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 #![cfg_attr(bootstrap, feature(bindings_after_at))]
60 #![feature(bool_to_option)]
61 #![feature(crate_visibility_modifier)]
62 #![feature(format_args_capture)]
63 #![feature(if_let_guard)]
64 #![feature(in_band_lifetimes)]
65 #![feature(is_sorted)]
68 #![feature(try_blocks)]
69 #![feature(never_type)]
70 #![feature(slice_partition_dedup)]
71 #![feature(control_flow_enum)]
72 #![cfg_attr(bootstrap, allow(incomplete_features))] // if_let_guard
73 #![recursion_limit = "256"]
79 extern crate rustc_middle;
81 // These are used by Clippy.
83 pub mod expr_use_visitor;
90 mod constrained_generic_params;
94 mod mem_categorization;
96 mod structured_errors;
99 use rustc_errors::{struct_span_err, ErrorReported};
100 use rustc_hir as hir;
101 use rustc_hir::def_id::DefId;
102 use rustc_hir::{Node, CRATE_HIR_ID};
103 use rustc_infer::infer::{InferOk, TyCtxtInferExt};
104 use rustc_infer::traits::TraitEngineExt as _;
105 use rustc_middle::middle;
106 use rustc_middle::ty::query::Providers;
107 use rustc_middle::ty::{self, Ty, TyCtxt};
108 use rustc_middle::util;
109 use rustc_session::config::EntryFnType;
110 use rustc_span::{symbol::sym, Span, DUMMY_SP};
111 use rustc_target::spec::abi::Abi;
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 let generics_param_span =
193 if !generics.params.is_empty() { Some(generics.span) } else { None };
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 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 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
222 match tcx.hir().find(hir_id) {
223 Some(Node::Item(hir::Item { span: item_span, .. })) => {
224 Some(tcx.sess.source_map().guess_head_span(*item_span))
227 span_bug!(tcx.def_span(def_id), "main has a non-function type");
232 fn main_fn_return_type_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
233 if !def_id.is_local() {
236 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
237 match tcx.hir().find(hir_id) {
238 Some(Node::Item(hir::Item { kind: hir::ItemKind::Fn(ref fn_sig, _, _), .. })) => {
239 Some(fn_sig.decl.output.span())
242 span_bug!(tcx.def_span(def_id), "main has a non-function type");
247 let mut error = false;
248 let main_diagnostics_hir_id = main_fn_diagnostics_hir_id(tcx, main_def_id, main_span);
249 let main_fn_generics = tcx.generics_of(main_def_id);
250 let main_fn_predicates = tcx.predicates_of(main_def_id);
251 if main_fn_generics.count() != 0 || !main_fnsig.bound_vars().is_empty() {
252 let generics_param_span = main_fn_generics_params_span(tcx, main_def_id);
253 let msg = "`main` function is not allowed to have generic \
256 struct_span_err!(tcx.sess, generics_param_span.unwrap_or(main_span), E0131, "{}", msg);
257 if let Some(generics_param_span) = generics_param_span {
258 let label = "`main` cannot have generic parameters".to_string();
259 diag.span_label(generics_param_span, label);
263 } else if !main_fn_predicates.predicates.is_empty() {
264 // generics may bring in implicit predicates, so we skip this check if generics is present.
265 let generics_where_clauses_span = main_fn_where_clauses_span(tcx, main_def_id);
266 let mut diag = struct_span_err!(
268 generics_where_clauses_span.unwrap_or(main_span),
270 "`main` function is not allowed to have a `where` clause"
272 if let Some(generics_where_clauses_span) = generics_where_clauses_span {
273 diag.span_label(generics_where_clauses_span, "`main` cannot have a `where` clause");
279 let main_asyncness = tcx.asyncness(main_def_id);
280 if let hir::IsAsync::Async = main_asyncness {
281 let mut diag = struct_span_err!(
285 "`main` function is not allowed to be `async`"
287 let asyncness_span = main_fn_asyncness_span(tcx, main_def_id);
288 if let Some(asyncness_span) = asyncness_span {
289 diag.span_label(asyncness_span, "`main` function is not allowed to be `async`");
295 for attr in tcx.get_attrs(main_def_id) {
296 if attr.has_name(sym::track_caller) {
300 "`main` function is not allowed to be `#[track_caller]`",
302 .span_label(main_span, "`main` function is not allowed to be `#[track_caller]`")
312 let expected_return_type;
313 if let Some(term_id) = tcx.lang_items().termination() {
314 let return_ty = main_fnsig.output();
315 let return_ty_span = main_fn_return_type_span(tcx, main_def_id).unwrap_or(main_span);
316 if !return_ty.bound_vars().is_empty() {
317 let msg = "`main` function return type is not allowed to have generic \
320 struct_span_err!(tcx.sess, return_ty_span, E0131, "{}", msg).emit();
323 let return_ty = return_ty.skip_binder();
324 tcx.infer_ctxt().enter(|infcx| {
325 let cause = traits::ObligationCause::new(
327 main_diagnostics_hir_id,
328 ObligationCauseCode::MainFunctionType,
330 let mut fulfillment_cx = traits::FulfillmentContext::new();
331 fulfillment_cx.register_bound(&infcx, ty::ParamEnv::empty(), return_ty, term_id, cause);
332 if let Err(err) = fulfillment_cx.select_all_or_error(&infcx) {
333 infcx.report_fulfillment_errors(&err, None, false);
337 // now we can take the return type of the given main function
338 expected_return_type = main_fnsig.output();
340 // standard () main return type
341 expected_return_type = ty::Binder::dummy(tcx.mk_unit());
348 let se_ty = tcx.mk_fn_ptr(expected_return_type.map_bound(|expected_return_type| {
349 tcx.mk_fn_sig(iter::empty(), expected_return_type, false, hir::Unsafety::Normal, Abi::Rust)
354 &ObligationCause::new(
356 main_diagnostics_hir_id,
357 ObligationCauseCode::MainFunctionType,
360 tcx.mk_fn_ptr(main_fnsig),
363 fn check_start_fn_ty(tcx: TyCtxt<'_>, start_def_id: DefId) {
364 let start_def_id = start_def_id.expect_local();
365 let start_id = tcx.hir().local_def_id_to_hir_id(start_def_id);
366 let start_span = tcx.def_span(start_def_id);
367 let start_t = tcx.type_of(start_def_id);
368 match start_t.kind() {
370 if let Some(Node::Item(it)) = tcx.hir().find(start_id) {
371 if let hir::ItemKind::Fn(ref sig, ref generics, _) = it.kind {
372 let mut error = false;
373 if !generics.params.is_empty() {
378 "start function is not allowed to have type parameters"
380 .span_label(generics.span, "start function cannot have type parameters")
384 if let Some(sp) = generics.where_clause.span() {
389 "start function is not allowed to have a `where` clause"
391 .span_label(sp, "start function cannot have a `where` clause")
395 if let hir::IsAsync::Async = sig.header.asyncness {
396 let span = tcx.sess.source_map().guess_head_span(it.span);
401 "`start` is not allowed to be `async`"
403 .span_label(span, "`start` is not allowed to be `async`")
408 let attrs = tcx.hir().attrs(start_id);
410 if attr.has_name(sym::track_caller) {
414 "`start` is not allowed to be `#[track_caller]`",
418 "`start` is not allowed to be `#[track_caller]`",
431 let se_ty = tcx.mk_fn_ptr(ty::Binder::dummy(tcx.mk_fn_sig(
432 [tcx.types.isize, tcx.mk_imm_ptr(tcx.mk_imm_ptr(tcx.types.u8))].iter().cloned(),
435 hir::Unsafety::Normal,
441 &ObligationCause::new(start_span, start_id, ObligationCauseCode::StartFunctionType),
443 tcx.mk_fn_ptr(tcx.fn_sig(start_def_id)),
447 span_bug!(start_span, "start has a non-function type: found `{}`", start_t);
452 fn check_for_entry_fn(tcx: TyCtxt<'_>) {
453 match tcx.entry_fn(()) {
454 Some((def_id, EntryFnType::Main)) => check_main_fn_ty(tcx, def_id),
455 Some((def_id, EntryFnType::Start)) => check_start_fn_ty(tcx, def_id),
460 pub fn provide(providers: &mut Providers) {
461 collect::provide(providers);
462 coherence::provide(providers);
463 check::provide(providers);
464 variance::provide(providers);
465 outlives::provide(providers);
466 impl_wf_check::provide(providers);
467 hir_wf_check::provide(providers);
470 pub fn check_crate(tcx: TyCtxt<'_>) -> Result<(), ErrorReported> {
471 let _prof_timer = tcx.sess.timer("type_check_crate");
473 // this ensures that later parts of type checking can assume that items
474 // have valid types and not error
475 // FIXME(matthewjasper) We shouldn't need to use `track_errors`.
476 tcx.sess.track_errors(|| {
477 tcx.sess.time("type_collecting", || {
478 for &module in tcx.hir().krate().modules.keys() {
479 tcx.ensure().collect_mod_item_types(module);
484 if tcx.features().rustc_attrs {
485 tcx.sess.track_errors(|| {
486 tcx.sess.time("outlives_testing", || outlives::test::test_inferred_outlives(tcx));
490 tcx.sess.track_errors(|| {
491 tcx.sess.time("impl_wf_inference", || impl_wf_check::impl_wf_check(tcx));
494 tcx.sess.track_errors(|| {
495 tcx.sess.time("coherence_checking", || coherence::check_coherence(tcx));
498 if tcx.features().rustc_attrs {
499 tcx.sess.track_errors(|| {
500 tcx.sess.time("variance_testing", || variance::test::test_variance(tcx));
504 tcx.sess.track_errors(|| {
505 tcx.sess.time("wf_checking", || check::check_wf_new(tcx));
508 // NOTE: This is copy/pasted in librustdoc/core.rs and should be kept in sync.
509 tcx.sess.time("item_types_checking", || {
510 for &module in tcx.hir().krate().modules.keys() {
511 tcx.ensure().check_mod_item_types(module);
515 tcx.sess.time("item_bodies_checking", || tcx.typeck_item_bodies(()));
517 check_unused::check_crate(tcx);
518 check_for_entry_fn(tcx);
520 if tcx.sess.err_count() == 0 { Ok(()) } else { Err(ErrorReported) }
523 /// A quasi-deprecated helper used in rustdoc and clippy to get
524 /// the type from a HIR node.
525 pub fn hir_ty_to_ty<'tcx>(tcx: TyCtxt<'tcx>, hir_ty: &hir::Ty<'_>) -> Ty<'tcx> {
526 // In case there are any projections, etc., find the "environment"
527 // def-ID that will be used to determine the traits/predicates in
528 // scope. This is derived from the enclosing item-like thing.
529 let env_node_id = tcx.hir().get_parent_item(hir_ty.hir_id);
530 let env_def_id = tcx.hir().local_def_id(env_node_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_hir_id = tcx.hir().get_parent_item(hir_trait.hir_ref_id);
544 let env_def_id = tcx.hir().local_def_id(env_hir_id);
545 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id.to_def_id());
546 let mut bounds = Bounds::default();
547 let _ = <dyn AstConv<'_>>::instantiate_poly_trait_ref(
551 ty::BoundConstness::NotConst,