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 #![cfg_attr(bootstrap, feature(label_break_value))]
68 #![feature(let_chains)]
69 #![cfg_attr(bootstrap, feature(let_else))]
70 #![feature(min_specialization)]
71 #![feature(never_type)]
72 #![feature(once_cell)]
73 #![feature(slice_partition_dedup)]
74 #![feature(try_blocks)]
75 #![feature(is_some_with)]
76 #![feature(type_alias_impl_trait)]
77 #![recursion_limit = "256"]
83 extern crate rustc_middle;
85 // These are used by Clippy.
87 pub mod expr_use_visitor;
94 mod constrained_generic_params;
98 mod mem_categorization;
100 mod structured_errors;
103 use rustc_errors::{struct_span_err, ErrorGuaranteed};
104 use rustc_hir as hir;
105 use rustc_hir::def_id::DefId;
106 use rustc_hir::{Node, CRATE_HIR_ID};
107 use rustc_infer::infer::{InferOk, TyCtxtInferExt};
108 use rustc_middle::middle;
109 use rustc_middle::ty::query::Providers;
110 use rustc_middle::ty::{self, Ty, TyCtxt};
111 use rustc_middle::util;
112 use rustc_session::config::EntryFnType;
113 use rustc_span::{symbol::sym, Span, DUMMY_SP};
114 use rustc_target::spec::abi::Abi;
115 use rustc_trait_selection::traits::error_reporting::InferCtxtExt as _;
116 use rustc_trait_selection::traits::{self, ObligationCause, ObligationCauseCode};
120 use astconv::AstConv;
123 fn require_c_abi_if_c_variadic(tcx: TyCtxt<'_>, decl: &hir::FnDecl<'_>, abi: Abi, span: Span) {
124 match (decl.c_variadic, abi) {
125 // The function has the correct calling convention, or isn't a "C-variadic" function.
126 (false, _) | (true, Abi::C { .. }) | (true, Abi::Cdecl { .. }) => {}
127 // The function is a "C-variadic" function with an incorrect calling convention.
129 let mut err = struct_span_err!(
133 "C-variadic function must have C or cdecl calling convention"
135 err.span_label(span, "C-variadics require C or cdecl calling convention").emit();
140 fn require_same_types<'tcx>(
142 cause: &ObligationCause<'tcx>,
146 tcx.infer_ctxt().enter(|ref infcx| {
147 let param_env = ty::ParamEnv::empty();
148 let errors = match infcx.at(cause, param_env).eq(expected, actual) {
149 Ok(InferOk { obligations, .. }) => traits::fully_solve_obligations(infcx, obligations),
151 infcx.report_mismatched_types(cause, expected, actual, err).emit();
159 infcx.report_fulfillment_errors(errors, None, false);
166 fn check_main_fn_ty(tcx: TyCtxt<'_>, main_def_id: DefId) {
167 let main_fnsig = tcx.fn_sig(main_def_id);
168 let main_span = tcx.def_span(main_def_id);
170 fn main_fn_diagnostics_hir_id(tcx: TyCtxt<'_>, def_id: DefId, sp: Span) -> hir::HirId {
171 if let Some(local_def_id) = def_id.as_local() {
172 let hir_id = tcx.hir().local_def_id_to_hir_id(local_def_id);
173 let hir_type = tcx.type_of(local_def_id);
174 if !matches!(hir_type.kind(), ty::FnDef(..)) {
175 span_bug!(sp, "main has a non-function type: found `{}`", hir_type);
183 fn main_fn_generics_params_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
184 if !def_id.is_local() {
187 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
188 match tcx.hir().find(hir_id) {
189 Some(Node::Item(hir::Item { kind: hir::ItemKind::Fn(_, ref generics, _), .. })) => {
190 if !generics.params.is_empty() {
197 span_bug!(tcx.def_span(def_id), "main has a non-function type");
202 fn main_fn_where_clauses_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
203 if !def_id.is_local() {
206 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
207 match tcx.hir().find(hir_id) {
208 Some(Node::Item(hir::Item { kind: hir::ItemKind::Fn(_, ref generics, _), .. })) => {
209 Some(generics.where_clause_span)
212 span_bug!(tcx.def_span(def_id), "main has a non-function type");
217 fn main_fn_asyncness_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
218 if !def_id.is_local() {
221 Some(tcx.def_span(def_id))
224 fn main_fn_return_type_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
225 if !def_id.is_local() {
228 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
229 match tcx.hir().find(hir_id) {
230 Some(Node::Item(hir::Item { kind: hir::ItemKind::Fn(ref fn_sig, _, _), .. })) => {
231 Some(fn_sig.decl.output.span())
234 span_bug!(tcx.def_span(def_id), "main has a non-function type");
239 let mut error = false;
240 let main_diagnostics_hir_id = main_fn_diagnostics_hir_id(tcx, main_def_id, main_span);
241 let main_fn_generics = tcx.generics_of(main_def_id);
242 let main_fn_predicates = tcx.predicates_of(main_def_id);
243 if main_fn_generics.count() != 0 || !main_fnsig.bound_vars().is_empty() {
244 let generics_param_span = main_fn_generics_params_span(tcx, main_def_id);
245 let msg = "`main` function is not allowed to have generic \
248 struct_span_err!(tcx.sess, generics_param_span.unwrap_or(main_span), E0131, "{}", msg);
249 if let Some(generics_param_span) = generics_param_span {
250 let label = "`main` cannot have generic parameters";
251 diag.span_label(generics_param_span, label);
255 } else if !main_fn_predicates.predicates.is_empty() {
256 // generics may bring in implicit predicates, so we skip this check if generics is present.
257 let generics_where_clauses_span = main_fn_where_clauses_span(tcx, main_def_id);
258 let mut diag = struct_span_err!(
260 generics_where_clauses_span.unwrap_or(main_span),
262 "`main` function is not allowed to have a `where` clause"
264 if let Some(generics_where_clauses_span) = generics_where_clauses_span {
265 diag.span_label(generics_where_clauses_span, "`main` cannot have a `where` clause");
271 let main_asyncness = tcx.asyncness(main_def_id);
272 if let hir::IsAsync::Async = main_asyncness {
273 let mut diag = struct_span_err!(
277 "`main` function is not allowed to be `async`"
279 let asyncness_span = main_fn_asyncness_span(tcx, main_def_id);
280 if let Some(asyncness_span) = asyncness_span {
281 diag.span_label(asyncness_span, "`main` function is not allowed to be `async`");
287 for attr in tcx.get_attrs(main_def_id, sym::track_caller) {
289 .struct_span_err(attr.span, "`main` function is not allowed to be `#[track_caller]`")
290 .span_label(main_span, "`main` function is not allowed to be `#[track_caller]`")
299 let expected_return_type;
300 if let Some(term_did) = tcx.lang_items().termination() {
301 let return_ty = main_fnsig.output();
302 let return_ty_span = main_fn_return_type_span(tcx, main_def_id).unwrap_or(main_span);
303 if !return_ty.bound_vars().is_empty() {
304 let msg = "`main` function return type is not allowed to have generic \
306 struct_span_err!(tcx.sess, return_ty_span, E0131, "{}", msg).emit();
309 let return_ty = return_ty.skip_binder();
310 tcx.infer_ctxt().enter(|infcx| {
311 // Main should have no WC, so empty param env is OK here.
312 let param_env = ty::ParamEnv::empty();
313 let cause = traits::ObligationCause::new(
315 main_diagnostics_hir_id,
316 ObligationCauseCode::MainFunctionType,
318 let ocx = traits::ObligationCtxt::new(&infcx);
319 let norm_return_ty = ocx.normalize(cause.clone(), param_env, return_ty);
320 ocx.register_bound(cause, param_env, norm_return_ty, term_did);
321 let errors = ocx.select_all_or_error();
322 if !errors.is_empty() {
323 infcx.report_fulfillment_errors(&errors, None, false);
327 // now we can take the return type of the given main function
328 expected_return_type = main_fnsig.output();
330 // standard () main return type
331 expected_return_type = ty::Binder::dummy(tcx.mk_unit());
338 let se_ty = tcx.mk_fn_ptr(expected_return_type.map_bound(|expected_return_type| {
339 tcx.mk_fn_sig(iter::empty(), expected_return_type, false, hir::Unsafety::Normal, Abi::Rust)
344 &ObligationCause::new(
346 main_diagnostics_hir_id,
347 ObligationCauseCode::MainFunctionType,
350 tcx.mk_fn_ptr(main_fnsig),
353 fn check_start_fn_ty(tcx: TyCtxt<'_>, start_def_id: DefId) {
354 let start_def_id = start_def_id.expect_local();
355 let start_id = tcx.hir().local_def_id_to_hir_id(start_def_id);
356 let start_span = tcx.def_span(start_def_id);
357 let start_t = tcx.type_of(start_def_id);
358 match start_t.kind() {
360 if let Some(Node::Item(it)) = tcx.hir().find(start_id) {
361 if let hir::ItemKind::Fn(ref sig, ref generics, _) = it.kind {
362 let mut error = false;
363 if !generics.params.is_empty() {
368 "start function is not allowed to have type parameters"
370 .span_label(generics.span, "start function cannot have type parameters")
374 if generics.has_where_clause_predicates {
377 generics.where_clause_span,
379 "start function is not allowed to have a `where` clause"
382 generics.where_clause_span,
383 "start function cannot have a `where` clause",
388 if let hir::IsAsync::Async = sig.header.asyncness {
389 let span = tcx.def_span(it.def_id);
394 "`start` is not allowed to be `async`"
396 .span_label(span, "`start` is not allowed to be `async`")
401 let attrs = tcx.hir().attrs(start_id);
403 if attr.has_name(sym::track_caller) {
407 "`start` is not allowed to be `#[track_caller]`",
411 "`start` is not allowed to be `#[track_caller]`",
424 let se_ty = tcx.mk_fn_ptr(ty::Binder::dummy(tcx.mk_fn_sig(
425 [tcx.types.isize, tcx.mk_imm_ptr(tcx.mk_imm_ptr(tcx.types.u8))].iter().cloned(),
428 hir::Unsafety::Normal,
434 &ObligationCause::new(start_span, start_id, ObligationCauseCode::StartFunctionType),
436 tcx.mk_fn_ptr(tcx.fn_sig(start_def_id)),
440 span_bug!(start_span, "start has a non-function type: found `{}`", start_t);
445 fn check_for_entry_fn(tcx: TyCtxt<'_>) {
446 match tcx.entry_fn(()) {
447 Some((def_id, EntryFnType::Main { .. })) => check_main_fn_ty(tcx, def_id),
448 Some((def_id, EntryFnType::Start)) => check_start_fn_ty(tcx, def_id),
453 pub fn provide(providers: &mut Providers) {
454 collect::provide(providers);
455 coherence::provide(providers);
456 check::provide(providers);
457 variance::provide(providers);
458 outlives::provide(providers);
459 impl_wf_check::provide(providers);
460 hir_wf_check::provide(providers);
463 pub fn check_crate(tcx: TyCtxt<'_>) -> Result<(), ErrorGuaranteed> {
464 let _prof_timer = tcx.sess.timer("type_check_crate");
466 // this ensures that later parts of type checking can assume that items
467 // have valid types and not error
468 // FIXME(matthewjasper) We shouldn't need to use `track_errors`.
469 tcx.sess.track_errors(|| {
470 tcx.sess.time("type_collecting", || {
471 tcx.hir().for_each_module(|module| tcx.ensure().collect_mod_item_types(module))
475 if tcx.features().rustc_attrs {
476 tcx.sess.track_errors(|| {
477 tcx.sess.time("outlives_testing", || outlives::test::test_inferred_outlives(tcx));
481 tcx.sess.track_errors(|| {
482 tcx.sess.time("impl_wf_inference", || {
483 tcx.hir().for_each_module(|module| tcx.ensure().check_mod_impl_wf(module))
487 tcx.sess.track_errors(|| {
488 tcx.sess.time("coherence_checking", || {
489 for &trait_def_id in tcx.all_local_trait_impls(()).keys() {
490 tcx.ensure().coherent_trait(trait_def_id);
493 // these queries are executed for side-effects (error reporting):
494 tcx.ensure().crate_inherent_impls(());
495 tcx.ensure().crate_inherent_impls_overlap_check(());
499 if tcx.features().rustc_attrs {
500 tcx.sess.track_errors(|| {
501 tcx.sess.time("variance_testing", || variance::test::test_variance(tcx));
505 tcx.sess.track_errors(|| {
506 tcx.sess.time("wf_checking", || {
507 tcx.hir().par_for_each_module(|module| tcx.ensure().check_mod_type_wf(module))
511 // NOTE: This is copy/pasted in librustdoc/core.rs and should be kept in sync.
512 tcx.sess.time("item_types_checking", || {
513 tcx.hir().for_each_module(|module| tcx.ensure().check_mod_item_types(module))
516 tcx.sess.time("item_bodies_checking", || tcx.typeck_item_bodies(()));
518 check_unused::check_crate(tcx);
519 check_for_entry_fn(tcx);
521 if let Some(reported) = tcx.sess.has_errors() { Err(reported) } else { Ok(()) }
524 /// A quasi-deprecated helper used in rustdoc and clippy to get
525 /// the type from a HIR node.
526 pub fn hir_ty_to_ty<'tcx>(tcx: TyCtxt<'tcx>, hir_ty: &hir::Ty<'_>) -> Ty<'tcx> {
527 // In case there are any projections, etc., find the "environment"
528 // def-ID that will be used to determine the traits/predicates in
529 // scope. This is derived from the enclosing item-like thing.
530 let env_def_id = tcx.hir().get_parent_item(hir_ty.hir_id);
531 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id.to_def_id());
532 <dyn AstConv<'_>>::ast_ty_to_ty(&item_cx, hir_ty)
535 pub fn hir_trait_to_predicates<'tcx>(
537 hir_trait: &hir::TraitRef<'_>,
540 // In case there are any projections, etc., find the "environment"
541 // def-ID that will be used to determine the traits/predicates in
542 // scope. This is derived from the enclosing item-like thing.
543 let env_def_id = tcx.hir().get_parent_item(hir_trait.hir_ref_id);
544 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id.to_def_id());
545 let mut bounds = Bounds::default();
546 let _ = <dyn AstConv<'_>>::instantiate_poly_trait_ref(
550 ty::BoundConstness::NotConst,