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(label_break_value)]
68 #![feature(let_chains)]
70 #![feature(min_specialization)]
71 #![feature(never_type)]
72 #![feature(once_cell)]
73 #![feature(slice_partition_dedup)]
74 #![feature(try_blocks)]
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_infer::traits::TraitEngineExt as _;
107 use rustc_middle::middle;
108 use rustc_middle::ty::query::Providers;
109 use rustc_middle::ty::{self, Ty, TyCtxt};
110 use rustc_middle::util;
111 use rustc_session::config::EntryFnType;
112 use rustc_span::{symbol::sym, Span, DUMMY_SP};
113 use rustc_target::spec::abi::Abi;
114 use rustc_trait_selection::infer::InferCtxtExt;
115 use rustc_trait_selection::traits::error_reporting::InferCtxtExt as _;
116 use rustc_trait_selection::traits::{
117 self, ObligationCause, ObligationCauseCode, TraitEngine, TraitEngineExt as _,
122 use astconv::AstConv;
125 fn require_c_abi_if_c_variadic(tcx: TyCtxt<'_>, decl: &hir::FnDecl<'_>, abi: Abi, span: Span) {
126 match (decl.c_variadic, abi) {
127 // The function has the correct calling convention, or isn't a "C-variadic" function.
128 (false, _) | (true, Abi::C { .. }) | (true, Abi::Cdecl { .. }) => {}
129 // The function is a "C-variadic" function with an incorrect calling convention.
131 let mut err = struct_span_err!(
135 "C-variadic function must have C or cdecl calling convention"
137 err.span_label(span, "C-variadics require C or cdecl calling convention").emit();
142 fn require_same_types<'tcx>(
144 cause: &ObligationCause<'tcx>,
148 tcx.infer_ctxt().enter(|ref infcx| {
149 let param_env = ty::ParamEnv::empty();
150 let mut fulfill_cx = <dyn TraitEngine<'_>>::new(infcx.tcx);
151 match infcx.at(cause, param_env).eq(expected, actual) {
152 Ok(InferOk { obligations, .. }) => {
153 fulfill_cx.register_predicate_obligations(infcx, obligations);
156 infcx.report_mismatched_types(cause, expected, actual, err).emit();
161 match fulfill_cx.select_all_or_error(infcx).as_slice() {
164 infcx.report_fulfillment_errors(errors, None, false);
171 fn check_main_fn_ty(tcx: TyCtxt<'_>, main_def_id: DefId) {
172 let main_fnsig = tcx.fn_sig(main_def_id);
173 let main_span = tcx.def_span(main_def_id);
175 fn main_fn_diagnostics_hir_id(tcx: TyCtxt<'_>, def_id: DefId, sp: Span) -> hir::HirId {
176 if let Some(local_def_id) = def_id.as_local() {
177 let hir_id = tcx.hir().local_def_id_to_hir_id(local_def_id);
178 let hir_type = tcx.type_of(local_def_id);
179 if !matches!(hir_type.kind(), ty::FnDef(..)) {
180 span_bug!(sp, "main has a non-function type: found `{}`", hir_type);
188 fn main_fn_generics_params_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
189 if !def_id.is_local() {
192 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
193 match tcx.hir().find(hir_id) {
194 Some(Node::Item(hir::Item { kind: hir::ItemKind::Fn(_, ref generics, _), .. })) => {
195 if !generics.params.is_empty() {
202 span_bug!(tcx.def_span(def_id), "main has a non-function type");
207 fn main_fn_where_clauses_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
208 if !def_id.is_local() {
211 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
212 match tcx.hir().find(hir_id) {
213 Some(Node::Item(hir::Item { kind: hir::ItemKind::Fn(_, ref generics, _), .. })) => {
214 Some(generics.where_clause_span)
217 span_bug!(tcx.def_span(def_id), "main has a non-function type");
222 fn main_fn_asyncness_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
223 if !def_id.is_local() {
226 Some(tcx.def_span(def_id))
229 fn main_fn_return_type_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
230 if !def_id.is_local() {
233 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
234 match tcx.hir().find(hir_id) {
235 Some(Node::Item(hir::Item { kind: hir::ItemKind::Fn(ref fn_sig, _, _), .. })) => {
236 Some(fn_sig.decl.output.span())
239 span_bug!(tcx.def_span(def_id), "main has a non-function type");
244 let mut error = false;
245 let main_diagnostics_hir_id = main_fn_diagnostics_hir_id(tcx, main_def_id, main_span);
246 let main_fn_generics = tcx.generics_of(main_def_id);
247 let main_fn_predicates = tcx.predicates_of(main_def_id);
248 if main_fn_generics.count() != 0 || !main_fnsig.bound_vars().is_empty() {
249 let generics_param_span = main_fn_generics_params_span(tcx, main_def_id);
250 let msg = "`main` function is not allowed to have generic \
253 struct_span_err!(tcx.sess, generics_param_span.unwrap_or(main_span), E0131, "{}", msg);
254 if let Some(generics_param_span) = generics_param_span {
255 let label = "`main` cannot have generic parameters".to_string();
256 diag.span_label(generics_param_span, label);
260 } else if !main_fn_predicates.predicates.is_empty() {
261 // generics may bring in implicit predicates, so we skip this check if generics is present.
262 let generics_where_clauses_span = main_fn_where_clauses_span(tcx, main_def_id);
263 let mut diag = struct_span_err!(
265 generics_where_clauses_span.unwrap_or(main_span),
267 "`main` function is not allowed to have a `where` clause"
269 if let Some(generics_where_clauses_span) = generics_where_clauses_span {
270 diag.span_label(generics_where_clauses_span, "`main` cannot have a `where` clause");
276 let main_asyncness = tcx.asyncness(main_def_id);
277 if let hir::IsAsync::Async = main_asyncness {
278 let mut diag = struct_span_err!(
282 "`main` function is not allowed to be `async`"
284 let asyncness_span = main_fn_asyncness_span(tcx, main_def_id);
285 if let Some(asyncness_span) = asyncness_span {
286 diag.span_label(asyncness_span, "`main` function is not allowed to be `async`");
292 for attr in tcx.get_attrs(main_def_id, sym::track_caller) {
294 .struct_span_err(attr.span, "`main` function is not allowed to be `#[track_caller]`")
295 .span_label(main_span, "`main` function is not allowed to be `#[track_caller]`")
304 let expected_return_type;
305 if let Some(term_id) = tcx.lang_items().termination() {
306 let return_ty = main_fnsig.output();
307 let return_ty_span = main_fn_return_type_span(tcx, main_def_id).unwrap_or(main_span);
308 if !return_ty.bound_vars().is_empty() {
309 let msg = "`main` function return type is not allowed to have generic \
312 struct_span_err!(tcx.sess, return_ty_span, E0131, "{}", msg).emit();
315 let return_ty = return_ty.skip_binder();
316 tcx.infer_ctxt().enter(|infcx| {
317 let cause = traits::ObligationCause::new(
319 main_diagnostics_hir_id,
320 ObligationCauseCode::MainFunctionType,
322 let mut fulfillment_cx = traits::FulfillmentContext::new();
323 // normalize any potential projections in the return type, then add
324 // any possible obligations to the fulfillment context.
325 // HACK(ThePuzzlemaker) this feels symptomatic of a problem within
326 // checking trait fulfillment, not this here. I'm not sure why it
327 // works in the example in `fn test()` given in #88609? This also
328 // probably isn't the best way to do this.
329 let InferOk { value: norm_return_ty, obligations } = infcx
330 .partially_normalize_associated_types_in(
332 ty::ParamEnv::empty(),
335 fulfillment_cx.register_predicate_obligations(&infcx, obligations);
336 fulfillment_cx.register_bound(
338 ty::ParamEnv::empty(),
343 let errors = fulfillment_cx.select_all_or_error(&infcx);
344 if !errors.is_empty() {
345 infcx.report_fulfillment_errors(&errors, None, false);
349 // now we can take the return type of the given main function
350 expected_return_type = main_fnsig.output();
352 // standard () main return type
353 expected_return_type = ty::Binder::dummy(tcx.mk_unit());
360 let se_ty = tcx.mk_fn_ptr(expected_return_type.map_bound(|expected_return_type| {
361 tcx.mk_fn_sig(iter::empty(), expected_return_type, false, hir::Unsafety::Normal, Abi::Rust)
366 &ObligationCause::new(
368 main_diagnostics_hir_id,
369 ObligationCauseCode::MainFunctionType,
372 tcx.mk_fn_ptr(main_fnsig),
375 fn check_start_fn_ty(tcx: TyCtxt<'_>, start_def_id: DefId) {
376 let start_def_id = start_def_id.expect_local();
377 let start_id = tcx.hir().local_def_id_to_hir_id(start_def_id);
378 let start_span = tcx.def_span(start_def_id);
379 let start_t = tcx.type_of(start_def_id);
380 match start_t.kind() {
382 if let Some(Node::Item(it)) = tcx.hir().find(start_id) {
383 if let hir::ItemKind::Fn(ref sig, ref generics, _) = it.kind {
384 let mut error = false;
385 if !generics.params.is_empty() {
390 "start function is not allowed to have type parameters"
392 .span_label(generics.span, "start function cannot have type parameters")
396 if generics.has_where_clause_predicates {
399 generics.where_clause_span,
401 "start function is not allowed to have a `where` clause"
404 generics.where_clause_span,
405 "start function cannot have a `where` clause",
410 if let hir::IsAsync::Async = sig.header.asyncness {
411 let span = tcx.def_span(it.def_id);
416 "`start` is not allowed to be `async`"
418 .span_label(span, "`start` is not allowed to be `async`")
423 let attrs = tcx.hir().attrs(start_id);
425 if attr.has_name(sym::track_caller) {
429 "`start` is not allowed to be `#[track_caller]`",
433 "`start` is not allowed to be `#[track_caller]`",
446 let se_ty = tcx.mk_fn_ptr(ty::Binder::dummy(tcx.mk_fn_sig(
447 [tcx.types.isize, tcx.mk_imm_ptr(tcx.mk_imm_ptr(tcx.types.u8))].iter().cloned(),
450 hir::Unsafety::Normal,
456 &ObligationCause::new(start_span, start_id, ObligationCauseCode::StartFunctionType),
458 tcx.mk_fn_ptr(tcx.fn_sig(start_def_id)),
462 span_bug!(start_span, "start has a non-function type: found `{}`", start_t);
467 fn check_for_entry_fn(tcx: TyCtxt<'_>) {
468 match tcx.entry_fn(()) {
469 Some((def_id, EntryFnType::Main)) => check_main_fn_ty(tcx, def_id),
470 Some((def_id, EntryFnType::Start)) => check_start_fn_ty(tcx, def_id),
475 pub fn provide(providers: &mut Providers) {
476 collect::provide(providers);
477 coherence::provide(providers);
478 check::provide(providers);
479 variance::provide(providers);
480 outlives::provide(providers);
481 impl_wf_check::provide(providers);
482 hir_wf_check::provide(providers);
485 pub fn check_crate(tcx: TyCtxt<'_>) -> Result<(), ErrorGuaranteed> {
486 let _prof_timer = tcx.sess.timer("type_check_crate");
488 // this ensures that later parts of type checking can assume that items
489 // have valid types and not error
490 // FIXME(matthewjasper) We shouldn't need to use `track_errors`.
491 tcx.sess.track_errors(|| {
492 tcx.sess.time("type_collecting", || {
493 tcx.hir().for_each_module(|module| tcx.ensure().collect_mod_item_types(module))
497 if tcx.features().rustc_attrs {
498 tcx.sess.track_errors(|| {
499 tcx.sess.time("outlives_testing", || outlives::test::test_inferred_outlives(tcx));
503 tcx.sess.track_errors(|| {
504 tcx.sess.time("impl_wf_inference", || {
505 tcx.hir().for_each_module(|module| tcx.ensure().check_mod_impl_wf(module))
509 tcx.sess.track_errors(|| {
510 tcx.sess.time("coherence_checking", || {
511 for &trait_def_id in tcx.all_local_trait_impls(()).keys() {
512 tcx.ensure().coherent_trait(trait_def_id);
515 // these queries are executed for side-effects (error reporting):
516 tcx.ensure().crate_inherent_impls(());
517 tcx.ensure().crate_inherent_impls_overlap_check(());
521 if tcx.features().rustc_attrs {
522 tcx.sess.track_errors(|| {
523 tcx.sess.time("variance_testing", || variance::test::test_variance(tcx));
527 tcx.sess.track_errors(|| {
528 tcx.sess.time("wf_checking", || {
529 tcx.hir().par_for_each_module(|module| tcx.ensure().check_mod_type_wf(module))
533 // NOTE: This is copy/pasted in librustdoc/core.rs and should be kept in sync.
534 tcx.sess.time("item_types_checking", || {
535 tcx.hir().for_each_module(|module| tcx.ensure().check_mod_item_types(module))
538 tcx.sess.time("item_bodies_checking", || tcx.typeck_item_bodies(()));
540 check_unused::check_crate(tcx);
541 check_for_entry_fn(tcx);
543 if let Some(reported) = tcx.sess.has_errors() { Err(reported) } else { Ok(()) }
546 /// A quasi-deprecated helper used in rustdoc and clippy to get
547 /// the type from a HIR node.
548 pub fn hir_ty_to_ty<'tcx>(tcx: TyCtxt<'tcx>, hir_ty: &hir::Ty<'_>) -> Ty<'tcx> {
549 // In case there are any projections, etc., find the "environment"
550 // def-ID that will be used to determine the traits/predicates in
551 // scope. This is derived from the enclosing item-like thing.
552 let env_def_id = tcx.hir().get_parent_item(hir_ty.hir_id);
553 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id.to_def_id());
554 <dyn AstConv<'_>>::ast_ty_to_ty(&item_cx, hir_ty)
557 pub fn hir_trait_to_predicates<'tcx>(
559 hir_trait: &hir::TraitRef<'_>,
562 // In case there are any projections, etc., find the "environment"
563 // def-ID that will be used to determine the traits/predicates in
564 // scope. This is derived from the enclosing item-like thing.
565 let env_def_id = tcx.hir().get_parent_item(hir_trait.hir_ref_id);
566 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id.to_def_id());
567 let mut bounds = Bounds::default();
568 let _ = <dyn AstConv<'_>>::instantiate_poly_trait_ref(
572 ty::BoundConstness::NotConst,