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.
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_middle::middle;
107 use rustc_middle::ty::query::Providers;
108 use rustc_middle::ty::{self, Ty, TyCtxt};
109 use rustc_middle::util;
110 use rustc_session::config::EntryFnType;
111 use rustc_span::{symbol::sym, Span, DUMMY_SP};
112 use rustc_target::spec::abi::Abi;
113 use rustc_trait_selection::traits::error_reporting::TypeErrCtxtExt as _;
114 use rustc_trait_selection::traits::{self, ObligationCause, ObligationCauseCode};
118 use astconv::AstConv;
121 fn require_c_abi_if_c_variadic(tcx: TyCtxt<'_>, decl: &hir::FnDecl<'_>, abi: Abi, span: Span) {
122 match (decl.c_variadic, abi) {
123 // The function has the correct calling convention, or isn't a "C-variadic" function.
124 (false, _) | (true, Abi::C { .. }) | (true, Abi::Cdecl { .. }) => {}
125 // The function is a "C-variadic" function with an incorrect calling convention.
127 let mut err = struct_span_err!(
131 "C-variadic function must have C or cdecl calling convention"
133 err.span_label(span, "C-variadics require C or cdecl calling convention").emit();
138 fn require_same_types<'tcx>(
140 cause: &ObligationCause<'tcx>,
144 let infcx = &tcx.infer_ctxt().build();
145 let param_env = ty::ParamEnv::empty();
146 let errors = match infcx.at(cause, param_env).eq(expected, actual) {
147 Ok(InferOk { obligations, .. }) => traits::fully_solve_obligations(infcx, obligations),
149 infcx.err_ctxt().report_mismatched_types(cause, expected, actual, err).emit();
157 infcx.err_ctxt().report_fulfillment_errors(errors, None, false);
163 fn check_main_fn_ty(tcx: TyCtxt<'_>, main_def_id: DefId) {
164 let main_fnsig = tcx.fn_sig(main_def_id);
165 let main_span = tcx.def_span(main_def_id);
167 fn main_fn_diagnostics_hir_id(tcx: TyCtxt<'_>, def_id: DefId, sp: Span) -> hir::HirId {
168 if let Some(local_def_id) = def_id.as_local() {
169 let hir_id = tcx.hir().local_def_id_to_hir_id(local_def_id);
170 let hir_type = tcx.type_of(local_def_id);
171 if !matches!(hir_type.kind(), ty::FnDef(..)) {
172 span_bug!(sp, "main has a non-function type: found `{}`", hir_type);
180 fn main_fn_generics_params_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
181 if !def_id.is_local() {
184 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
185 match tcx.hir().find(hir_id) {
186 Some(Node::Item(hir::Item { kind: hir::ItemKind::Fn(_, ref generics, _), .. })) => {
187 if !generics.params.is_empty() {
194 span_bug!(tcx.def_span(def_id), "main has a non-function type");
199 fn main_fn_where_clauses_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
200 if !def_id.is_local() {
203 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
204 match tcx.hir().find(hir_id) {
205 Some(Node::Item(hir::Item { kind: hir::ItemKind::Fn(_, ref generics, _), .. })) => {
206 Some(generics.where_clause_span)
209 span_bug!(tcx.def_span(def_id), "main has a non-function type");
214 fn main_fn_asyncness_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
215 if !def_id.is_local() {
218 Some(tcx.def_span(def_id))
221 fn main_fn_return_type_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
222 if !def_id.is_local() {
225 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
226 match tcx.hir().find(hir_id) {
227 Some(Node::Item(hir::Item { kind: hir::ItemKind::Fn(ref fn_sig, _, _), .. })) => {
228 Some(fn_sig.decl.output.span())
231 span_bug!(tcx.def_span(def_id), "main has a non-function type");
236 let mut error = false;
237 let main_diagnostics_hir_id = main_fn_diagnostics_hir_id(tcx, main_def_id, main_span);
238 let main_fn_generics = tcx.generics_of(main_def_id);
239 let main_fn_predicates = tcx.predicates_of(main_def_id);
240 if main_fn_generics.count() != 0 || !main_fnsig.bound_vars().is_empty() {
241 let generics_param_span = main_fn_generics_params_span(tcx, main_def_id);
242 let msg = "`main` function is not allowed to have generic \
245 struct_span_err!(tcx.sess, generics_param_span.unwrap_or(main_span), E0131, "{}", msg);
246 if let Some(generics_param_span) = generics_param_span {
247 let label = "`main` cannot have generic parameters";
248 diag.span_label(generics_param_span, label);
252 } else if !main_fn_predicates.predicates.is_empty() {
253 // generics may bring in implicit predicates, so we skip this check if generics is present.
254 let generics_where_clauses_span = main_fn_where_clauses_span(tcx, main_def_id);
255 let mut diag = struct_span_err!(
257 generics_where_clauses_span.unwrap_or(main_span),
259 "`main` function is not allowed to have a `where` clause"
261 if let Some(generics_where_clauses_span) = generics_where_clauses_span {
262 diag.span_label(generics_where_clauses_span, "`main` cannot have a `where` clause");
268 let main_asyncness = tcx.asyncness(main_def_id);
269 if let hir::IsAsync::Async = main_asyncness {
270 let mut diag = struct_span_err!(
274 "`main` function is not allowed to be `async`"
276 let asyncness_span = main_fn_asyncness_span(tcx, main_def_id);
277 if let Some(asyncness_span) = asyncness_span {
278 diag.span_label(asyncness_span, "`main` function is not allowed to be `async`");
284 for attr in tcx.get_attrs(main_def_id, sym::track_caller) {
286 .struct_span_err(attr.span, "`main` function is not allowed to be `#[track_caller]`")
287 .span_label(main_span, "`main` function is not allowed to be `#[track_caller]`")
296 let expected_return_type;
297 if let Some(term_did) = tcx.lang_items().termination() {
298 let return_ty = main_fnsig.output();
299 let return_ty_span = main_fn_return_type_span(tcx, main_def_id).unwrap_or(main_span);
300 if !return_ty.bound_vars().is_empty() {
301 let msg = "`main` function return type is not allowed to have generic \
303 struct_span_err!(tcx.sess, return_ty_span, E0131, "{}", msg).emit();
306 let return_ty = return_ty.skip_binder();
307 let infcx = tcx.infer_ctxt().build();
308 // Main should have no WC, so empty param env is OK here.
309 let param_env = ty::ParamEnv::empty();
310 let cause = traits::ObligationCause::new(
312 main_diagnostics_hir_id,
313 ObligationCauseCode::MainFunctionType,
315 let ocx = traits::ObligationCtxt::new(&infcx);
316 let norm_return_ty = ocx.normalize(cause.clone(), param_env, return_ty);
317 ocx.register_bound(cause, param_env, norm_return_ty, term_did);
318 let errors = ocx.select_all_or_error();
319 if !errors.is_empty() {
320 infcx.err_ctxt().report_fulfillment_errors(&errors, None, false);
323 // now we can take the return type of the given main function
324 expected_return_type = main_fnsig.output();
326 // standard () main return type
327 expected_return_type = ty::Binder::dummy(tcx.mk_unit());
334 let se_ty = tcx.mk_fn_ptr(expected_return_type.map_bound(|expected_return_type| {
335 tcx.mk_fn_sig(iter::empty(), expected_return_type, false, hir::Unsafety::Normal, Abi::Rust)
340 &ObligationCause::new(
342 main_diagnostics_hir_id,
343 ObligationCauseCode::MainFunctionType,
346 tcx.mk_fn_ptr(main_fnsig),
349 fn check_start_fn_ty(tcx: TyCtxt<'_>, start_def_id: DefId) {
350 let start_def_id = start_def_id.expect_local();
351 let start_id = tcx.hir().local_def_id_to_hir_id(start_def_id);
352 let start_span = tcx.def_span(start_def_id);
353 let start_t = tcx.type_of(start_def_id);
354 match start_t.kind() {
356 if let Some(Node::Item(it)) = tcx.hir().find(start_id) {
357 if let hir::ItemKind::Fn(ref sig, ref generics, _) = it.kind {
358 let mut error = false;
359 if !generics.params.is_empty() {
364 "start function is not allowed to have type parameters"
366 .span_label(generics.span, "start function cannot have type parameters")
370 if generics.has_where_clause_predicates {
373 generics.where_clause_span,
375 "start function is not allowed to have a `where` clause"
378 generics.where_clause_span,
379 "start function cannot have a `where` clause",
384 if let hir::IsAsync::Async = sig.header.asyncness {
385 let span = tcx.def_span(it.def_id);
390 "`start` is not allowed to be `async`"
392 .span_label(span, "`start` is not allowed to be `async`")
397 let attrs = tcx.hir().attrs(start_id);
399 if attr.has_name(sym::track_caller) {
403 "`start` is not allowed to be `#[track_caller]`",
407 "`start` is not allowed to be `#[track_caller]`",
420 let se_ty = tcx.mk_fn_ptr(ty::Binder::dummy(tcx.mk_fn_sig(
421 [tcx.types.isize, tcx.mk_imm_ptr(tcx.mk_imm_ptr(tcx.types.u8))].iter().cloned(),
424 hir::Unsafety::Normal,
430 &ObligationCause::new(start_span, start_id, ObligationCauseCode::StartFunctionType),
432 tcx.mk_fn_ptr(tcx.fn_sig(start_def_id)),
436 span_bug!(start_span, "start has a non-function type: found `{}`", start_t);
441 fn check_for_entry_fn(tcx: TyCtxt<'_>) {
442 match tcx.entry_fn(()) {
443 Some((def_id, EntryFnType::Main { .. })) => check_main_fn_ty(tcx, def_id),
444 Some((def_id, EntryFnType::Start)) => check_start_fn_ty(tcx, def_id),
449 pub fn provide(providers: &mut Providers) {
450 collect::provide(providers);
451 coherence::provide(providers);
452 check::provide(providers);
453 variance::provide(providers);
454 outlives::provide(providers);
455 impl_wf_check::provide(providers);
456 hir_wf_check::provide(providers);
459 pub fn check_crate(tcx: TyCtxt<'_>) -> Result<(), ErrorGuaranteed> {
460 let _prof_timer = tcx.sess.timer("type_check_crate");
462 // this ensures that later parts of type checking can assume that items
463 // have valid types and not error
464 // FIXME(matthewjasper) We shouldn't need to use `track_errors`.
465 tcx.sess.track_errors(|| {
466 tcx.sess.time("type_collecting", || {
467 tcx.hir().for_each_module(|module| tcx.ensure().collect_mod_item_types(module))
471 if tcx.features().rustc_attrs {
472 tcx.sess.track_errors(|| {
473 tcx.sess.time("outlives_testing", || outlives::test::test_inferred_outlives(tcx));
477 tcx.sess.track_errors(|| {
478 tcx.sess.time("impl_wf_inference", || {
479 tcx.hir().for_each_module(|module| tcx.ensure().check_mod_impl_wf(module))
483 tcx.sess.track_errors(|| {
484 tcx.sess.time("coherence_checking", || {
485 for &trait_def_id in tcx.all_local_trait_impls(()).keys() {
486 tcx.ensure().coherent_trait(trait_def_id);
489 // these queries are executed for side-effects (error reporting):
490 tcx.ensure().crate_inherent_impls(());
491 tcx.ensure().crate_inherent_impls_overlap_check(());
495 if tcx.features().rustc_attrs {
496 tcx.sess.track_errors(|| {
497 tcx.sess.time("variance_testing", || variance::test::test_variance(tcx));
501 tcx.sess.track_errors(|| {
502 tcx.sess.time("wf_checking", || {
503 tcx.hir().par_for_each_module(|module| tcx.ensure().check_mod_type_wf(module))
507 // NOTE: This is copy/pasted in librustdoc/core.rs and should be kept in sync.
508 tcx.sess.time("item_types_checking", || {
509 tcx.hir().for_each_module(|module| tcx.ensure().check_mod_item_types(module))
512 tcx.sess.time("item_bodies_checking", || tcx.typeck_item_bodies(()));
514 check_unused::check_crate(tcx);
515 check_for_entry_fn(tcx);
517 if let Some(reported) = tcx.sess.has_errors() { Err(reported) } else { Ok(()) }
520 /// A quasi-deprecated helper used in rustdoc and clippy to get
521 /// the type from a HIR node.
522 pub fn hir_ty_to_ty<'tcx>(tcx: TyCtxt<'tcx>, hir_ty: &hir::Ty<'_>) -> Ty<'tcx> {
523 // In case there are any projections, etc., find the "environment"
524 // def-ID that will be used to determine the traits/predicates in
525 // scope. This is derived from the enclosing item-like thing.
526 let env_def_id = tcx.hir().get_parent_item(hir_ty.hir_id);
527 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id.to_def_id());
528 <dyn AstConv<'_>>::ast_ty_to_ty(&item_cx, hir_ty)
531 pub fn hir_trait_to_predicates<'tcx>(
533 hir_trait: &hir::TraitRef<'_>,
536 // In case there are any projections, etc., find the "environment"
537 // def-ID that will be used to determine the traits/predicates in
538 // scope. This is derived from the enclosing item-like thing.
539 let env_def_id = tcx.hir().get_parent_item(hir_trait.hir_ref_id);
540 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id.to_def_id());
541 let mut bounds = Bounds::default();
542 let _ = <dyn AstConv<'_>>::instantiate_poly_trait_ref(
546 ty::BoundConstness::NotConst,