
 226         let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
 227         match tcx.hir().find(hir_id) {
 228             Some(Node::Item(hir::Item { span: item_span, .. })) => {
 229                 Some(tcx.sess.source_map().guess_head_span(*item_span))
 230             }
 231             _ => {
 232                 span_bug!(tcx.def_span(def_id), "main has a non-function type");
 233             }
 234         }
 235     }
 236
 237     fn main_fn_return_type_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
 238         if !def_id.is_local() {
 239             return None;
 240         }
 241         let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
 242         match tcx.hir().find(hir_id) {
 243             Some(Node::Item(hir::Item { kind: hir::ItemKind::Fn(ref fn_sig, _, _), .. })) => {
 244                 Some(fn_sig.decl.output.span())
 245             }
 246             _ => {
 247                 span_bug!(tcx.def_span(def_id), "main has a non-function type");
 248             }
 249         }
 250     }
 251
 252     let mut error = false;
 253     let main_diagnostics_hir_id = main_fn_diagnostics_hir_id(tcx, main_def_id, main_span);
 254     let main_fn_generics = tcx.generics_of(main_def_id);
 255     let main_fn_predicates = tcx.predicates_of(main_def_id);
 256     if main_fn_generics.count() != 0 || !main_fnsig.bound_vars().is_empty() {
 257         let generics_param_span = main_fn_generics_params_span(tcx, main_def_id);
 258         let msg = "`main` function is not allowed to have generic \
 259             parameters";
 260         let mut diag =
 261             struct_span_err!(tcx.sess, generics_param_span.unwrap_or(main_span), E0131, "{}", msg);
 262         if let Some(generics_param_span) = generics_param_span {
 263             let label = "`main` cannot have generic parameters".to_string();
 264             diag.span_label(generics_param_span, label);
 265         }
 266         diag.emit();
 267         error = true;
 268     } else if !main_fn_predicates.predicates.is_empty() {
 269         // generics may bring in implicit predicates, so we skip this check if generics is present.
 270         let generics_where_clauses_span = main_fn_where_clauses_span(tcx, main_def_id);
 271         let mut diag = struct_span_err!(
 272             tcx.sess,
 273             generics_where_clauses_span.unwrap_or(main_span),
 274             E0646,
 275             "`main` function is not allowed to have a `where` clause"
 276         );
 277         if let Some(generics_where_clauses_span) = generics_where_clauses_span {
 278             diag.span_label(generics_where_clauses_span, "`main` cannot have a `where` clause");
 279         }
 280         diag.emit();
 281         error = true;
 282     }
 283
 284     let main_asyncness = tcx.asyncness(main_def_id);
 285     if let hir::IsAsync::Async = main_asyncness {
 286         let mut diag = struct_span_err!(
 287             tcx.sess,
 288             main_span,
 289             E0752,
 290             "`main` function is not allowed to be `async`"
 291         );
 292         let asyncness_span = main_fn_asyncness_span(tcx, main_def_id);
 293         if let Some(asyncness_span) = asyncness_span {
 294             diag.span_label(asyncness_span, "`main` function is not allowed to be `async`");
 295         }
 296         diag.emit();
 297         error = true;
 298     }
 299
 300     for attr in tcx.get_attrs(main_def_id, sym::track_caller) {
 301         tcx.sess
 302             .struct_span_err(attr.span, "`main` function is not allowed to be `#[track_caller]`")
 303             .span_label(main_span, "`main` function is not allowed to be `#[track_caller]`")
 304             .emit();
 305         error = true;
 306     }
 307
 308     if error {
 309         return;
 310     }
 311
 312     let expected_return_type;
 313     if let Some(term_id) = tcx.lang_items().termination() {
 314         let return_ty = main_fnsig.output();
 315         let return_ty_span = main_fn_return_type_span(tcx, main_def_id).unwrap_or(main_span);
 316         if !return_ty.bound_vars().is_empty() {
 317             let msg = "`main` function return type is not allowed to have generic \
 318                     parameters"
 319                 .to_owned();
 320             struct_span_err!(tcx.sess, return_ty_span, E0131, "{}", msg).emit();
 321             error = true;
 322         }
 323         let return_ty = return_ty.skip_binder();
 324         tcx.infer_ctxt().enter(|infcx| {
 325             let cause = traits::ObligationCause::new(
 326                 return_ty_span,
 327                 main_diagnostics_hir_id,
 328                 ObligationCauseCode::MainFunctionType,
 329             );
 330             let mut fulfillment_cx = traits::FulfillmentContext::new();
 331             // normalize any potential projections in the return type, then add
 332             // any possible obligations to the fulfillment context.
 333             // HACK(ThePuzzlemaker) this feels symptomatic of a problem within
 334             // checking trait fulfillment, not this here. I'm not sure why it
 335             // works in the example in `fn test()` given in #88609? This also
 336             // probably isn't the best way to do this.
 337             let InferOk { value: norm_return_ty, obligations } = infcx
 338                 .partially_normalize_associated_types_in(
 339                     cause.clone(),
 340                     ty::ParamEnv::empty(),
 341                     return_ty,
 342                 );
 343             fulfillment_cx.register_predicate_obligations(&infcx, obligations);
 344             fulfillment_cx.register_bound(
 345                 &infcx,
 346                 ty::ParamEnv::empty(),
 347                 norm_return_ty,
 348                 term_id,
 349                 cause,
 350             );
 351             let errors = fulfillment_cx.select_all_or_error(&infcx);
 352             if !errors.is_empty() {
 353                 infcx.report_fulfillment_errors(&errors, None, false);
 354                 error = true;
 355             }
 356         });
 357         // now we can take the return type of the given main function
 358         expected_return_type = main_fnsig.output();
 359     } else {
 360         // standard () main return type
 361         expected_return_type = ty::Binder::dummy(tcx.mk_unit());
 362     }
 363
 364     if error {
 365         return;
 366     }
 367
 368     let se_ty = tcx.mk_fn_ptr(expected_return_type.map_bound(|expected_return_type| {
 369         tcx.mk_fn_sig(iter::empty(), expected_return_type, false, hir::Unsafety::Normal, Abi::Rust)
 370     }));
 371
 372     require_same_types(
 373         tcx,
 374         &ObligationCause::new(
 375             main_span,
 376             main_diagnostics_hir_id,
 377             ObligationCauseCode::MainFunctionType,
 378         ),
 379         se_ty,
 380         tcx.mk_fn_ptr(main_fnsig),
 381     );
 382 }
 383 fn check_start_fn_ty(tcx: TyCtxt<'_>, start_def_id: DefId) {
 384     let start_def_id = start_def_id.expect_local();
 385     let start_id = tcx.hir().local_def_id_to_hir_id(start_def_id);
 386     let start_span = tcx.def_span(start_def_id);
 387     let start_t = tcx.type_of(start_def_id);
 388     match start_t.kind() {
 389         ty::FnDef(..) => {
 390             if let Some(Node::Item(it)) = tcx.hir().find(start_id) {
 391                 if let hir::ItemKind::Fn(ref sig, ref generics, _) = it.kind {
 392                     let mut error = false;
 393                     if !generics.params.is_empty() {
 394                         struct_span_err!(
 395                             tcx.sess,
 396                             generics.span,
 397                             E0132,
 398                             "start function is not allowed to have type parameters"
 399                         )
 400                         .span_label(generics.span, "start function cannot have type parameters")
 401                         .emit();
 402                         error = true;
 403                     }
 404                     if generics.has_where_clause_predicates {
 405                         struct_span_err!(
 406                             tcx.sess,
 407                             generics.where_clause_span,
 408                             E0647,
 409                             "start function is not allowed to have a `where` clause"
 410                         )
 411                         .span_label(
 412                             generics.where_clause_span,
 413                             "start function cannot have a `where` clause",
 414                         )
 415                         .emit();
 416                         error = true;
 417                     }
 418                     if let hir::IsAsync::Async = sig.header.asyncness {
 419                         let span = tcx.sess.source_map().guess_head_span(it.span);
 420                         struct_span_err!(
 421                             tcx.sess,
 422                             span,
 423                             E0752,
 424                             "`start` is not allowed to be `async`"
 425                         )
 426                         .span_label(span, "`start` is not allowed to be `async`")
 427                         .emit();
 428                         error = true;
 429                     }
 430
 431                     let attrs = tcx.hir().attrs(start_id);
 432                     for attr in attrs {
 433                         if attr.has_name(sym::track_caller) {
 434                             tcx.sess
 435                                 .struct_span_err(
 436                                     attr.span,
 437                                     "`start` is not allowed to be `#[track_caller]`",
 438                                 )
 439                                 .span_label(
 440                                     start_span,
 441                                     "`start` is not allowed to be `#[track_caller]`",
 442                                 )
 443                                 .emit();
 444                             error = true;
 445                         }
 446                     }
 447
 448                     if error {
 449                         return;
 450                     }
 451                 }
 452             }
 453
 454             let se_ty = tcx.mk_fn_ptr(ty::Binder::dummy(tcx.mk_fn_sig(
 455                 [tcx.types.isize, tcx.mk_imm_ptr(tcx.mk_imm_ptr(tcx.types.u8))].iter().cloned(),
 456                 tcx.types.isize,
 457                 false,
 458                 hir::Unsafety::Normal,
 459                 Abi::Rust,
 460             )));
 461
 462             require_same_types(
 463                 tcx,
 464                 &ObligationCause::new(start_span, start_id, ObligationCauseCode::StartFunctionType),
 465                 se_ty,
 466                 tcx.mk_fn_ptr(tcx.fn_sig(start_def_id)),
 467             );
 468         }
 469         _ => {
 470             span_bug!(start_span, "start has a non-function type: found `{}`", start_t);
 471         }
 472     }
 473 }
 474
 475 fn check_for_entry_fn(tcx: TyCtxt<'_>) {
 476     match tcx.entry_fn(()) {
 477         Some((def_id, EntryFnType::Main)) => check_main_fn_ty(tcx, def_id),
 478         Some((def_id, EntryFnType::Start)) => check_start_fn_ty(tcx, def_id),
 479         _ => {}
 480     }
 481 }
 482
 483 pub fn provide(providers: &mut Providers) {
 484     collect::provide(providers);
 485     coherence::provide(providers);
 486     check::provide(providers);
 487     variance::provide(providers);
 488     outlives::provide(providers);
 489     impl_wf_check::provide(providers);
 490     hir_wf_check::provide(providers);
 491 }
 492
 493 pub fn check_crate(tcx: TyCtxt<'_>) -> Result<(), ErrorGuaranteed> {
 494     let _prof_timer = tcx.sess.timer("type_check_crate");
 495
 496     // this ensures that later parts of type checking can assume that items
 497     // have valid types and not error
 498     // FIXME(matthewjasper) We shouldn't need to use `track_errors`.
 499     tcx.sess.track_errors(|| {
 500         tcx.sess.time("type_collecting", || {
 501             tcx.hir().for_each_module(|module| tcx.ensure().collect_mod_item_types(module))
 502         });
 503     })?;
 504
 505     if tcx.features().rustc_attrs {
 506         tcx.sess.track_errors(|| {
 507             tcx.sess.time("outlives_testing", || outlives::test::test_inferred_outlives(tcx));
 508         })?;
 509     }
 510
 511     tcx.sess.track_errors(|| {
 512         tcx.sess.time("impl_wf_inference", || impl_wf_check::impl_wf_check(tcx));
 513     })?;
 514
 515     tcx.sess.track_errors(|| {
 516         tcx.sess.time("coherence_checking", || coherence::check_coherence(tcx));
 517     })?;
 518
 519     if tcx.features().rustc_attrs {
 520         tcx.sess.track_errors(|| {
 521             tcx.sess.time("variance_testing", || variance::test::test_variance(tcx));
 522         })?;
 523     }
 524
 525     tcx.sess.track_errors(|| {
 526         tcx.sess.time("wf_checking", || check::check_wf_new(tcx));
 527     })?;
 528
 529     // NOTE: This is copy/pasted in librustdoc/core.rs and should be kept in sync.
 530     tcx.sess.time("item_types_checking", || {
 531         tcx.hir().for_each_module(|module| tcx.ensure().check_mod_item_types(module))
 532     });
 533
 534     tcx.sess.time("item_bodies_checking", || tcx.typeck_item_bodies(()));
 535
 536     check_unused::check_crate(tcx);
 537     check_for_entry_fn(tcx);
 538
 539     if let Some(reported) = tcx.sess.has_errors() { Err(reported) } else { Ok(()) }
 540 }
 541
 542 /// A quasi-deprecated helper used in rustdoc and clippy to get
 543 /// the type from a HIR node.
 544 pub fn hir_ty_to_ty<'tcx>(tcx: TyCtxt<'tcx>, hir_ty: &hir::Ty<'_>) -> Ty<'tcx> {
 545     // In case there are any projections, etc., find the "environment"
 546     // def-ID that will be used to determine the traits/predicates in
 547     // scope.  This is derived from the enclosing item-like thing.
 548     let env_def_id = tcx.hir().get_parent_item(hir_ty.hir_id);
 549     let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id.to_def_id());
 550     <dyn AstConv<'_>>::ast_ty_to_ty(&item_cx, hir_ty)
 551 }
 552
 553 pub fn hir_trait_to_predicates<'tcx>(
 554     tcx: TyCtxt<'tcx>,
 555     hir_trait: &hir::TraitRef<'_>,
 556     self_ty: Ty<'tcx>,
 557 ) -> Bounds<'tcx> {
 558     // In case there are any projections, etc., find the "environment"
 559     // def-ID that will be used to determine the traits/predicates in
 560     // scope.  This is derived from the enclosing item-like thing.
 561     let env_def_id = tcx.hir().get_parent_item(hir_trait.hir_ref_id);
 562     let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id.to_def_id());
 563     let mut bounds = Bounds::default();
 564     let _ = <dyn AstConv<'_>>::instantiate_poly_trait_ref(
 565         &item_cx,
 566         hir_trait,
 567         DUMMY_SP,
 568         ty::BoundConstness::NotConst,
 569         self_ty,
 570         &mut bounds,
 571         true,
 572     );
 573
 574     bounds
 575 }