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 #![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)]
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"]
81 extern crate rustc_middle;
83 // These are used by Clippy.
85 pub mod expr_use_visitor;
92 mod constrained_generic_params;
96 mod mem_categorization;
98 mod structured_errors;
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 _,
122 use astconv::AstConv;
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.
131 let mut err = struct_span_err!(
135 "C-variadic function must have C or cdecl calling convention"
137 err.span_label(span, "C-variadics require C or cdecl calling convention").emit();
142 fn require_same_types<'tcx>(
144 cause: &ObligationCause<'tcx>,
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);
156 infcx.report_mismatched_types(cause, expected, actual, err).emit();
161 match fulfill_cx.select_all_or_error(infcx).as_slice() {
164 infcx.report_fulfillment_errors(errors, None, false);
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);
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);
188 fn main_fn_generics_params_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
189 if !def_id.is_local() {
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() {
202 span_bug!(tcx.def_span(def_id), "main has a non-function type");
207 fn main_fn_where_clauses_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
208 if !def_id.is_local() {
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)
217 span_bug!(tcx.def_span(def_id), "main has a non-function type");
222 fn main_fn_asyncness_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
223 if !def_id.is_local() {
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))
232 span_bug!(tcx.def_span(def_id), "main has a non-function type");
237 fn main_fn_return_type_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
238 if !def_id.is_local() {
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())
247 span_bug!(tcx.def_span(def_id), "main has a non-function type");
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 \
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);
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!(
273 generics_where_clauses_span.unwrap_or(main_span),
275 "`main` function is not allowed to have a `where` clause"
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");
284 let main_asyncness = tcx.asyncness(main_def_id);
285 if let hir::IsAsync::Async = main_asyncness {
286 let mut diag = struct_span_err!(
290 "`main` function is not allowed to be `async`"
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`");
300 for attr in tcx.get_attrs(main_def_id, sym::track_caller) {
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]`")
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 \
320 struct_span_err!(tcx.sess, return_ty_span, E0131, "{}", msg).emit();
323 let return_ty = return_ty.skip_binder();
324 tcx.infer_ctxt().enter(|infcx| {
325 let cause = traits::ObligationCause::new(
327 main_diagnostics_hir_id,
328 ObligationCauseCode::MainFunctionType,
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(
340 ty::ParamEnv::empty(),
343 fulfillment_cx.register_predicate_obligations(&infcx, obligations);
344 fulfillment_cx.register_bound(
346 ty::ParamEnv::empty(),
351 let errors = fulfillment_cx.select_all_or_error(&infcx);
352 if !errors.is_empty() {
353 infcx.report_fulfillment_errors(&errors, None, false);
357 // now we can take the return type of the given main function
358 expected_return_type = main_fnsig.output();
360 // standard () main return type
361 expected_return_type = ty::Binder::dummy(tcx.mk_unit());
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)
374 &ObligationCause::new(
376 main_diagnostics_hir_id,
377 ObligationCauseCode::MainFunctionType,
380 tcx.mk_fn_ptr(main_fnsig),
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() {
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() {
398 "start function is not allowed to have type parameters"
400 .span_label(generics.span, "start function cannot have type parameters")
404 if generics.has_where_clause_predicates {
407 generics.where_clause_span,
409 "start function is not allowed to have a `where` clause"
412 generics.where_clause_span,
413 "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<(), ErrorGuaranteed> {
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 let Some(reported) = tcx.sess.has_errors() { Err(reported) } else { Ok(()) }
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,