5 The type checker is responsible for:
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.)
12 The main entry point is [`check_crate()`]. Type checking operates in
15 1. The collect phase first passes over all items and determines their
16 type, without examining their "innards".
18 2. Variance inference then runs to compute the variance of each parameter.
20 3. Coherence checks for overlapping or orphaned impls.
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.
30 The type checker is defined into various submodules which are documented
33 - astconv: converts the AST representation of types
34 into the `ty` representation.
36 - collect: computes the types of each top-level item and enters them into
37 the `tcx.types` table for later use.
39 - coherence: enforces coherence rules, builds some tables.
41 - variance: variance inference
43 - outlives: outlives inference
45 - check: walks over function bodies and type checks them, inferring types for
46 local variables, type parameters, etc as necessary.
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.
54 This API is completely unstable and subject to change.
58 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
59 #![feature(bool_to_option)]
60 #![feature(crate_visibility_modifier)]
61 #![feature(if_let_guard)]
62 #![feature(is_sorted)]
64 #![feature(min_specialization)]
66 #![feature(try_blocks)]
67 #![feature(never_type)]
68 #![feature(slice_partition_dedup)]
69 #![feature(control_flow_enum)]
70 #![feature(hash_drain_filter)]
71 #![feature(once_cell)]
72 #![recursion_limit = "256"]
73 #![cfg_attr(not(bootstrap), allow(rustc::potential_query_instability))]
79 extern crate rustc_middle;
81 // These are used by Clippy.
83 pub mod expr_use_visitor;
90 mod constrained_generic_params;
94 mod mem_categorization;
96 mod structured_errors;
99 use rustc_errors::{struct_span_err, ErrorReported};
100 use rustc_hir as hir;
101 use rustc_hir::def_id::DefId;
102 use rustc_hir::{Node, CRATE_HIR_ID};
103 use rustc_infer::infer::{InferOk, TyCtxtInferExt};
104 use rustc_infer::traits::TraitEngineExt as _;
105 use rustc_middle::middle;
106 use rustc_middle::ty::query::Providers;
107 use rustc_middle::ty::{self, Ty, TyCtxt};
108 use rustc_middle::util;
109 use rustc_session::config::EntryFnType;
110 use rustc_span::{symbol::sym, Span, DUMMY_SP};
111 use rustc_target::spec::abi::Abi;
112 use rustc_trait_selection::infer::InferCtxtExt;
113 use rustc_trait_selection::traits::error_reporting::InferCtxtExt as _;
114 use rustc_trait_selection::traits::{
115 self, ObligationCause, ObligationCauseCode, TraitEngine, TraitEngineExt as _,
120 use astconv::AstConv;
123 fn require_c_abi_if_c_variadic(tcx: TyCtxt<'_>, decl: &hir::FnDecl<'_>, abi: Abi, span: Span) {
124 match (decl.c_variadic, abi) {
125 // The function has the correct calling convention, or isn't a "C-variadic" function.
126 (false, _) | (true, Abi::C { .. }) | (true, Abi::Cdecl { .. }) => {}
127 // The function is a "C-variadic" function with an incorrect calling convention.
129 let mut err = struct_span_err!(
133 "C-variadic function must have C or cdecl calling convention"
135 err.span_label(span, "C-variadics require C or cdecl calling convention").emit();
140 fn require_same_types<'tcx>(
142 cause: &ObligationCause<'tcx>,
146 tcx.infer_ctxt().enter(|ref infcx| {
147 let param_env = ty::ParamEnv::empty();
148 let mut fulfill_cx = <dyn TraitEngine<'_>>::new(infcx.tcx);
149 match infcx.at(cause, param_env).eq(expected, actual) {
150 Ok(InferOk { obligations, .. }) => {
151 fulfill_cx.register_predicate_obligations(infcx, obligations);
154 infcx.report_mismatched_types(cause, expected, actual, err).emit();
159 match fulfill_cx.select_all_or_error(infcx).as_slice() {
162 infcx.report_fulfillment_errors(errors, None, false);
169 fn check_main_fn_ty(tcx: TyCtxt<'_>, main_def_id: DefId) {
170 let main_fnsig = tcx.fn_sig(main_def_id);
171 let main_span = tcx.def_span(main_def_id);
173 fn main_fn_diagnostics_hir_id(tcx: TyCtxt<'_>, def_id: DefId, sp: Span) -> hir::HirId {
174 if let Some(local_def_id) = def_id.as_local() {
175 let hir_id = tcx.hir().local_def_id_to_hir_id(local_def_id);
176 let hir_type = tcx.type_of(local_def_id);
177 if !matches!(hir_type.kind(), ty::FnDef(..)) {
178 span_bug!(sp, "main has a non-function type: found `{}`", hir_type);
186 fn main_fn_generics_params_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
187 if !def_id.is_local() {
190 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
191 match tcx.hir().find(hir_id) {
192 Some(Node::Item(hir::Item { kind: hir::ItemKind::Fn(_, ref generics, _), .. })) => {
193 if !generics.params.is_empty() {
200 span_bug!(tcx.def_span(def_id), "main has a non-function type");
205 fn main_fn_where_clauses_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
206 if !def_id.is_local() {
209 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
210 match tcx.hir().find(hir_id) {
211 Some(Node::Item(hir::Item { kind: hir::ItemKind::Fn(_, ref generics, _), .. })) => {
212 generics.where_clause.span()
215 span_bug!(tcx.def_span(def_id), "main has a non-function type");
220 fn main_fn_asyncness_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
221 if !def_id.is_local() {
224 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
225 match tcx.hir().find(hir_id) {
226 Some(Node::Item(hir::Item { span: item_span, .. })) => {
227 Some(tcx.sess.source_map().guess_head_span(*item_span))
230 span_bug!(tcx.def_span(def_id), "main has a non-function type");
235 fn main_fn_return_type_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
236 if !def_id.is_local() {
239 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
240 match tcx.hir().find(hir_id) {
241 Some(Node::Item(hir::Item { kind: hir::ItemKind::Fn(ref fn_sig, _, _), .. })) => {
242 Some(fn_sig.decl.output.span())
245 span_bug!(tcx.def_span(def_id), "main has a non-function type");
250 let mut error = false;
251 let main_diagnostics_hir_id = main_fn_diagnostics_hir_id(tcx, main_def_id, main_span);
252 let main_fn_generics = tcx.generics_of(main_def_id);
253 let main_fn_predicates = tcx.predicates_of(main_def_id);
254 if main_fn_generics.count() != 0 || !main_fnsig.bound_vars().is_empty() {
255 let generics_param_span = main_fn_generics_params_span(tcx, main_def_id);
256 let msg = "`main` function is not allowed to have generic \
259 struct_span_err!(tcx.sess, generics_param_span.unwrap_or(main_span), E0131, "{}", msg);
260 if let Some(generics_param_span) = generics_param_span {
261 let label = "`main` cannot have generic parameters".to_string();
262 diag.span_label(generics_param_span, label);
266 } else if !main_fn_predicates.predicates.is_empty() {
267 // generics may bring in implicit predicates, so we skip this check if generics is present.
268 let generics_where_clauses_span = main_fn_where_clauses_span(tcx, main_def_id);
269 let mut diag = struct_span_err!(
271 generics_where_clauses_span.unwrap_or(main_span),
273 "`main` function is not allowed to have a `where` clause"
275 if let Some(generics_where_clauses_span) = generics_where_clauses_span {
276 diag.span_label(generics_where_clauses_span, "`main` cannot have a `where` clause");
282 let main_asyncness = tcx.asyncness(main_def_id);
283 if let hir::IsAsync::Async = main_asyncness {
284 let mut diag = struct_span_err!(
288 "`main` function is not allowed to be `async`"
290 let asyncness_span = main_fn_asyncness_span(tcx, main_def_id);
291 if let Some(asyncness_span) = asyncness_span {
292 diag.span_label(asyncness_span, "`main` function is not allowed to be `async`");
298 for attr in tcx.get_attrs(main_def_id) {
299 if attr.has_name(sym::track_caller) {
303 "`main` function is not allowed to be `#[track_caller]`",
305 .span_label(main_span, "`main` function is not allowed to be `#[track_caller]`")
315 let expected_return_type;
316 if let Some(term_id) = tcx.lang_items().termination() {
317 let return_ty = main_fnsig.output();
318 let return_ty_span = main_fn_return_type_span(tcx, main_def_id).unwrap_or(main_span);
319 if !return_ty.bound_vars().is_empty() {
320 let msg = "`main` function return type is not allowed to have generic \
323 struct_span_err!(tcx.sess, return_ty_span, E0131, "{}", msg).emit();
326 let return_ty = return_ty.skip_binder();
327 tcx.infer_ctxt().enter(|infcx| {
328 let cause = traits::ObligationCause::new(
330 main_diagnostics_hir_id,
331 ObligationCauseCode::MainFunctionType,
333 let mut fulfillment_cx = traits::FulfillmentContext::new();
334 // normalize any potential projections in the return type, then add
335 // any possible obligations to the fulfillment context.
336 // HACK(ThePuzzlemaker) this feels symptomatic of a problem within
337 // checking trait fulfillment, not this here. I'm not sure why it
338 // works in the example in `fn test()` given in #88609? This also
339 // probably isn't the best way to do this.
340 let InferOk { value: norm_return_ty, obligations } = infcx
341 .partially_normalize_associated_types_in(
343 ty::ParamEnv::empty(),
346 fulfillment_cx.register_predicate_obligations(&infcx, obligations);
347 fulfillment_cx.register_bound(
349 ty::ParamEnv::empty(),
354 let errors = fulfillment_cx.select_all_or_error(&infcx);
355 if !errors.is_empty() {
356 infcx.report_fulfillment_errors(&errors, None, false);
360 // now we can take the return type of the given main function
361 expected_return_type = main_fnsig.output();
363 // standard () main return type
364 expected_return_type = ty::Binder::dummy(tcx.mk_unit());
371 let se_ty = tcx.mk_fn_ptr(expected_return_type.map_bound(|expected_return_type| {
372 tcx.mk_fn_sig(iter::empty(), expected_return_type, false, hir::Unsafety::Normal, Abi::Rust)
377 &ObligationCause::new(
379 main_diagnostics_hir_id,
380 ObligationCauseCode::MainFunctionType,
383 tcx.mk_fn_ptr(main_fnsig),
386 fn check_start_fn_ty(tcx: TyCtxt<'_>, start_def_id: DefId) {
387 let start_def_id = start_def_id.expect_local();
388 let start_id = tcx.hir().local_def_id_to_hir_id(start_def_id);
389 let start_span = tcx.def_span(start_def_id);
390 let start_t = tcx.type_of(start_def_id);
391 match start_t.kind() {
393 if let Some(Node::Item(it)) = tcx.hir().find(start_id) {
394 if let hir::ItemKind::Fn(ref sig, ref generics, _) = it.kind {
395 let mut error = false;
396 if !generics.params.is_empty() {
401 "start function is not allowed to have type parameters"
403 .span_label(generics.span, "start function cannot have type parameters")
407 if let Some(sp) = generics.where_clause.span() {
412 "start function is not allowed to have a `where` clause"
414 .span_label(sp, "start function cannot have a `where` clause")
418 if let hir::IsAsync::Async = sig.header.asyncness {
419 let span = tcx.sess.source_map().guess_head_span(it.span);
424 "`start` is not allowed to be `async`"
426 .span_label(span, "`start` is not allowed to be `async`")
431 let attrs = tcx.hir().attrs(start_id);
433 if attr.has_name(sym::track_caller) {
437 "`start` is not allowed to be `#[track_caller]`",
441 "`start` is not allowed to be `#[track_caller]`",
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(),
458 hir::Unsafety::Normal,
464 &ObligationCause::new(start_span, start_id, ObligationCauseCode::StartFunctionType),
466 tcx.mk_fn_ptr(tcx.fn_sig(start_def_id)),
470 span_bug!(start_span, "start has a non-function type: found `{}`", start_t);
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),
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);
493 pub fn check_crate(tcx: TyCtxt<'_>) -> Result<(), ErrorReported> {
494 let _prof_timer = tcx.sess.timer("type_check_crate");
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))
505 if tcx.features().rustc_attrs {
506 tcx.sess.track_errors(|| {
507 tcx.sess.time("outlives_testing", || outlives::test::test_inferred_outlives(tcx));
511 tcx.sess.track_errors(|| {
512 tcx.sess.time("impl_wf_inference", || impl_wf_check::impl_wf_check(tcx));
515 tcx.sess.track_errors(|| {
516 tcx.sess.time("coherence_checking", || coherence::check_coherence(tcx));
519 if tcx.features().rustc_attrs {
520 tcx.sess.track_errors(|| {
521 tcx.sess.time("variance_testing", || variance::test::test_variance(tcx));
525 tcx.sess.track_errors(|| {
526 tcx.sess.time("wf_checking", || check::check_wf_new(tcx));
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))
534 tcx.sess.time("item_bodies_checking", || tcx.typeck_item_bodies(()));
536 check_unused::check_crate(tcx);
537 check_for_entry_fn(tcx);
539 if tcx.sess.err_count() == 0 { Ok(()) } else { Err(ErrorReported) }
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)
553 pub fn hir_trait_to_predicates<'tcx>(
555 hir_trait: &hir::TraitRef<'_>,
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(
568 ty::BoundConstness::NotConst,