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;
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, parse::feature_err};
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 const ERROR_HEAD: &str = "C-variadic function must have a compatible calling convention";
123 const CONVENTIONS_UNSTABLE: &str = "`C`, `cdecl`, `win64`, `sysv64` or `efiapi`";
124 const CONVENTIONS_STABLE: &str = "`C` or `cdecl`";
125 const UNSTABLE_EXPLAIN: &str =
126 "using calling conventions other than `C` or `cdecl` for varargs functions is unstable";
128 if !decl.c_variadic || matches!(abi, Abi::C { .. } | Abi::Cdecl { .. }) {
132 let extended_abi_support = tcx.features().extended_varargs_abi_support;
133 let conventions = match (extended_abi_support, abi.supports_varargs()) {
134 // User enabled additional ABI support for varargs and function ABI matches those ones.
135 (true, true) => return,
137 // Using this ABI would be ok, if the feature for additional ABI support was enabled.
138 // Return CONVENTIONS_STABLE, because we want the other error to look the same.
141 &tcx.sess.parse_sess,
142 sym::extended_varargs_abi_support,
150 (false, false) => CONVENTIONS_STABLE,
151 (true, false) => CONVENTIONS_UNSTABLE,
154 let mut err = struct_span_err!(tcx.sess, span, E0045, "{}, like {}", ERROR_HEAD, conventions);
155 err.span_label(span, ERROR_HEAD).emit();
158 fn require_same_types<'tcx>(
160 cause: &ObligationCause<'tcx>,
164 let infcx = &tcx.infer_ctxt().build();
165 let param_env = ty::ParamEnv::empty();
166 let errors = match infcx.at(cause, param_env).eq(expected, actual) {
167 Ok(InferOk { obligations, .. }) => traits::fully_solve_obligations(infcx, obligations),
169 infcx.err_ctxt().report_mismatched_types(cause, expected, actual, err).emit();
177 infcx.err_ctxt().report_fulfillment_errors(errors, None);
183 fn check_main_fn_ty(tcx: TyCtxt<'_>, main_def_id: DefId) {
184 let main_fnsig = tcx.fn_sig(main_def_id);
185 let main_span = tcx.def_span(main_def_id);
187 fn main_fn_diagnostics_hir_id(tcx: TyCtxt<'_>, def_id: DefId, sp: Span) -> hir::HirId {
188 if let Some(local_def_id) = def_id.as_local() {
189 let hir_id = tcx.hir().local_def_id_to_hir_id(local_def_id);
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(_, ref generics, _), .. })) => {
207 if !generics.params.is_empty() {
214 span_bug!(tcx.def_span(def_id), "main has a non-function type");
219 fn main_fn_where_clauses_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
220 if !def_id.is_local() {
223 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
224 match tcx.hir().find(hir_id) {
225 Some(Node::Item(hir::Item { kind: hir::ItemKind::Fn(_, ref generics, _), .. })) => {
226 Some(generics.where_clause_span)
229 span_bug!(tcx.def_span(def_id), "main has a non-function type");
234 fn main_fn_asyncness_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
235 if !def_id.is_local() {
238 Some(tcx.def_span(def_id))
241 fn main_fn_return_type_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
242 if !def_id.is_local() {
245 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
246 match tcx.hir().find(hir_id) {
247 Some(Node::Item(hir::Item { kind: hir::ItemKind::Fn(ref fn_sig, _, _), .. })) => {
248 Some(fn_sig.decl.output.span())
251 span_bug!(tcx.def_span(def_id), "main has a non-function type");
256 let mut error = false;
257 let main_diagnostics_hir_id = main_fn_diagnostics_hir_id(tcx, main_def_id, main_span);
258 let main_fn_generics = tcx.generics_of(main_def_id);
259 let main_fn_predicates = tcx.predicates_of(main_def_id);
260 if main_fn_generics.count() != 0 || !main_fnsig.bound_vars().is_empty() {
261 let generics_param_span = main_fn_generics_params_span(tcx, main_def_id);
262 let msg = "`main` function is not allowed to have generic \
265 struct_span_err!(tcx.sess, generics_param_span.unwrap_or(main_span), E0131, "{}", msg);
266 if let Some(generics_param_span) = generics_param_span {
267 let label = "`main` cannot have generic parameters";
268 diag.span_label(generics_param_span, label);
272 } else if !main_fn_predicates.predicates.is_empty() {
273 // generics may bring in implicit predicates, so we skip this check if generics is present.
274 let generics_where_clauses_span = main_fn_where_clauses_span(tcx, main_def_id);
275 let mut diag = struct_span_err!(
277 generics_where_clauses_span.unwrap_or(main_span),
279 "`main` function is not allowed to have a `where` clause"
281 if let Some(generics_where_clauses_span) = generics_where_clauses_span {
282 diag.span_label(generics_where_clauses_span, "`main` cannot have a `where` clause");
288 let main_asyncness = tcx.asyncness(main_def_id);
289 if let hir::IsAsync::Async = main_asyncness {
290 let mut diag = struct_span_err!(
294 "`main` function is not allowed to be `async`"
296 let asyncness_span = main_fn_asyncness_span(tcx, main_def_id);
297 if let Some(asyncness_span) = asyncness_span {
298 diag.span_label(asyncness_span, "`main` function is not allowed to be `async`");
304 for attr in tcx.get_attrs(main_def_id, sym::track_caller) {
306 .struct_span_err(attr.span, "`main` function is not allowed to be `#[track_caller]`")
307 .span_label(main_span, "`main` function is not allowed to be `#[track_caller]`")
316 let expected_return_type;
317 if let Some(term_did) = tcx.lang_items().termination() {
318 let return_ty = main_fnsig.output();
319 let return_ty_span = main_fn_return_type_span(tcx, main_def_id).unwrap_or(main_span);
320 if !return_ty.bound_vars().is_empty() {
321 let msg = "`main` function return type is not allowed to have generic \
323 struct_span_err!(tcx.sess, return_ty_span, E0131, "{}", msg).emit();
326 let return_ty = return_ty.skip_binder();
327 let infcx = tcx.infer_ctxt().build();
328 // Main should have no WC, so empty param env is OK here.
329 let param_env = ty::ParamEnv::empty();
330 let cause = traits::ObligationCause::new(
332 main_diagnostics_hir_id,
333 ObligationCauseCode::MainFunctionType,
335 let ocx = traits::ObligationCtxt::new(&infcx);
336 let norm_return_ty = ocx.normalize(&cause, param_env, return_ty);
337 ocx.register_bound(cause, param_env, norm_return_ty, term_did);
338 let errors = ocx.select_all_or_error();
339 if !errors.is_empty() {
340 infcx.err_ctxt().report_fulfillment_errors(&errors, None);
343 // now we can take the return type of the given main function
344 expected_return_type = main_fnsig.output();
346 // standard () main return type
347 expected_return_type = ty::Binder::dummy(tcx.mk_unit());
354 let se_ty = tcx.mk_fn_ptr(expected_return_type.map_bound(|expected_return_type| {
355 tcx.mk_fn_sig(iter::empty(), expected_return_type, false, hir::Unsafety::Normal, Abi::Rust)
360 &ObligationCause::new(
362 main_diagnostics_hir_id,
363 ObligationCauseCode::MainFunctionType,
366 tcx.mk_fn_ptr(main_fnsig),
369 fn check_start_fn_ty(tcx: TyCtxt<'_>, start_def_id: DefId) {
370 let start_def_id = start_def_id.expect_local();
371 let start_id = tcx.hir().local_def_id_to_hir_id(start_def_id);
372 let start_span = tcx.def_span(start_def_id);
373 let start_t = tcx.type_of(start_def_id);
374 match start_t.kind() {
376 if let Some(Node::Item(it)) = tcx.hir().find(start_id) {
377 if let hir::ItemKind::Fn(ref sig, ref generics, _) = it.kind {
378 let mut error = false;
379 if !generics.params.is_empty() {
384 "start function is not allowed to have type parameters"
386 .span_label(generics.span, "start function cannot have type parameters")
390 if generics.has_where_clause_predicates {
393 generics.where_clause_span,
395 "start function is not allowed to have a `where` clause"
398 generics.where_clause_span,
399 "start function cannot have a `where` clause",
404 if let hir::IsAsync::Async = sig.header.asyncness {
405 let span = tcx.def_span(it.owner_id);
410 "`start` is not allowed to be `async`"
412 .span_label(span, "`start` is not allowed to be `async`")
417 let attrs = tcx.hir().attrs(start_id);
419 if attr.has_name(sym::track_caller) {
423 "`start` is not allowed to be `#[track_caller]`",
427 "`start` is not allowed to be `#[track_caller]`",
440 let se_ty = tcx.mk_fn_ptr(ty::Binder::dummy(tcx.mk_fn_sig(
441 [tcx.types.isize, tcx.mk_imm_ptr(tcx.mk_imm_ptr(tcx.types.u8))].iter().cloned(),
444 hir::Unsafety::Normal,
450 &ObligationCause::new(start_span, start_id, 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,