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 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
59 #![feature(bool_to_option)]
60 #![feature(crate_visibility_modifier)]
61 #![feature(format_args_capture)]
62 #![feature(if_let_guard)]
63 #![feature(in_band_lifetimes)]
64 #![feature(is_sorted)]
67 #![feature(try_blocks)]
68 #![feature(never_type)]
69 #![feature(slice_partition_dedup)]
70 #![feature(control_flow_enum)]
71 #![recursion_limit = "256"]
77 extern crate rustc_middle;
79 // These are used by Clippy.
81 pub mod expr_use_visitor;
88 mod constrained_generic_params;
92 mod mem_categorization;
94 mod structured_errors;
97 use rustc_errors::{struct_span_err, ErrorReported};
99 use rustc_hir::def_id::DefId;
100 use rustc_hir::{Node, CRATE_HIR_ID};
101 use rustc_infer::infer::{InferOk, TyCtxtInferExt};
102 use rustc_infer::traits::TraitEngineExt as _;
103 use rustc_middle::middle;
104 use rustc_middle::ty::query::Providers;
105 use rustc_middle::ty::{self, Ty, TyCtxt};
106 use rustc_middle::util;
107 use rustc_session::config::EntryFnType;
108 use rustc_span::{symbol::sym, Span, DUMMY_SP};
109 use rustc_target::spec::abi::Abi;
110 use rustc_trait_selection::infer::InferCtxtExt;
111 use rustc_trait_selection::traits::error_reporting::InferCtxtExt as _;
112 use rustc_trait_selection::traits::{
113 self, ObligationCause, ObligationCauseCode, TraitEngine, TraitEngineExt as _,
118 use astconv::AstConv;
121 fn require_c_abi_if_c_variadic(tcx: TyCtxt<'_>, decl: &hir::FnDecl<'_>, abi: Abi, span: Span) {
122 match (decl.c_variadic, abi) {
123 // The function has the correct calling convention, or isn't a "C-variadic" function.
124 (false, _) | (true, Abi::C { .. }) | (true, Abi::Cdecl) => {}
125 // The function is a "C-variadic" function with an incorrect calling convention.
127 let mut err = struct_span_err!(
131 "C-variadic function must have C or cdecl calling convention"
133 err.span_label(span, "C-variadics require C or cdecl calling convention").emit();
138 fn require_same_types<'tcx>(
140 cause: &ObligationCause<'tcx>,
144 tcx.infer_ctxt().enter(|ref infcx| {
145 let param_env = ty::ParamEnv::empty();
146 let mut fulfill_cx = <dyn TraitEngine<'_>>::new(infcx.tcx);
147 match infcx.at(cause, param_env).eq(expected, actual) {
148 Ok(InferOk { obligations, .. }) => {
149 fulfill_cx.register_predicate_obligations(infcx, obligations);
152 infcx.report_mismatched_types(cause, expected, actual, err).emit();
157 match fulfill_cx.select_all_or_error(infcx) {
160 infcx.report_fulfillment_errors(&errors, None, false);
167 fn check_main_fn_ty(tcx: TyCtxt<'_>, main_def_id: DefId) {
168 let main_fnsig = tcx.fn_sig(main_def_id);
169 let main_span = tcx.def_span(main_def_id);
171 fn main_fn_diagnostics_hir_id(tcx: TyCtxt<'_>, def_id: DefId, sp: Span) -> hir::HirId {
172 if let Some(local_def_id) = def_id.as_local() {
173 let hir_id = tcx.hir().local_def_id_to_hir_id(local_def_id);
174 let hir_type = tcx.type_of(local_def_id);
175 if !matches!(hir_type.kind(), ty::FnDef(..)) {
176 span_bug!(sp, "main has a non-function type: found `{}`", hir_type);
184 fn main_fn_generics_params_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
185 if !def_id.is_local() {
188 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
189 match tcx.hir().find(hir_id) {
190 Some(Node::Item(hir::Item { kind: hir::ItemKind::Fn(_, ref generics, _), .. })) => {
191 if !generics.params.is_empty() {
198 span_bug!(tcx.def_span(def_id), "main has a non-function type");
203 fn main_fn_where_clauses_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
204 if !def_id.is_local() {
207 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
208 match tcx.hir().find(hir_id) {
209 Some(Node::Item(hir::Item { kind: hir::ItemKind::Fn(_, ref generics, _), .. })) => {
210 generics.where_clause.span()
213 span_bug!(tcx.def_span(def_id), "main has a non-function type");
218 fn main_fn_asyncness_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
219 if !def_id.is_local() {
222 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
223 match tcx.hir().find(hir_id) {
224 Some(Node::Item(hir::Item { span: item_span, .. })) => {
225 Some(tcx.sess.source_map().guess_head_span(*item_span))
228 span_bug!(tcx.def_span(def_id), "main has a non-function type");
233 fn main_fn_return_type_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
234 if !def_id.is_local() {
237 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
238 match tcx.hir().find(hir_id) {
239 Some(Node::Item(hir::Item { kind: hir::ItemKind::Fn(ref fn_sig, _, _), .. })) => {
240 Some(fn_sig.decl.output.span())
243 span_bug!(tcx.def_span(def_id), "main has a non-function type");
248 let mut error = false;
249 let main_diagnostics_hir_id = main_fn_diagnostics_hir_id(tcx, main_def_id, main_span);
250 let main_fn_generics = tcx.generics_of(main_def_id);
251 let main_fn_predicates = tcx.predicates_of(main_def_id);
252 if main_fn_generics.count() != 0 || !main_fnsig.bound_vars().is_empty() {
253 let generics_param_span = main_fn_generics_params_span(tcx, main_def_id);
254 let msg = "`main` function is not allowed to have generic \
257 struct_span_err!(tcx.sess, generics_param_span.unwrap_or(main_span), E0131, "{}", msg);
258 if let Some(generics_param_span) = generics_param_span {
259 let label = "`main` cannot have generic parameters".to_string();
260 diag.span_label(generics_param_span, label);
264 } else if !main_fn_predicates.predicates.is_empty() {
265 // generics may bring in implicit predicates, so we skip this check if generics is present.
266 let generics_where_clauses_span = main_fn_where_clauses_span(tcx, main_def_id);
267 let mut diag = struct_span_err!(
269 generics_where_clauses_span.unwrap_or(main_span),
271 "`main` function is not allowed to have a `where` clause"
273 if let Some(generics_where_clauses_span) = generics_where_clauses_span {
274 diag.span_label(generics_where_clauses_span, "`main` cannot have a `where` clause");
280 let main_asyncness = tcx.asyncness(main_def_id);
281 if let hir::IsAsync::Async = main_asyncness {
282 let mut diag = struct_span_err!(
286 "`main` function is not allowed to be `async`"
288 let asyncness_span = main_fn_asyncness_span(tcx, main_def_id);
289 if let Some(asyncness_span) = asyncness_span {
290 diag.span_label(asyncness_span, "`main` function is not allowed to be `async`");
296 for attr in tcx.get_attrs(main_def_id) {
297 if attr.has_name(sym::track_caller) {
301 "`main` function is not allowed to be `#[track_caller]`",
303 .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 if let Err(err) = fulfillment_cx.select_all_or_error(&infcx) {
353 infcx.report_fulfillment_errors(&err, None, false);
357 // now we can take the return type of the given main function
358 expected_return_type = main_fnsig.output();
360 // standard () main return type
361 expected_return_type = ty::Binder::dummy(tcx.mk_unit());
368 let se_ty = tcx.mk_fn_ptr(expected_return_type.map_bound(|expected_return_type| {
369 tcx.mk_fn_sig(iter::empty(), expected_return_type, false, hir::Unsafety::Normal, Abi::Rust)
374 &ObligationCause::new(
376 main_diagnostics_hir_id,
377 ObligationCauseCode::MainFunctionType,
380 tcx.mk_fn_ptr(main_fnsig),
383 fn check_start_fn_ty(tcx: TyCtxt<'_>, start_def_id: DefId) {
384 let start_def_id = start_def_id.expect_local();
385 let start_id = tcx.hir().local_def_id_to_hir_id(start_def_id);
386 let start_span = tcx.def_span(start_def_id);
387 let start_t = tcx.type_of(start_def_id);
388 match start_t.kind() {
390 if let Some(Node::Item(it)) = tcx.hir().find(start_id) {
391 if let hir::ItemKind::Fn(ref sig, ref generics, _) = it.kind {
392 let mut error = false;
393 if !generics.params.is_empty() {
398 "start function is not allowed to have type parameters"
400 .span_label(generics.span, "start function cannot have type parameters")
404 if let Some(sp) = generics.where_clause.span() {
409 "start function is not allowed to have a `where` clause"
411 .span_label(sp, "start function cannot have a `where` clause")
415 if let hir::IsAsync::Async = sig.header.asyncness {
416 let span = tcx.sess.source_map().guess_head_span(it.span);
421 "`start` is not allowed to be `async`"
423 .span_label(span, "`start` is not allowed to be `async`")
428 let attrs = tcx.hir().attrs(start_id);
430 if attr.has_name(sym::track_caller) {
434 "`start` is not allowed to be `#[track_caller]`",
438 "`start` is not allowed to be `#[track_caller]`",
451 let se_ty = tcx.mk_fn_ptr(ty::Binder::dummy(tcx.mk_fn_sig(
452 [tcx.types.isize, tcx.mk_imm_ptr(tcx.mk_imm_ptr(tcx.types.u8))].iter().cloned(),
455 hir::Unsafety::Normal,
461 &ObligationCause::new(start_span, start_id, ObligationCauseCode::StartFunctionType),
463 tcx.mk_fn_ptr(tcx.fn_sig(start_def_id)),
467 span_bug!(start_span, "start has a non-function type: found `{}`", start_t);
472 fn check_for_entry_fn(tcx: TyCtxt<'_>) {
473 match tcx.entry_fn(()) {
474 Some((def_id, EntryFnType::Main)) => check_main_fn_ty(tcx, def_id),
475 Some((def_id, EntryFnType::Start)) => check_start_fn_ty(tcx, def_id),
480 pub fn provide(providers: &mut Providers) {
481 collect::provide(providers);
482 coherence::provide(providers);
483 check::provide(providers);
484 variance::provide(providers);
485 outlives::provide(providers);
486 impl_wf_check::provide(providers);
487 hir_wf_check::provide(providers);
490 pub fn check_crate(tcx: TyCtxt<'_>) -> Result<(), ErrorReported> {
491 let _prof_timer = tcx.sess.timer("type_check_crate");
493 // this ensures that later parts of type checking can assume that items
494 // have valid types and not error
495 // FIXME(matthewjasper) We shouldn't need to use `track_errors`.
496 tcx.sess.track_errors(|| {
497 tcx.sess.time("type_collecting", || {
498 tcx.hir().for_each_module(|module| tcx.ensure().collect_mod_item_types(module))
502 if tcx.features().rustc_attrs {
503 tcx.sess.track_errors(|| {
504 tcx.sess.time("outlives_testing", || outlives::test::test_inferred_outlives(tcx));
508 tcx.sess.track_errors(|| {
509 tcx.sess.time("impl_wf_inference", || impl_wf_check::impl_wf_check(tcx));
512 tcx.sess.track_errors(|| {
513 tcx.sess.time("coherence_checking", || coherence::check_coherence(tcx));
516 if tcx.features().rustc_attrs {
517 tcx.sess.track_errors(|| {
518 tcx.sess.time("variance_testing", || variance::test::test_variance(tcx));
522 tcx.sess.track_errors(|| {
523 tcx.sess.time("wf_checking", || check::check_wf_new(tcx));
526 // NOTE: This is copy/pasted in librustdoc/core.rs and should be kept in sync.
527 tcx.sess.time("item_types_checking", || {
528 tcx.hir().for_each_module(|module| tcx.ensure().check_mod_item_types(module))
531 tcx.sess.time("item_bodies_checking", || tcx.typeck_item_bodies(()));
533 check_unused::check_crate(tcx);
534 check_for_entry_fn(tcx);
536 if tcx.sess.err_count() == 0 { Ok(()) } else { Err(ErrorReported) }
539 /// A quasi-deprecated helper used in rustdoc and clippy to get
540 /// the type from a HIR node.
541 pub fn hir_ty_to_ty<'tcx>(tcx: TyCtxt<'tcx>, hir_ty: &hir::Ty<'_>) -> Ty<'tcx> {
542 // In case there are any projections, etc., find the "environment"
543 // def-ID that will be used to determine the traits/predicates in
544 // scope. This is derived from the enclosing item-like thing.
545 let env_node_id = tcx.hir().get_parent_item(hir_ty.hir_id);
546 let env_def_id = tcx.hir().local_def_id(env_node_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_hir_id = tcx.hir().get_parent_item(hir_trait.hir_ref_id);
560 let env_def_id = tcx.hir().local_def_id(env_hir_id);
561 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id.to_def_id());
562 let mut bounds = Bounds::default();
563 let _ = <dyn AstConv<'_>>::instantiate_poly_trait_ref(
567 ty::BoundConstness::NotConst,