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)]
66 #![feature(min_specialization)]
68 #![feature(try_blocks)]
69 #![feature(never_type)]
70 #![feature(slice_partition_dedup)]
71 #![feature(control_flow_enum)]
72 #![recursion_limit = "256"]
78 extern crate rustc_middle;
80 // These are used by Clippy.
82 pub mod expr_use_visitor;
89 mod constrained_generic_params;
93 mod mem_categorization;
95 mod structured_errors;
98 use rustc_errors::{struct_span_err, ErrorReported};
100 use rustc_hir::def_id::DefId;
101 use rustc_hir::{Node, CRATE_HIR_ID};
102 use rustc_infer::infer::{InferOk, TyCtxtInferExt};
103 use rustc_infer::traits::TraitEngineExt as _;
104 use rustc_middle::middle;
105 use rustc_middle::ty::query::Providers;
106 use rustc_middle::ty::{self, Ty, TyCtxt};
107 use rustc_middle::util;
108 use rustc_session::config::EntryFnType;
109 use rustc_span::{symbol::sym, Span, DUMMY_SP};
110 use rustc_target::spec::abi::Abi;
111 use rustc_trait_selection::infer::InferCtxtExt;
112 use rustc_trait_selection::traits::error_reporting::InferCtxtExt as _;
113 use rustc_trait_selection::traits::{
114 self, ObligationCause, ObligationCauseCode, TraitEngine, TraitEngineExt as _,
119 use astconv::AstConv;
122 fn require_c_abi_if_c_variadic(tcx: TyCtxt<'_>, decl: &hir::FnDecl<'_>, abi: Abi, span: Span) {
123 match (decl.c_variadic, abi) {
124 // The function has the correct calling convention, or isn't a "C-variadic" function.
125 (false, _) | (true, Abi::C { .. }) | (true, Abi::Cdecl) => {}
126 // The function is a "C-variadic" function with an incorrect calling convention.
128 let mut err = struct_span_err!(
132 "C-variadic function must have C or cdecl calling convention"
134 err.span_label(span, "C-variadics require C or cdecl calling convention").emit();
139 fn require_same_types<'tcx>(
141 cause: &ObligationCause<'tcx>,
145 tcx.infer_ctxt().enter(|ref infcx| {
146 let param_env = ty::ParamEnv::empty();
147 let mut fulfill_cx = <dyn TraitEngine<'_>>::new(infcx.tcx);
148 match infcx.at(cause, param_env).eq(expected, actual) {
149 Ok(InferOk { obligations, .. }) => {
150 fulfill_cx.register_predicate_obligations(infcx, obligations);
153 infcx.report_mismatched_types(cause, expected, actual, err).emit();
158 match fulfill_cx.select_all_or_error(infcx) {
161 infcx.report_fulfillment_errors(&errors, None, false);
168 fn check_main_fn_ty(tcx: TyCtxt<'_>, main_def_id: DefId) {
169 let main_fnsig = tcx.fn_sig(main_def_id);
170 let main_span = tcx.def_span(main_def_id);
172 fn main_fn_diagnostics_hir_id(tcx: TyCtxt<'_>, def_id: DefId, sp: Span) -> hir::HirId {
173 if let Some(local_def_id) = def_id.as_local() {
174 let hir_id = tcx.hir().local_def_id_to_hir_id(local_def_id);
175 let hir_type = tcx.type_of(local_def_id);
176 if !matches!(hir_type.kind(), ty::FnDef(..)) {
177 span_bug!(sp, "main has a non-function type: found `{}`", hir_type);
185 fn main_fn_generics_params_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
186 if !def_id.is_local() {
189 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
190 match tcx.hir().find(hir_id) {
191 Some(Node::Item(hir::Item { kind: hir::ItemKind::Fn(_, ref generics, _), .. })) => {
192 if !generics.params.is_empty() {
199 span_bug!(tcx.def_span(def_id), "main has a non-function type");
204 fn main_fn_where_clauses_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
205 if !def_id.is_local() {
208 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
209 match tcx.hir().find(hir_id) {
210 Some(Node::Item(hir::Item { kind: hir::ItemKind::Fn(_, ref generics, _), .. })) => {
211 generics.where_clause.span()
214 span_bug!(tcx.def_span(def_id), "main has a non-function type");
219 fn main_fn_asyncness_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 { span: item_span, .. })) => {
226 Some(tcx.sess.source_map().guess_head_span(*item_span))
229 span_bug!(tcx.def_span(def_id), "main has a non-function type");
234 fn main_fn_return_type_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
235 if !def_id.is_local() {
238 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
239 match tcx.hir().find(hir_id) {
240 Some(Node::Item(hir::Item { kind: hir::ItemKind::Fn(ref fn_sig, _, _), .. })) => {
241 Some(fn_sig.decl.output.span())
244 span_bug!(tcx.def_span(def_id), "main has a non-function type");
249 let mut error = false;
250 let main_diagnostics_hir_id = main_fn_diagnostics_hir_id(tcx, main_def_id, main_span);
251 let main_fn_generics = tcx.generics_of(main_def_id);
252 let main_fn_predicates = tcx.predicates_of(main_def_id);
253 if main_fn_generics.count() != 0 || !main_fnsig.bound_vars().is_empty() {
254 let generics_param_span = main_fn_generics_params_span(tcx, main_def_id);
255 let msg = "`main` function is not allowed to have generic \
258 struct_span_err!(tcx.sess, generics_param_span.unwrap_or(main_span), E0131, "{}", msg);
259 if let Some(generics_param_span) = generics_param_span {
260 let label = "`main` cannot have generic parameters".to_string();
261 diag.span_label(generics_param_span, label);
265 } else if !main_fn_predicates.predicates.is_empty() {
266 // generics may bring in implicit predicates, so we skip this check if generics is present.
267 let generics_where_clauses_span = main_fn_where_clauses_span(tcx, main_def_id);
268 let mut diag = struct_span_err!(
270 generics_where_clauses_span.unwrap_or(main_span),
272 "`main` function is not allowed to have a `where` clause"
274 if let Some(generics_where_clauses_span) = generics_where_clauses_span {
275 diag.span_label(generics_where_clauses_span, "`main` cannot have a `where` clause");
281 let main_asyncness = tcx.asyncness(main_def_id);
282 if let hir::IsAsync::Async = main_asyncness {
283 let mut diag = struct_span_err!(
287 "`main` function is not allowed to be `async`"
289 let asyncness_span = main_fn_asyncness_span(tcx, main_def_id);
290 if let Some(asyncness_span) = asyncness_span {
291 diag.span_label(asyncness_span, "`main` function is not allowed to be `async`");
297 for attr in tcx.get_attrs(main_def_id) {
298 if attr.has_name(sym::track_caller) {
302 "`main` function is not allowed to be `#[track_caller]`",
304 .span_label(main_span, "`main` function is not allowed to be `#[track_caller]`")
314 let expected_return_type;
315 if let Some(term_id) = tcx.lang_items().termination() {
316 let return_ty = main_fnsig.output();
317 let return_ty_span = main_fn_return_type_span(tcx, main_def_id).unwrap_or(main_span);
318 if !return_ty.bound_vars().is_empty() {
319 let msg = "`main` function return type is not allowed to have generic \
322 struct_span_err!(tcx.sess, return_ty_span, E0131, "{}", msg).emit();
325 let return_ty = return_ty.skip_binder();
326 tcx.infer_ctxt().enter(|infcx| {
327 let cause = traits::ObligationCause::new(
329 main_diagnostics_hir_id,
330 ObligationCauseCode::MainFunctionType,
332 let mut fulfillment_cx = traits::FulfillmentContext::new();
333 // normalize any potential projections in the return type, then add
334 // any possible obligations to the fulfillment context.
335 // HACK(ThePuzzlemaker) this feels symptomatic of a problem within
336 // checking trait fulfillment, not this here. I'm not sure why it
337 // works in the example in `fn test()` given in #88609? This also
338 // probably isn't the best way to do this.
339 let InferOk { value: norm_return_ty, obligations } = infcx
340 .partially_normalize_associated_types_in(
342 ty::ParamEnv::empty(),
345 fulfillment_cx.register_predicate_obligations(&infcx, obligations);
346 fulfillment_cx.register_bound(
348 ty::ParamEnv::empty(),
353 if let Err(err) = fulfillment_cx.select_all_or_error(&infcx) {
354 infcx.report_fulfillment_errors(&err, 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<(), ErrorReported> {
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 tcx.sess.err_count() == 0 { Ok(()) } else { Err(ErrorReported) }
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_node_id = tcx.hir().get_parent_item(hir_ty.hir_id);
547 let env_def_id = tcx.hir().local_def_id(env_node_id);
548 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id.to_def_id());
549 <dyn AstConv<'_>>::ast_ty_to_ty(&item_cx, hir_ty)
552 pub fn hir_trait_to_predicates<'tcx>(
554 hir_trait: &hir::TraitRef<'_>,
557 // In case there are any projections, etc., find the "environment"
558 // def-ID that will be used to determine the traits/predicates in
559 // scope. This is derived from the enclosing item-like thing.
560 let env_hir_id = tcx.hir().get_parent_item(hir_trait.hir_ref_id);
561 let env_def_id = tcx.hir().local_def_id(env_hir_id);
562 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id.to_def_id());
563 let mut bounds = Bounds::default();
564 let _ = <dyn AstConv<'_>>::instantiate_poly_trait_ref(
568 ty::BoundConstness::NotConst,