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::InferCtxtExt 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 tcx.infer_ctxt().enter(|ref infcx| {
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.report_mismatched_types(cause, expected, actual, err).emit();
157 infcx.report_fulfillment_errors(errors, None, false);
164 fn check_main_fn_ty(tcx: TyCtxt<'_>, main_def_id: DefId) {
165 let main_fnsig = tcx.fn_sig(main_def_id);
166 let main_span = tcx.def_span(main_def_id);
168 fn main_fn_diagnostics_hir_id(tcx: TyCtxt<'_>, def_id: DefId, sp: Span) -> hir::HirId {
169 if let Some(local_def_id) = def_id.as_local() {
170 let hir_id = tcx.hir().local_def_id_to_hir_id(local_def_id);
171 let hir_type = tcx.type_of(local_def_id);
172 if !matches!(hir_type.kind(), ty::FnDef(..)) {
173 span_bug!(sp, "main has a non-function type: found `{}`", hir_type);
181 fn main_fn_generics_params_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
182 if !def_id.is_local() {
185 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
186 match tcx.hir().find(hir_id) {
187 Some(Node::Item(hir::Item { kind: hir::ItemKind::Fn(_, ref generics, _), .. })) => {
188 if !generics.params.is_empty() {
195 span_bug!(tcx.def_span(def_id), "main has a non-function type");
200 fn main_fn_where_clauses_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
201 if !def_id.is_local() {
204 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
205 match tcx.hir().find(hir_id) {
206 Some(Node::Item(hir::Item { kind: hir::ItemKind::Fn(_, ref generics, _), .. })) => {
207 Some(generics.where_clause_span)
210 span_bug!(tcx.def_span(def_id), "main has a non-function type");
215 fn main_fn_asyncness_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
216 if !def_id.is_local() {
219 Some(tcx.def_span(def_id))
222 fn main_fn_return_type_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 { kind: hir::ItemKind::Fn(ref fn_sig, _, _), .. })) => {
229 Some(fn_sig.decl.output.span())
232 span_bug!(tcx.def_span(def_id), "main has a non-function type");
237 let mut error = false;
238 let main_diagnostics_hir_id = main_fn_diagnostics_hir_id(tcx, main_def_id, main_span);
239 let main_fn_generics = tcx.generics_of(main_def_id);
240 let main_fn_predicates = tcx.predicates_of(main_def_id);
241 if main_fn_generics.count() != 0 || !main_fnsig.bound_vars().is_empty() {
242 let generics_param_span = main_fn_generics_params_span(tcx, main_def_id);
243 let msg = "`main` function is not allowed to have generic \
246 struct_span_err!(tcx.sess, generics_param_span.unwrap_or(main_span), E0131, "{}", msg);
247 if let Some(generics_param_span) = generics_param_span {
248 let label = "`main` cannot have generic parameters";
249 diag.span_label(generics_param_span, label);
253 } else if !main_fn_predicates.predicates.is_empty() {
254 // generics may bring in implicit predicates, so we skip this check if generics is present.
255 let generics_where_clauses_span = main_fn_where_clauses_span(tcx, main_def_id);
256 let mut diag = struct_span_err!(
258 generics_where_clauses_span.unwrap_or(main_span),
260 "`main` function is not allowed to have a `where` clause"
262 if let Some(generics_where_clauses_span) = generics_where_clauses_span {
263 diag.span_label(generics_where_clauses_span, "`main` cannot have a `where` clause");
269 let main_asyncness = tcx.asyncness(main_def_id);
270 if let hir::IsAsync::Async = main_asyncness {
271 let mut diag = struct_span_err!(
275 "`main` function is not allowed to be `async`"
277 let asyncness_span = main_fn_asyncness_span(tcx, main_def_id);
278 if let Some(asyncness_span) = asyncness_span {
279 diag.span_label(asyncness_span, "`main` function is not allowed to be `async`");
285 for attr in tcx.get_attrs(main_def_id, sym::track_caller) {
287 .struct_span_err(attr.span, "`main` function is not allowed to be `#[track_caller]`")
288 .span_label(main_span, "`main` function is not allowed to be `#[track_caller]`")
297 let expected_return_type;
298 if let Some(term_did) = tcx.lang_items().termination() {
299 let return_ty = main_fnsig.output();
300 let return_ty_span = main_fn_return_type_span(tcx, main_def_id).unwrap_or(main_span);
301 if !return_ty.bound_vars().is_empty() {
302 let msg = "`main` function return type is not allowed to have generic \
304 struct_span_err!(tcx.sess, return_ty_span, E0131, "{}", msg).emit();
307 let return_ty = return_ty.skip_binder();
308 tcx.infer_ctxt().enter(|infcx| {
309 // Main should have no WC, so empty param env is OK here.
310 let param_env = ty::ParamEnv::empty();
311 let cause = traits::ObligationCause::new(
313 main_diagnostics_hir_id,
314 ObligationCauseCode::MainFunctionType,
316 let ocx = traits::ObligationCtxt::new(&infcx);
317 let norm_return_ty = ocx.normalize(cause.clone(), param_env, return_ty);
318 ocx.register_bound(cause, param_env, norm_return_ty, term_did);
319 let errors = ocx.select_all_or_error();
320 if !errors.is_empty() {
321 infcx.report_fulfillment_errors(&errors, None, false);
325 // now we can take the return type of the given main function
326 expected_return_type = main_fnsig.output();
328 // standard () main return type
329 expected_return_type = ty::Binder::dummy(tcx.mk_unit());
336 let se_ty = tcx.mk_fn_ptr(expected_return_type.map_bound(|expected_return_type| {
337 tcx.mk_fn_sig(iter::empty(), expected_return_type, false, hir::Unsafety::Normal, Abi::Rust)
342 &ObligationCause::new(
344 main_diagnostics_hir_id,
345 ObligationCauseCode::MainFunctionType,
348 tcx.mk_fn_ptr(main_fnsig),
351 fn check_start_fn_ty(tcx: TyCtxt<'_>, start_def_id: DefId) {
352 let start_def_id = start_def_id.expect_local();
353 let start_id = tcx.hir().local_def_id_to_hir_id(start_def_id);
354 let start_span = tcx.def_span(start_def_id);
355 let start_t = tcx.type_of(start_def_id);
356 match start_t.kind() {
358 if let Some(Node::Item(it)) = tcx.hir().find(start_id) {
359 if let hir::ItemKind::Fn(ref sig, ref generics, _) = it.kind {
360 let mut error = false;
361 if !generics.params.is_empty() {
366 "start function is not allowed to have type parameters"
368 .span_label(generics.span, "start function cannot have type parameters")
372 if generics.has_where_clause_predicates {
375 generics.where_clause_span,
377 "start function is not allowed to have a `where` clause"
380 generics.where_clause_span,
381 "start function cannot have a `where` clause",
386 if let hir::IsAsync::Async = sig.header.asyncness {
387 let span = tcx.def_span(it.def_id);
392 "`start` is not allowed to be `async`"
394 .span_label(span, "`start` is not allowed to be `async`")
399 let attrs = tcx.hir().attrs(start_id);
401 if attr.has_name(sym::track_caller) {
405 "`start` is not allowed to be `#[track_caller]`",
409 "`start` is not allowed to be `#[track_caller]`",
422 let se_ty = tcx.mk_fn_ptr(ty::Binder::dummy(tcx.mk_fn_sig(
423 [tcx.types.isize, tcx.mk_imm_ptr(tcx.mk_imm_ptr(tcx.types.u8))].iter().cloned(),
426 hir::Unsafety::Normal,
432 &ObligationCause::new(start_span, start_id, ObligationCauseCode::StartFunctionType),
434 tcx.mk_fn_ptr(tcx.fn_sig(start_def_id)),
438 span_bug!(start_span, "start has a non-function type: found `{}`", start_t);
443 fn check_for_entry_fn(tcx: TyCtxt<'_>) {
444 match tcx.entry_fn(()) {
445 Some((def_id, EntryFnType::Main { .. })) => check_main_fn_ty(tcx, def_id),
446 Some((def_id, EntryFnType::Start)) => check_start_fn_ty(tcx, def_id),
451 pub fn provide(providers: &mut Providers) {
452 collect::provide(providers);
453 coherence::provide(providers);
454 check::provide(providers);
455 variance::provide(providers);
456 outlives::provide(providers);
457 impl_wf_check::provide(providers);
458 hir_wf_check::provide(providers);
461 pub fn check_crate(tcx: TyCtxt<'_>) -> Result<(), ErrorGuaranteed> {
462 let _prof_timer = tcx.sess.timer("type_check_crate");
464 // this ensures that later parts of type checking can assume that items
465 // have valid types and not error
466 // FIXME(matthewjasper) We shouldn't need to use `track_errors`.
467 tcx.sess.track_errors(|| {
468 tcx.sess.time("type_collecting", || {
469 tcx.hir().for_each_module(|module| tcx.ensure().collect_mod_item_types(module))
473 if tcx.features().rustc_attrs {
474 tcx.sess.track_errors(|| {
475 tcx.sess.time("outlives_testing", || outlives::test::test_inferred_outlives(tcx));
479 tcx.sess.track_errors(|| {
480 tcx.sess.time("impl_wf_inference", || {
481 tcx.hir().for_each_module(|module| tcx.ensure().check_mod_impl_wf(module))
485 tcx.sess.track_errors(|| {
486 tcx.sess.time("coherence_checking", || {
487 for &trait_def_id in tcx.all_local_trait_impls(()).keys() {
488 tcx.ensure().coherent_trait(trait_def_id);
491 // these queries are executed for side-effects (error reporting):
492 tcx.ensure().crate_inherent_impls(());
493 tcx.ensure().crate_inherent_impls_overlap_check(());
497 if tcx.features().rustc_attrs {
498 tcx.sess.track_errors(|| {
499 tcx.sess.time("variance_testing", || variance::test::test_variance(tcx));
503 tcx.sess.track_errors(|| {
504 tcx.sess.time("wf_checking", || {
505 tcx.hir().par_for_each_module(|module| tcx.ensure().check_mod_type_wf(module))
509 // NOTE: This is copy/pasted in librustdoc/core.rs and should be kept in sync.
510 tcx.sess.time("item_types_checking", || {
511 tcx.hir().for_each_module(|module| tcx.ensure().check_mod_item_types(module))
514 tcx.sess.time("item_bodies_checking", || tcx.typeck_item_bodies(()));
516 check_unused::check_crate(tcx);
517 check_for_entry_fn(tcx);
519 if let Some(reported) = tcx.sess.has_errors() { Err(reported) } else { Ok(()) }
522 /// A quasi-deprecated helper used in rustdoc and clippy to get
523 /// the type from a HIR node.
524 pub fn hir_ty_to_ty<'tcx>(tcx: TyCtxt<'tcx>, hir_ty: &hir::Ty<'_>) -> Ty<'tcx> {
525 // In case there are any projections, etc., find the "environment"
526 // def-ID that will be used to determine the traits/predicates in
527 // scope. This is derived from the enclosing item-like thing.
528 let env_def_id = tcx.hir().get_parent_item(hir_ty.hir_id);
529 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id.to_def_id());
530 <dyn AstConv<'_>>::ast_ty_to_ty(&item_cx, hir_ty)
533 pub fn hir_trait_to_predicates<'tcx>(
535 hir_trait: &hir::TraitRef<'_>,
538 // In case there are any projections, etc., find the "environment"
539 // def-ID that will be used to determine the traits/predicates in
540 // scope. This is derived from the enclosing item-like thing.
541 let env_def_id = tcx.hir().get_parent_item(hir_trait.hir_ref_id);
542 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id.to_def_id());
543 let mut bounds = Bounds::default();
544 let _ = <dyn AstConv<'_>>::instantiate_poly_trait_ref(
548 ty::BoundConstness::NotConst,