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(bool_to_option)]
61 #![feature(box_patterns)]
62 #![feature(control_flow_enum)]
63 #![feature(crate_visibility_modifier)]
64 #![feature(drain_filter)]
65 #![feature(hash_drain_filter)]
66 #![feature(if_let_guard)]
67 #![feature(is_sorted)]
68 #![feature(label_break_value)]
69 #![feature(let_chains)]
71 #![feature(min_specialization)]
72 #![feature(never_type)]
74 #![feature(once_cell)]
75 #![feature(slice_partition_dedup)]
76 #![feature(try_blocks)]
77 #![recursion_limit = "256"]
83 extern crate rustc_middle;
85 // These are used by Clippy.
87 pub mod expr_use_visitor;
94 mod constrained_generic_params;
98 mod mem_categorization;
100 mod structured_errors;
103 use rustc_errors::{struct_span_err, ErrorGuaranteed};
104 use rustc_hir as hir;
105 use rustc_hir::def_id::DefId;
106 use rustc_hir::{Node, CRATE_HIR_ID};
107 use rustc_infer::infer::{InferOk, TyCtxtInferExt};
108 use rustc_infer::traits::TraitEngineExt as _;
109 use rustc_middle::middle;
110 use rustc_middle::ty::query::Providers;
111 use rustc_middle::ty::{self, Ty, TyCtxt};
112 use rustc_middle::util;
113 use rustc_session::config::EntryFnType;
114 use rustc_span::{symbol::sym, Span, DUMMY_SP};
115 use rustc_target::spec::abi::Abi;
116 use rustc_trait_selection::infer::InferCtxtExt;
117 use rustc_trait_selection::traits::error_reporting::InferCtxtExt as _;
118 use rustc_trait_selection::traits::{
119 self, ObligationCause, ObligationCauseCode, TraitEngine, TraitEngineExt as _,
124 use astconv::AstConv;
127 fn require_c_abi_if_c_variadic(tcx: TyCtxt<'_>, decl: &hir::FnDecl<'_>, abi: Abi, span: Span) {
128 match (decl.c_variadic, abi) {
129 // The function has the correct calling convention, or isn't a "C-variadic" function.
130 (false, _) | (true, Abi::C { .. }) | (true, Abi::Cdecl { .. }) => {}
131 // The function is a "C-variadic" function with an incorrect calling convention.
133 let mut err = struct_span_err!(
137 "C-variadic function must have C or cdecl calling convention"
139 err.span_label(span, "C-variadics require C or cdecl calling convention").emit();
144 fn require_same_types<'tcx>(
146 cause: &ObligationCause<'tcx>,
150 tcx.infer_ctxt().enter(|ref infcx| {
151 let param_env = ty::ParamEnv::empty();
152 let mut fulfill_cx = <dyn TraitEngine<'_>>::new(infcx.tcx);
153 match infcx.at(cause, param_env).eq(expected, actual) {
154 Ok(InferOk { obligations, .. }) => {
155 fulfill_cx.register_predicate_obligations(infcx, obligations);
158 infcx.report_mismatched_types(cause, expected, actual, err).emit();
163 match fulfill_cx.select_all_or_error(infcx).as_slice() {
166 infcx.report_fulfillment_errors(errors, None, false);
173 fn check_main_fn_ty(tcx: TyCtxt<'_>, main_def_id: DefId) {
174 let main_fnsig = tcx.fn_sig(main_def_id);
175 let main_span = tcx.def_span(main_def_id);
177 fn main_fn_diagnostics_hir_id(tcx: TyCtxt<'_>, def_id: DefId, sp: Span) -> hir::HirId {
178 if let Some(local_def_id) = def_id.as_local() {
179 let hir_id = tcx.hir().local_def_id_to_hir_id(local_def_id);
180 let hir_type = tcx.type_of(local_def_id);
181 if !matches!(hir_type.kind(), ty::FnDef(..)) {
182 span_bug!(sp, "main has a non-function type: found `{}`", hir_type);
190 fn main_fn_generics_params_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
191 if !def_id.is_local() {
194 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
195 match tcx.hir().find(hir_id) {
196 Some(Node::Item(hir::Item { kind: hir::ItemKind::Fn(_, ref generics, _), .. })) => {
197 if !generics.params.is_empty() {
204 span_bug!(tcx.def_span(def_id), "main has a non-function type");
209 fn main_fn_where_clauses_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
210 if !def_id.is_local() {
213 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
214 match tcx.hir().find(hir_id) {
215 Some(Node::Item(hir::Item { kind: hir::ItemKind::Fn(_, ref generics, _), .. })) => {
216 generics.where_clause.span()
219 span_bug!(tcx.def_span(def_id), "main has a non-function type");
224 fn main_fn_asyncness_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
225 if !def_id.is_local() {
228 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
229 match tcx.hir().find(hir_id) {
230 Some(Node::Item(hir::Item { span: item_span, .. })) => {
231 Some(tcx.sess.source_map().guess_head_span(*item_span))
234 span_bug!(tcx.def_span(def_id), "main has a non-function type");
239 fn main_fn_return_type_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
240 if !def_id.is_local() {
243 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
244 match tcx.hir().find(hir_id) {
245 Some(Node::Item(hir::Item { kind: hir::ItemKind::Fn(ref fn_sig, _, _), .. })) => {
246 Some(fn_sig.decl.output.span())
249 span_bug!(tcx.def_span(def_id), "main has a non-function type");
254 let mut error = false;
255 let main_diagnostics_hir_id = main_fn_diagnostics_hir_id(tcx, main_def_id, main_span);
256 let main_fn_generics = tcx.generics_of(main_def_id);
257 let main_fn_predicates = tcx.predicates_of(main_def_id);
258 if main_fn_generics.count() != 0 || !main_fnsig.bound_vars().is_empty() {
259 let generics_param_span = main_fn_generics_params_span(tcx, main_def_id);
260 let msg = "`main` function is not allowed to have generic \
263 struct_span_err!(tcx.sess, generics_param_span.unwrap_or(main_span), E0131, "{}", msg);
264 if let Some(generics_param_span) = generics_param_span {
265 let label = "`main` cannot have generic parameters".to_string();
266 diag.span_label(generics_param_span, label);
270 } else if !main_fn_predicates.predicates.is_empty() {
271 // generics may bring in implicit predicates, so we skip this check if generics is present.
272 let generics_where_clauses_span = main_fn_where_clauses_span(tcx, main_def_id);
273 let mut diag = struct_span_err!(
275 generics_where_clauses_span.unwrap_or(main_span),
277 "`main` function is not allowed to have a `where` clause"
279 if let Some(generics_where_clauses_span) = generics_where_clauses_span {
280 diag.span_label(generics_where_clauses_span, "`main` cannot have a `where` clause");
286 let main_asyncness = tcx.asyncness(main_def_id);
287 if let hir::IsAsync::Async = main_asyncness {
288 let mut diag = struct_span_err!(
292 "`main` function is not allowed to be `async`"
294 let asyncness_span = main_fn_asyncness_span(tcx, main_def_id);
295 if let Some(asyncness_span) = asyncness_span {
296 diag.span_label(asyncness_span, "`main` function is not allowed to be `async`");
302 for attr in tcx.get_attrs(main_def_id) {
303 if attr.has_name(sym::track_caller) {
307 "`main` function is not allowed to be `#[track_caller]`",
309 .span_label(main_span, "`main` function is not allowed to be `#[track_caller]`")
319 let expected_return_type;
320 if let Some(term_id) = tcx.lang_items().termination() {
321 let return_ty = main_fnsig.output();
322 let return_ty_span = main_fn_return_type_span(tcx, main_def_id).unwrap_or(main_span);
323 if !return_ty.bound_vars().is_empty() {
324 let msg = "`main` function return type is not allowed to have generic \
327 struct_span_err!(tcx.sess, return_ty_span, E0131, "{}", msg).emit();
330 let return_ty = return_ty.skip_binder();
331 tcx.infer_ctxt().enter(|infcx| {
332 let cause = traits::ObligationCause::new(
334 main_diagnostics_hir_id,
335 ObligationCauseCode::MainFunctionType,
337 let mut fulfillment_cx = traits::FulfillmentContext::new();
338 // normalize any potential projections in the return type, then add
339 // any possible obligations to the fulfillment context.
340 // HACK(ThePuzzlemaker) this feels symptomatic of a problem within
341 // checking trait fulfillment, not this here. I'm not sure why it
342 // works in the example in `fn test()` given in #88609? This also
343 // probably isn't the best way to do this.
344 let InferOk { value: norm_return_ty, obligations } = infcx
345 .partially_normalize_associated_types_in(
347 ty::ParamEnv::empty(),
350 fulfillment_cx.register_predicate_obligations(&infcx, obligations);
351 fulfillment_cx.register_bound(
353 ty::ParamEnv::empty(),
358 let errors = fulfillment_cx.select_all_or_error(&infcx);
359 if !errors.is_empty() {
360 infcx.report_fulfillment_errors(&errors, None, false);
364 // now we can take the return type of the given main function
365 expected_return_type = main_fnsig.output();
367 // standard () main return type
368 expected_return_type = ty::Binder::dummy(tcx.mk_unit());
375 let se_ty = tcx.mk_fn_ptr(expected_return_type.map_bound(|expected_return_type| {
376 tcx.mk_fn_sig(iter::empty(), expected_return_type, false, hir::Unsafety::Normal, Abi::Rust)
381 &ObligationCause::new(
383 main_diagnostics_hir_id,
384 ObligationCauseCode::MainFunctionType,
387 tcx.mk_fn_ptr(main_fnsig),
390 fn check_start_fn_ty(tcx: TyCtxt<'_>, start_def_id: DefId) {
391 let start_def_id = start_def_id.expect_local();
392 let start_id = tcx.hir().local_def_id_to_hir_id(start_def_id);
393 let start_span = tcx.def_span(start_def_id);
394 let start_t = tcx.type_of(start_def_id);
395 match start_t.kind() {
397 if let Some(Node::Item(it)) = tcx.hir().find(start_id) {
398 if let hir::ItemKind::Fn(ref sig, ref generics, _) = it.kind {
399 let mut error = false;
400 if !generics.params.is_empty() {
405 "start function is not allowed to have type parameters"
407 .span_label(generics.span, "start function cannot have type parameters")
411 if let Some(sp) = generics.where_clause.span() {
416 "start function is not allowed to have a `where` clause"
418 .span_label(sp, "start function cannot have a `where` clause")
422 if let hir::IsAsync::Async = sig.header.asyncness {
423 let span = tcx.sess.source_map().guess_head_span(it.span);
428 "`start` is not allowed to be `async`"
430 .span_label(span, "`start` is not allowed to be `async`")
435 let attrs = tcx.hir().attrs(start_id);
437 if attr.has_name(sym::track_caller) {
441 "`start` is not allowed to be `#[track_caller]`",
445 "`start` is not allowed to be `#[track_caller]`",
458 let se_ty = tcx.mk_fn_ptr(ty::Binder::dummy(tcx.mk_fn_sig(
459 [tcx.types.isize, tcx.mk_imm_ptr(tcx.mk_imm_ptr(tcx.types.u8))].iter().cloned(),
462 hir::Unsafety::Normal,
468 &ObligationCause::new(start_span, start_id, ObligationCauseCode::StartFunctionType),
470 tcx.mk_fn_ptr(tcx.fn_sig(start_def_id)),
474 span_bug!(start_span, "start has a non-function type: found `{}`", start_t);
479 fn check_for_entry_fn(tcx: TyCtxt<'_>) {
480 match tcx.entry_fn(()) {
481 Some((def_id, EntryFnType::Main)) => check_main_fn_ty(tcx, def_id),
482 Some((def_id, EntryFnType::Start)) => check_start_fn_ty(tcx, def_id),
487 pub fn provide(providers: &mut Providers) {
488 collect::provide(providers);
489 coherence::provide(providers);
490 check::provide(providers);
491 variance::provide(providers);
492 outlives::provide(providers);
493 impl_wf_check::provide(providers);
494 hir_wf_check::provide(providers);
497 pub fn check_crate(tcx: TyCtxt<'_>) -> Result<(), ErrorGuaranteed> {
498 let _prof_timer = tcx.sess.timer("type_check_crate");
500 // this ensures that later parts of type checking can assume that items
501 // have valid types and not error
502 // FIXME(matthewjasper) We shouldn't need to use `track_errors`.
503 tcx.sess.track_errors(|| {
504 tcx.sess.time("type_collecting", || {
505 tcx.hir().for_each_module(|module| tcx.ensure().collect_mod_item_types(module))
509 if tcx.features().rustc_attrs {
510 tcx.sess.track_errors(|| {
511 tcx.sess.time("outlives_testing", || outlives::test::test_inferred_outlives(tcx));
515 tcx.sess.track_errors(|| {
516 tcx.sess.time("impl_wf_inference", || impl_wf_check::impl_wf_check(tcx));
519 tcx.sess.track_errors(|| {
520 tcx.sess.time("coherence_checking", || coherence::check_coherence(tcx));
523 if tcx.features().rustc_attrs {
524 tcx.sess.track_errors(|| {
525 tcx.sess.time("variance_testing", || variance::test::test_variance(tcx));
529 tcx.sess.track_errors(|| {
530 tcx.sess.time("wf_checking", || check::check_wf_new(tcx));
533 // NOTE: This is copy/pasted in librustdoc/core.rs and should be kept in sync.
534 tcx.sess.time("item_types_checking", || {
535 tcx.hir().for_each_module(|module| tcx.ensure().check_mod_item_types(module))
538 tcx.sess.time("item_bodies_checking", || tcx.typeck_item_bodies(()));
540 check_unused::check_crate(tcx);
541 check_for_entry_fn(tcx);
543 if let Some(reported) = tcx.sess.has_errors() { Err(reported) } else { Ok(()) }
546 /// A quasi-deprecated helper used in rustdoc and clippy to get
547 /// the type from a HIR node.
548 pub fn hir_ty_to_ty<'tcx>(tcx: TyCtxt<'tcx>, hir_ty: &hir::Ty<'_>) -> Ty<'tcx> {
549 // In case there are any projections, etc., find the "environment"
550 // def-ID that will be used to determine the traits/predicates in
551 // scope. This is derived from the enclosing item-like thing.
552 let env_def_id = tcx.hir().get_parent_item(hir_ty.hir_id);
553 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id.to_def_id());
554 <dyn AstConv<'_>>::ast_ty_to_ty(&item_cx, hir_ty)
557 pub fn hir_trait_to_predicates<'tcx>(
559 hir_trait: &hir::TraitRef<'_>,
562 // In case there are any projections, etc., find the "environment"
563 // def-ID that will be used to determine the traits/predicates in
564 // scope. This is derived from the enclosing item-like thing.
565 let env_def_id = tcx.hir().get_parent_item(hir_trait.hir_ref_id);
566 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id.to_def_id());
567 let mut bounds = Bounds::default();
568 let _ = <dyn AstConv<'_>>::instantiate_poly_trait_ref(
572 ty::BoundConstness::NotConst,