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)]
73 #![feature(once_cell)]
74 #![feature(slice_partition_dedup)]
75 #![feature(try_blocks)]
76 #![recursion_limit = "256"]
82 extern crate rustc_middle;
84 // These are used by Clippy.
86 pub mod expr_use_visitor;
93 mod constrained_generic_params;
97 mod mem_categorization;
99 mod structured_errors;
102 use rustc_errors::{struct_span_err, ErrorGuaranteed};
103 use rustc_hir as hir;
104 use rustc_hir::def_id::DefId;
105 use rustc_hir::{Node, CRATE_HIR_ID};
106 use rustc_infer::infer::{InferOk, TyCtxtInferExt};
107 use rustc_infer::traits::TraitEngineExt as _;
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::infer::InferCtxtExt;
116 use rustc_trait_selection::traits::error_reporting::InferCtxtExt as _;
117 use rustc_trait_selection::traits::{
118 self, ObligationCause, ObligationCauseCode, TraitEngine, TraitEngineExt as _,
123 use astconv::AstConv;
126 fn require_c_abi_if_c_variadic(tcx: TyCtxt<'_>, decl: &hir::FnDecl<'_>, abi: Abi, span: Span) {
127 match (decl.c_variadic, abi) {
128 // The function has the correct calling convention, or isn't a "C-variadic" function.
129 (false, _) | (true, Abi::C { .. }) | (true, Abi::Cdecl { .. }) => {}
130 // The function is a "C-variadic" function with an incorrect calling convention.
132 let mut err = struct_span_err!(
136 "C-variadic function must have C or cdecl calling convention"
138 err.span_label(span, "C-variadics require C or cdecl calling convention").emit();
143 fn require_same_types<'tcx>(
145 cause: &ObligationCause<'tcx>,
149 tcx.infer_ctxt().enter(|ref infcx| {
150 let param_env = ty::ParamEnv::empty();
151 let mut fulfill_cx = <dyn TraitEngine<'_>>::new(infcx.tcx);
152 match infcx.at(cause, param_env).eq(expected, actual) {
153 Ok(InferOk { obligations, .. }) => {
154 fulfill_cx.register_predicate_obligations(infcx, obligations);
157 infcx.report_mismatched_types(cause, expected, actual, err).emit();
162 match fulfill_cx.select_all_or_error(infcx).as_slice() {
165 infcx.report_fulfillment_errors(errors, None, false);
172 fn check_main_fn_ty(tcx: TyCtxt<'_>, main_def_id: DefId) {
173 let main_fnsig = tcx.fn_sig(main_def_id);
174 let main_span = tcx.def_span(main_def_id);
176 fn main_fn_diagnostics_hir_id(tcx: TyCtxt<'_>, def_id: DefId, sp: Span) -> hir::HirId {
177 if let Some(local_def_id) = def_id.as_local() {
178 let hir_id = tcx.hir().local_def_id_to_hir_id(local_def_id);
179 let hir_type = tcx.type_of(local_def_id);
180 if !matches!(hir_type.kind(), ty::FnDef(..)) {
181 span_bug!(sp, "main has a non-function type: found `{}`", hir_type);
189 fn main_fn_generics_params_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
190 if !def_id.is_local() {
193 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
194 match tcx.hir().find(hir_id) {
195 Some(Node::Item(hir::Item { kind: hir::ItemKind::Fn(_, ref generics, _), .. })) => {
196 if !generics.params.is_empty() {
203 span_bug!(tcx.def_span(def_id), "main has a non-function type");
208 fn main_fn_where_clauses_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
209 if !def_id.is_local() {
212 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
213 match tcx.hir().find(hir_id) {
214 Some(Node::Item(hir::Item { kind: hir::ItemKind::Fn(_, ref generics, _), .. })) => {
215 generics.where_clause_span()
218 span_bug!(tcx.def_span(def_id), "main has a non-function type");
223 fn main_fn_asyncness_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
224 if !def_id.is_local() {
227 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
228 match tcx.hir().find(hir_id) {
229 Some(Node::Item(hir::Item { span: item_span, .. })) => {
230 Some(tcx.sess.source_map().guess_head_span(*item_span))
233 span_bug!(tcx.def_span(def_id), "main has a non-function type");
238 fn main_fn_return_type_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
239 if !def_id.is_local() {
242 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
243 match tcx.hir().find(hir_id) {
244 Some(Node::Item(hir::Item { kind: hir::ItemKind::Fn(ref fn_sig, _, _), .. })) => {
245 Some(fn_sig.decl.output.span())
248 span_bug!(tcx.def_span(def_id), "main has a non-function type");
253 let mut error = false;
254 let main_diagnostics_hir_id = main_fn_diagnostics_hir_id(tcx, main_def_id, main_span);
255 let main_fn_generics = tcx.generics_of(main_def_id);
256 let main_fn_predicates = tcx.predicates_of(main_def_id);
257 if main_fn_generics.count() != 0 || !main_fnsig.bound_vars().is_empty() {
258 let generics_param_span = main_fn_generics_params_span(tcx, main_def_id);
259 let msg = "`main` function is not allowed to have generic \
262 struct_span_err!(tcx.sess, generics_param_span.unwrap_or(main_span), E0131, "{}", msg);
263 if let Some(generics_param_span) = generics_param_span {
264 let label = "`main` cannot have generic parameters".to_string();
265 diag.span_label(generics_param_span, label);
269 } else if !main_fn_predicates.predicates.is_empty() {
270 // generics may bring in implicit predicates, so we skip this check if generics is present.
271 let generics_where_clauses_span = main_fn_where_clauses_span(tcx, main_def_id);
272 let mut diag = struct_span_err!(
274 generics_where_clauses_span.unwrap_or(main_span),
276 "`main` function is not allowed to have a `where` clause"
278 if let Some(generics_where_clauses_span) = generics_where_clauses_span {
279 diag.span_label(generics_where_clauses_span, "`main` cannot have a `where` clause");
285 let main_asyncness = tcx.asyncness(main_def_id);
286 if let hir::IsAsync::Async = main_asyncness {
287 let mut diag = struct_span_err!(
291 "`main` function is not allowed to be `async`"
293 let asyncness_span = main_fn_asyncness_span(tcx, main_def_id);
294 if let Some(asyncness_span) = asyncness_span {
295 diag.span_label(asyncness_span, "`main` function is not allowed to be `async`");
301 for attr in tcx.get_attrs(main_def_id, sym::track_caller) {
303 .struct_span_err(attr.span, "`main` function is not allowed to be `#[track_caller]`")
304 .span_label(main_span, "`main` function is not allowed to be `#[track_caller]`")
313 let expected_return_type;
314 if let Some(term_id) = tcx.lang_items().termination() {
315 let return_ty = main_fnsig.output();
316 let return_ty_span = main_fn_return_type_span(tcx, main_def_id).unwrap_or(main_span);
317 if !return_ty.bound_vars().is_empty() {
318 let msg = "`main` function return type is not allowed to have generic \
321 struct_span_err!(tcx.sess, return_ty_span, E0131, "{}", msg).emit();
324 let return_ty = return_ty.skip_binder();
325 tcx.infer_ctxt().enter(|infcx| {
326 let cause = traits::ObligationCause::new(
328 main_diagnostics_hir_id,
329 ObligationCauseCode::MainFunctionType,
331 let mut fulfillment_cx = traits::FulfillmentContext::new();
332 // normalize any potential projections in the return type, then add
333 // any possible obligations to the fulfillment context.
334 // HACK(ThePuzzlemaker) this feels symptomatic of a problem within
335 // checking trait fulfillment, not this here. I'm not sure why it
336 // works in the example in `fn test()` given in #88609? This also
337 // probably isn't the best way to do this.
338 let InferOk { value: norm_return_ty, obligations } = infcx
339 .partially_normalize_associated_types_in(
341 ty::ParamEnv::empty(),
344 fulfillment_cx.register_predicate_obligations(&infcx, obligations);
345 fulfillment_cx.register_bound(
347 ty::ParamEnv::empty(),
352 let errors = fulfillment_cx.select_all_or_error(&infcx);
353 if !errors.is_empty() {
354 infcx.report_fulfillment_errors(&errors, None, false);
358 // now we can take the return type of the given main function
359 expected_return_type = main_fnsig.output();
361 // standard () main return type
362 expected_return_type = ty::Binder::dummy(tcx.mk_unit());
369 let se_ty = tcx.mk_fn_ptr(expected_return_type.map_bound(|expected_return_type| {
370 tcx.mk_fn_sig(iter::empty(), expected_return_type, false, hir::Unsafety::Normal, Abi::Rust)
375 &ObligationCause::new(
377 main_diagnostics_hir_id,
378 ObligationCauseCode::MainFunctionType,
381 tcx.mk_fn_ptr(main_fnsig),
384 fn check_start_fn_ty(tcx: TyCtxt<'_>, start_def_id: DefId) {
385 let start_def_id = start_def_id.expect_local();
386 let start_id = tcx.hir().local_def_id_to_hir_id(start_def_id);
387 let start_span = tcx.def_span(start_def_id);
388 let start_t = tcx.type_of(start_def_id);
389 match start_t.kind() {
391 if let Some(Node::Item(it)) = tcx.hir().find(start_id) {
392 if let hir::ItemKind::Fn(ref sig, ref generics, _) = it.kind {
393 let mut error = false;
394 if !generics.params.is_empty() {
399 "start function is not allowed to have type parameters"
401 .span_label(generics.span, "start function cannot have type parameters")
405 if let Some(sp) = generics.where_clause_span() {
410 "start function is not allowed to have a `where` clause"
412 .span_label(sp, "start function cannot have a `where` clause")
416 if let hir::IsAsync::Async = sig.header.asyncness {
417 let span = tcx.sess.source_map().guess_head_span(it.span);
422 "`start` is not allowed to be `async`"
424 .span_label(span, "`start` is not allowed to be `async`")
429 let attrs = tcx.hir().attrs(start_id);
431 if attr.has_name(sym::track_caller) {
435 "`start` is not allowed to be `#[track_caller]`",
439 "`start` is not allowed to be `#[track_caller]`",
452 let se_ty = tcx.mk_fn_ptr(ty::Binder::dummy(tcx.mk_fn_sig(
453 [tcx.types.isize, tcx.mk_imm_ptr(tcx.mk_imm_ptr(tcx.types.u8))].iter().cloned(),
456 hir::Unsafety::Normal,
462 &ObligationCause::new(start_span, start_id, ObligationCauseCode::StartFunctionType),
464 tcx.mk_fn_ptr(tcx.fn_sig(start_def_id)),
468 span_bug!(start_span, "start has a non-function type: found `{}`", start_t);
473 fn check_for_entry_fn(tcx: TyCtxt<'_>) {
474 match tcx.entry_fn(()) {
475 Some((def_id, EntryFnType::Main)) => check_main_fn_ty(tcx, def_id),
476 Some((def_id, EntryFnType::Start)) => check_start_fn_ty(tcx, def_id),
481 pub fn provide(providers: &mut Providers) {
482 collect::provide(providers);
483 coherence::provide(providers);
484 check::provide(providers);
485 variance::provide(providers);
486 outlives::provide(providers);
487 impl_wf_check::provide(providers);
488 hir_wf_check::provide(providers);
491 pub fn check_crate(tcx: TyCtxt<'_>) -> Result<(), ErrorGuaranteed> {
492 let _prof_timer = tcx.sess.timer("type_check_crate");
494 // this ensures that later parts of type checking can assume that items
495 // have valid types and not error
496 // FIXME(matthewjasper) We shouldn't need to use `track_errors`.
497 tcx.sess.track_errors(|| {
498 tcx.sess.time("type_collecting", || {
499 tcx.hir().for_each_module(|module| tcx.ensure().collect_mod_item_types(module))
503 if tcx.features().rustc_attrs {
504 tcx.sess.track_errors(|| {
505 tcx.sess.time("outlives_testing", || outlives::test::test_inferred_outlives(tcx));
509 tcx.sess.track_errors(|| {
510 tcx.sess.time("impl_wf_inference", || impl_wf_check::impl_wf_check(tcx));
513 tcx.sess.track_errors(|| {
514 tcx.sess.time("coherence_checking", || coherence::check_coherence(tcx));
517 if tcx.features().rustc_attrs {
518 tcx.sess.track_errors(|| {
519 tcx.sess.time("variance_testing", || variance::test::test_variance(tcx));
523 tcx.sess.track_errors(|| {
524 tcx.sess.time("wf_checking", || check::check_wf_new(tcx));
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 <dyn AstConv<'_>>::ast_ty_to_ty(&item_cx, 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 _ = <dyn AstConv<'_>>::instantiate_poly_trait_ref(
566 ty::BoundConstness::NotConst,