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(let_chains)]
68 #![feature(min_specialization)]
69 #![feature(never_type)]
70 #![feature(once_cell)]
71 #![feature(slice_partition_dedup)]
72 #![feature(try_blocks)]
73 #![feature(is_some_and)]
74 #![feature(type_alias_impl_trait)]
75 #![recursion_limit = "256"]
81 extern crate rustc_middle;
83 // These are used by Clippy.
90 // FIXME: This module shouldn't be public.
92 mod constrained_generic_params;
97 pub mod structured_errors;
100 use rustc_errors::{struct_span_err, ErrorGuaranteed};
101 use rustc_hir as hir;
102 use rustc_hir::def_id::DefId;
103 use rustc_hir::{Node, CRATE_HIR_ID};
104 use rustc_infer::infer::{InferOk, TyCtxtInferExt};
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::traits::error_reporting::TypeErrCtxtExt as _;
113 use rustc_trait_selection::traits::{self, ObligationCause, ObligationCauseCode};
117 use astconv::AstConv;
120 fn require_c_abi_if_c_variadic(tcx: TyCtxt<'_>, decl: &hir::FnDecl<'_>, abi: Abi, span: Span) {
121 match (decl.c_variadic, abi) {
122 // The function has the correct calling convention, or isn't a "C-variadic" function.
123 (false, _) | (true, Abi::C { .. }) | (true, Abi::Cdecl { .. }) => {}
124 // The function is a "C-variadic" function with an incorrect calling convention.
126 let mut err = struct_span_err!(
130 "C-variadic function must have C or cdecl calling convention"
132 err.span_label(span, "C-variadics require C or cdecl calling convention").emit();
137 fn require_same_types<'tcx>(
139 cause: &ObligationCause<'tcx>,
143 let infcx = &tcx.infer_ctxt().build();
144 let param_env = ty::ParamEnv::empty();
145 let errors = match infcx.at(cause, param_env).eq(expected, actual) {
146 Ok(InferOk { obligations, .. }) => traits::fully_solve_obligations(infcx, obligations),
148 infcx.err_ctxt().report_mismatched_types(cause, expected, actual, err).emit();
156 infcx.err_ctxt().report_fulfillment_errors(errors, None, false);
162 fn check_main_fn_ty(tcx: TyCtxt<'_>, main_def_id: DefId) {
163 let main_fnsig = tcx.fn_sig(main_def_id);
164 let main_span = tcx.def_span(main_def_id);
166 fn main_fn_diagnostics_hir_id(tcx: TyCtxt<'_>, def_id: DefId, sp: Span) -> hir::HirId {
167 if let Some(local_def_id) = def_id.as_local() {
168 let hir_id = tcx.hir().local_def_id_to_hir_id(local_def_id);
169 let hir_type = tcx.type_of(local_def_id);
170 if !matches!(hir_type.kind(), ty::FnDef(..)) {
171 span_bug!(sp, "main has a non-function type: found `{}`", hir_type);
179 fn main_fn_generics_params_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
180 if !def_id.is_local() {
183 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
184 match tcx.hir().find(hir_id) {
185 Some(Node::Item(hir::Item { kind: hir::ItemKind::Fn(_, ref generics, _), .. })) => {
186 if !generics.params.is_empty() {
193 span_bug!(tcx.def_span(def_id), "main has a non-function type");
198 fn main_fn_where_clauses_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
199 if !def_id.is_local() {
202 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
203 match tcx.hir().find(hir_id) {
204 Some(Node::Item(hir::Item { kind: hir::ItemKind::Fn(_, ref generics, _), .. })) => {
205 Some(generics.where_clause_span)
208 span_bug!(tcx.def_span(def_id), "main has a non-function type");
213 fn main_fn_asyncness_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
214 if !def_id.is_local() {
217 Some(tcx.def_span(def_id))
220 fn main_fn_return_type_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 { kind: hir::ItemKind::Fn(ref fn_sig, _, _), .. })) => {
227 Some(fn_sig.decl.output.span())
230 span_bug!(tcx.def_span(def_id), "main has a non-function type");
235 let mut error = false;
236 let main_diagnostics_hir_id = main_fn_diagnostics_hir_id(tcx, main_def_id, main_span);
237 let main_fn_generics = tcx.generics_of(main_def_id);
238 let main_fn_predicates = tcx.predicates_of(main_def_id);
239 if main_fn_generics.count() != 0 || !main_fnsig.bound_vars().is_empty() {
240 let generics_param_span = main_fn_generics_params_span(tcx, main_def_id);
241 let msg = "`main` function is not allowed to have generic \
244 struct_span_err!(tcx.sess, generics_param_span.unwrap_or(main_span), E0131, "{}", msg);
245 if let Some(generics_param_span) = generics_param_span {
246 let label = "`main` cannot have generic parameters";
247 diag.span_label(generics_param_span, label);
251 } else if !main_fn_predicates.predicates.is_empty() {
252 // generics may bring in implicit predicates, so we skip this check if generics is present.
253 let generics_where_clauses_span = main_fn_where_clauses_span(tcx, main_def_id);
254 let mut diag = struct_span_err!(
256 generics_where_clauses_span.unwrap_or(main_span),
258 "`main` function is not allowed to have a `where` clause"
260 if let Some(generics_where_clauses_span) = generics_where_clauses_span {
261 diag.span_label(generics_where_clauses_span, "`main` cannot have a `where` clause");
267 let main_asyncness = tcx.asyncness(main_def_id);
268 if let hir::IsAsync::Async = main_asyncness {
269 let mut diag = struct_span_err!(
273 "`main` function is not allowed to be `async`"
275 let asyncness_span = main_fn_asyncness_span(tcx, main_def_id);
276 if let Some(asyncness_span) = asyncness_span {
277 diag.span_label(asyncness_span, "`main` function is not allowed to be `async`");
283 for attr in tcx.get_attrs(main_def_id, sym::track_caller) {
285 .struct_span_err(attr.span, "`main` function is not allowed to be `#[track_caller]`")
286 .span_label(main_span, "`main` function is not allowed to be `#[track_caller]`")
295 let expected_return_type;
296 if let Some(term_did) = tcx.lang_items().termination() {
297 let return_ty = main_fnsig.output();
298 let return_ty_span = main_fn_return_type_span(tcx, main_def_id).unwrap_or(main_span);
299 if !return_ty.bound_vars().is_empty() {
300 let msg = "`main` function return type is not allowed to have generic \
302 struct_span_err!(tcx.sess, return_ty_span, E0131, "{}", msg).emit();
305 let return_ty = return_ty.skip_binder();
306 let infcx = tcx.infer_ctxt().build();
307 // Main should have no WC, so empty param env is OK here.
308 let param_env = ty::ParamEnv::empty();
309 let cause = traits::ObligationCause::new(
311 main_diagnostics_hir_id,
312 ObligationCauseCode::MainFunctionType,
314 let ocx = traits::ObligationCtxt::new(&infcx);
315 let norm_return_ty = ocx.normalize(cause.clone(), param_env, return_ty);
316 ocx.register_bound(cause, param_env, norm_return_ty, term_did);
317 let errors = ocx.select_all_or_error();
318 if !errors.is_empty() {
319 infcx.err_ctxt().report_fulfillment_errors(&errors, None, false);
322 // now we can take the return type of the given main function
323 expected_return_type = main_fnsig.output();
325 // standard () main return type
326 expected_return_type = ty::Binder::dummy(tcx.mk_unit());
333 let se_ty = tcx.mk_fn_ptr(expected_return_type.map_bound(|expected_return_type| {
334 tcx.mk_fn_sig(iter::empty(), expected_return_type, false, hir::Unsafety::Normal, Abi::Rust)
339 &ObligationCause::new(
341 main_diagnostics_hir_id,
342 ObligationCauseCode::MainFunctionType,
345 tcx.mk_fn_ptr(main_fnsig),
348 fn check_start_fn_ty(tcx: TyCtxt<'_>, start_def_id: DefId) {
349 let start_def_id = start_def_id.expect_local();
350 let start_id = tcx.hir().local_def_id_to_hir_id(start_def_id);
351 let start_span = tcx.def_span(start_def_id);
352 let start_t = tcx.type_of(start_def_id);
353 match start_t.kind() {
355 if let Some(Node::Item(it)) = tcx.hir().find(start_id) {
356 if let hir::ItemKind::Fn(ref sig, ref generics, _) = it.kind {
357 let mut error = false;
358 if !generics.params.is_empty() {
363 "start function is not allowed to have type parameters"
365 .span_label(generics.span, "start function cannot have type parameters")
369 if generics.has_where_clause_predicates {
372 generics.where_clause_span,
374 "start function is not allowed to have a `where` clause"
377 generics.where_clause_span,
378 "start function cannot have a `where` clause",
383 if let hir::IsAsync::Async = sig.header.asyncness {
384 let span = tcx.def_span(it.def_id);
389 "`start` is not allowed to be `async`"
391 .span_label(span, "`start` is not allowed to be `async`")
396 let attrs = tcx.hir().attrs(start_id);
398 if attr.has_name(sym::track_caller) {
402 "`start` is not allowed to be `#[track_caller]`",
406 "`start` is not allowed to be `#[track_caller]`",
419 let se_ty = tcx.mk_fn_ptr(ty::Binder::dummy(tcx.mk_fn_sig(
420 [tcx.types.isize, tcx.mk_imm_ptr(tcx.mk_imm_ptr(tcx.types.u8))].iter().cloned(),
423 hir::Unsafety::Normal,
429 &ObligationCause::new(start_span, start_id, ObligationCauseCode::StartFunctionType),
431 tcx.mk_fn_ptr(tcx.fn_sig(start_def_id)),
435 span_bug!(start_span, "start has a non-function type: found `{}`", start_t);
440 fn check_for_entry_fn(tcx: TyCtxt<'_>) {
441 match tcx.entry_fn(()) {
442 Some((def_id, EntryFnType::Main { .. })) => check_main_fn_ty(tcx, def_id),
443 Some((def_id, EntryFnType::Start)) => check_start_fn_ty(tcx, def_id),
448 pub fn provide(providers: &mut Providers) {
449 collect::provide(providers);
450 coherence::provide(providers);
451 check::provide(providers);
452 variance::provide(providers);
453 outlives::provide(providers);
454 impl_wf_check::provide(providers);
455 hir_wf_check::provide(providers);
458 pub fn check_crate(tcx: TyCtxt<'_>) -> Result<(), ErrorGuaranteed> {
459 let _prof_timer = tcx.sess.timer("type_check_crate");
461 // this ensures that later parts of type checking can assume that items
462 // have valid types and not error
463 // FIXME(matthewjasper) We shouldn't need to use `track_errors`.
464 tcx.sess.track_errors(|| {
465 tcx.sess.time("type_collecting", || {
466 tcx.hir().for_each_module(|module| tcx.ensure().collect_mod_item_types(module))
470 if tcx.features().rustc_attrs {
471 tcx.sess.track_errors(|| {
472 tcx.sess.time("outlives_testing", || outlives::test::test_inferred_outlives(tcx));
476 tcx.sess.track_errors(|| {
477 tcx.sess.time("impl_wf_inference", || {
478 tcx.hir().for_each_module(|module| tcx.ensure().check_mod_impl_wf(module))
482 tcx.sess.track_errors(|| {
483 tcx.sess.time("coherence_checking", || {
484 for &trait_def_id in tcx.all_local_trait_impls(()).keys() {
485 tcx.ensure().coherent_trait(trait_def_id);
488 // these queries are executed for side-effects (error reporting):
489 tcx.ensure().crate_inherent_impls(());
490 tcx.ensure().crate_inherent_impls_overlap_check(());
494 if tcx.features().rustc_attrs {
495 tcx.sess.track_errors(|| {
496 tcx.sess.time("variance_testing", || variance::test::test_variance(tcx));
500 tcx.sess.track_errors(|| {
501 tcx.sess.time("wf_checking", || {
502 tcx.hir().par_for_each_module(|module| tcx.ensure().check_mod_type_wf(module))
506 // NOTE: This is copy/pasted in librustdoc/core.rs and should be kept in sync.
507 tcx.sess.time("item_types_checking", || {
508 tcx.hir().for_each_module(|module| tcx.ensure().check_mod_item_types(module))
511 tcx.sess.time("item_bodies_checking", || tcx.typeck_item_bodies(()));
513 check_unused::check_crate(tcx);
514 check_for_entry_fn(tcx);
516 if let Some(reported) = tcx.sess.has_errors() { Err(reported) } else { Ok(()) }
519 /// A quasi-deprecated helper used in rustdoc and clippy to get
520 /// the type from a HIR node.
521 pub fn hir_ty_to_ty<'tcx>(tcx: TyCtxt<'tcx>, hir_ty: &hir::Ty<'_>) -> Ty<'tcx> {
522 // In case there are any projections, etc., find the "environment"
523 // def-ID that will be used to determine the traits/predicates in
524 // scope. This is derived from the enclosing item-like thing.
525 let env_def_id = tcx.hir().get_parent_item(hir_ty.hir_id);
526 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id.to_def_id());
527 <dyn AstConv<'_>>::ast_ty_to_ty(&item_cx, hir_ty)
530 pub fn hir_trait_to_predicates<'tcx>(
532 hir_trait: &hir::TraitRef<'_>,
535 // In case there are any projections, etc., find the "environment"
536 // def-ID that will be used to determine the traits/predicates in
537 // scope. This is derived from the enclosing item-like thing.
538 let env_def_id = tcx.hir().get_parent_item(hir_trait.hir_ref_id);
539 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id.to_def_id());
540 let mut bounds = Bounds::default();
541 let _ = <dyn AstConv<'_>>::instantiate_poly_trait_ref(
545 ty::BoundConstness::NotConst,