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.
91 // FIXME: This module shouldn't be public.
93 mod constrained_generic_params;
98 pub mod structured_errors;
101 use rustc_errors::{struct_span_err, ErrorGuaranteed};
102 use rustc_hir as hir;
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, parse::feature_err};
110 use rustc_span::def_id::{DefId, LocalDefId, CRATE_DEF_ID};
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};
119 use astconv::AstConv;
122 fn require_c_abi_if_c_variadic(tcx: TyCtxt<'_>, decl: &hir::FnDecl<'_>, abi: Abi, span: Span) {
123 const ERROR_HEAD: &str = "C-variadic function must have a compatible calling convention";
124 const CONVENTIONS_UNSTABLE: &str = "`C`, `cdecl`, `win64`, `sysv64` or `efiapi`";
125 const CONVENTIONS_STABLE: &str = "`C` or `cdecl`";
126 const UNSTABLE_EXPLAIN: &str =
127 "using calling conventions other than `C` or `cdecl` for varargs functions is unstable";
129 if !decl.c_variadic || matches!(abi, Abi::C { .. } | Abi::Cdecl { .. }) {
133 let extended_abi_support = tcx.features().extended_varargs_abi_support;
134 let conventions = match (extended_abi_support, abi.supports_varargs()) {
135 // User enabled additional ABI support for varargs and function ABI matches those ones.
136 (true, true) => return,
138 // Using this ABI would be ok, if the feature for additional ABI support was enabled.
139 // Return CONVENTIONS_STABLE, because we want the other error to look the same.
142 &tcx.sess.parse_sess,
143 sym::extended_varargs_abi_support,
151 (false, false) => CONVENTIONS_STABLE,
152 (true, false) => CONVENTIONS_UNSTABLE,
155 let mut err = struct_span_err!(tcx.sess, span, E0045, "{}, like {}", ERROR_HEAD, conventions);
156 err.span_label(span, ERROR_HEAD).emit();
159 fn require_same_types<'tcx>(
161 cause: &ObligationCause<'tcx>,
165 let infcx = &tcx.infer_ctxt().build();
166 let param_env = ty::ParamEnv::empty();
167 let errors = match infcx.at(cause, param_env).eq(expected, actual) {
168 Ok(InferOk { obligations, .. }) => traits::fully_solve_obligations(infcx, obligations),
170 infcx.err_ctxt().report_mismatched_types(cause, expected, actual, err).emit();
178 infcx.err_ctxt().report_fulfillment_errors(errors, None);
184 fn check_main_fn_ty(tcx: TyCtxt<'_>, main_def_id: DefId) {
185 let main_fnsig = tcx.fn_sig(main_def_id);
186 let main_span = tcx.def_span(main_def_id);
188 fn main_fn_diagnostics_def_id(tcx: TyCtxt<'_>, def_id: DefId, sp: Span) -> LocalDefId {
189 if let Some(local_def_id) = def_id.as_local() {
190 let hir_type = tcx.type_of(local_def_id);
191 if !matches!(hir_type.kind(), ty::FnDef(..)) {
192 span_bug!(sp, "main has a non-function type: found `{}`", hir_type);
200 fn main_fn_generics_params_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(_, generics, _), .. })) => {
207 generics.params.is_empty().not().then(|| generics.span)
210 span_bug!(tcx.def_span(def_id), "main has a non-function type");
215 fn main_fn_where_clauses_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
216 if !def_id.is_local() {
219 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
220 match tcx.hir().find(hir_id) {
221 Some(Node::Item(hir::Item { kind: hir::ItemKind::Fn(_, generics, _), .. })) => {
222 Some(generics.where_clause_span)
225 span_bug!(tcx.def_span(def_id), "main has a non-function type");
230 fn main_fn_asyncness_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
231 if !def_id.is_local() {
234 Some(tcx.def_span(def_id))
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(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_def_id = main_fn_diagnostics_def_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";
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_did) = 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 \
319 struct_span_err!(tcx.sess, return_ty_span, E0131, "{}", msg).emit();
322 let return_ty = return_ty.skip_binder();
323 let infcx = tcx.infer_ctxt().build();
324 // Main should have no WC, so empty param env is OK here.
325 let param_env = ty::ParamEnv::empty();
326 let cause = traits::ObligationCause::new(
328 main_diagnostics_def_id,
329 ObligationCauseCode::MainFunctionType,
331 let ocx = traits::ObligationCtxt::new(&infcx);
332 let norm_return_ty = ocx.normalize(&cause, param_env, return_ty);
333 ocx.register_bound(cause, param_env, norm_return_ty, term_did);
334 let errors = ocx.select_all_or_error();
335 if !errors.is_empty() {
336 infcx.err_ctxt().report_fulfillment_errors(&errors, None);
339 // now we can take the return type of the given main function
340 expected_return_type = main_fnsig.output();
342 // standard () main return type
343 expected_return_type = ty::Binder::dummy(tcx.mk_unit());
350 let se_ty = tcx.mk_fn_ptr(expected_return_type.map_bound(|expected_return_type| {
351 tcx.mk_fn_sig(iter::empty(), expected_return_type, false, hir::Unsafety::Normal, Abi::Rust)
356 &ObligationCause::new(
358 main_diagnostics_def_id,
359 ObligationCauseCode::MainFunctionType,
362 tcx.mk_fn_ptr(main_fnsig),
365 fn check_start_fn_ty(tcx: TyCtxt<'_>, start_def_id: DefId) {
366 let start_def_id = start_def_id.expect_local();
367 let start_id = tcx.hir().local_def_id_to_hir_id(start_def_id);
368 let start_span = tcx.def_span(start_def_id);
369 let start_t = tcx.type_of(start_def_id);
370 match start_t.kind() {
372 if let Some(Node::Item(it)) = tcx.hir().find(start_id) {
373 if let hir::ItemKind::Fn(sig, generics, _) = &it.kind {
374 let mut error = false;
375 if !generics.params.is_empty() {
380 "start function is not allowed to have type parameters"
382 .span_label(generics.span, "start function cannot have type parameters")
386 if generics.has_where_clause_predicates {
389 generics.where_clause_span,
391 "start function is not allowed to have a `where` clause"
394 generics.where_clause_span,
395 "start function cannot have a `where` clause",
400 if let hir::IsAsync::Async = sig.header.asyncness {
401 let span = tcx.def_span(it.owner_id);
406 "`start` is not allowed to be `async`"
408 .span_label(span, "`start` is not allowed to be `async`")
413 let attrs = tcx.hir().attrs(start_id);
415 if attr.has_name(sym::track_caller) {
419 "`start` is not allowed to be `#[track_caller]`",
423 "`start` is not allowed to be `#[track_caller]`",
436 let se_ty = tcx.mk_fn_ptr(ty::Binder::dummy(tcx.mk_fn_sig(
437 [tcx.types.isize, tcx.mk_imm_ptr(tcx.mk_imm_ptr(tcx.types.u8))].iter().cloned(),
440 hir::Unsafety::Normal,
446 &ObligationCause::new(
449 ObligationCauseCode::StartFunctionType,
452 tcx.mk_fn_ptr(tcx.fn_sig(start_def_id)),
456 span_bug!(start_span, "start has a non-function type: found `{}`", start_t);
461 fn check_for_entry_fn(tcx: TyCtxt<'_>) {
462 match tcx.entry_fn(()) {
463 Some((def_id, EntryFnType::Main { .. })) => check_main_fn_ty(tcx, def_id),
464 Some((def_id, EntryFnType::Start)) => check_start_fn_ty(tcx, def_id),
469 pub fn provide(providers: &mut Providers) {
470 collect::provide(providers);
471 coherence::provide(providers);
472 check::provide(providers);
473 variance::provide(providers);
474 outlives::provide(providers);
475 impl_wf_check::provide(providers);
476 hir_wf_check::provide(providers);
479 pub fn check_crate(tcx: TyCtxt<'_>) -> Result<(), ErrorGuaranteed> {
480 let _prof_timer = tcx.sess.timer("type_check_crate");
482 // this ensures that later parts of type checking can assume that items
483 // have valid types and not error
484 // FIXME(matthewjasper) We shouldn't need to use `track_errors`.
485 tcx.sess.track_errors(|| {
486 tcx.sess.time("type_collecting", || {
487 tcx.hir().for_each_module(|module| tcx.ensure().collect_mod_item_types(module))
491 if tcx.features().rustc_attrs {
492 tcx.sess.track_errors(|| {
493 tcx.sess.time("outlives_testing", || outlives::test::test_inferred_outlives(tcx));
497 tcx.sess.track_errors(|| {
498 tcx.sess.time("impl_wf_inference", || {
499 tcx.hir().for_each_module(|module| tcx.ensure().check_mod_impl_wf(module))
503 tcx.sess.track_errors(|| {
504 tcx.sess.time("coherence_checking", || {
505 for &trait_def_id in tcx.all_local_trait_impls(()).keys() {
506 tcx.ensure().coherent_trait(trait_def_id);
509 // these queries are executed for side-effects (error reporting):
510 tcx.ensure().crate_inherent_impls(());
511 tcx.ensure().crate_inherent_impls_overlap_check(());
515 if tcx.features().rustc_attrs {
516 tcx.sess.track_errors(|| {
517 tcx.sess.time("variance_testing", || variance::test::test_variance(tcx));
521 tcx.sess.track_errors(|| {
522 tcx.sess.time("wf_checking", || {
523 tcx.hir().par_for_each_module(|module| tcx.ensure().check_mod_type_wf(module))
527 // NOTE: This is copy/pasted in librustdoc/core.rs and should be kept in sync.
528 tcx.sess.time("item_types_checking", || {
529 tcx.hir().for_each_module(|module| tcx.ensure().check_mod_item_types(module))
532 tcx.sess.time("item_bodies_checking", || tcx.typeck_item_bodies(()));
534 check_unused::check_crate(tcx);
535 check_for_entry_fn(tcx);
537 if let Some(reported) = tcx.sess.has_errors() { Err(reported) } else { Ok(()) }
540 /// A quasi-deprecated helper used in rustdoc and clippy to get
541 /// the type from a HIR node.
542 pub fn hir_ty_to_ty<'tcx>(tcx: TyCtxt<'tcx>, hir_ty: &hir::Ty<'_>) -> Ty<'tcx> {
543 // In case there are any projections, etc., find the "environment"
544 // def-ID that will be used to determine the traits/predicates in
545 // scope. This is derived from the enclosing item-like thing.
546 let env_def_id = tcx.hir().get_parent_item(hir_ty.hir_id);
547 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id.to_def_id());
548 item_cx.astconv().ast_ty_to_ty(hir_ty)
551 pub fn hir_trait_to_predicates<'tcx>(
553 hir_trait: &hir::TraitRef<'_>,
556 // In case there are any projections, etc., find the "environment"
557 // def-ID that will be used to determine the traits/predicates in
558 // scope. This is derived from the enclosing item-like thing.
559 let env_def_id = tcx.hir().get_parent_item(hir_trait.hir_ref_id);
560 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id.to_def_id());
561 let mut bounds = Bounds::default();
562 let _ = &item_cx.astconv().instantiate_poly_trait_ref(
565 ty::BoundConstness::NotConst,