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 #![cfg_attr(bootstrap, feature(label_break_value))]
69 #![feature(min_specialization)]
70 #![feature(never_type)]
71 #![feature(once_cell)]
72 #![feature(slice_partition_dedup)]
73 #![feature(try_blocks)]
74 #![feature(is_some_with)]
75 #![feature(type_alias_impl_trait)]
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_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::traits::error_reporting::InferCtxtExt as _;
115 use rustc_trait_selection::traits::{self, ObligationCause, ObligationCauseCode};
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 errors = match infcx.at(cause, param_env).eq(expected, actual) {
148 Ok(InferOk { obligations, .. }) => traits::fully_solve_obligations(infcx, obligations),
150 infcx.report_mismatched_types(cause, expected, actual, err).emit();
158 infcx.report_fulfillment_errors(errors, None, false);
165 fn check_main_fn_ty(tcx: TyCtxt<'_>, main_def_id: DefId) {
166 let main_fnsig = tcx.fn_sig(main_def_id);
167 let main_span = tcx.def_span(main_def_id);
169 fn main_fn_diagnostics_hir_id(tcx: TyCtxt<'_>, def_id: DefId, sp: Span) -> hir::HirId {
170 if let Some(local_def_id) = def_id.as_local() {
171 let hir_id = tcx.hir().local_def_id_to_hir_id(local_def_id);
172 let hir_type = tcx.type_of(local_def_id);
173 if !matches!(hir_type.kind(), ty::FnDef(..)) {
174 span_bug!(sp, "main has a non-function type: found `{}`", hir_type);
182 fn main_fn_generics_params_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
183 if !def_id.is_local() {
186 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
187 match tcx.hir().find(hir_id) {
188 Some(Node::Item(hir::Item { kind: hir::ItemKind::Fn(_, ref generics, _), .. })) => {
189 if !generics.params.is_empty() {
196 span_bug!(tcx.def_span(def_id), "main has a non-function type");
201 fn main_fn_where_clauses_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
202 if !def_id.is_local() {
205 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
206 match tcx.hir().find(hir_id) {
207 Some(Node::Item(hir::Item { kind: hir::ItemKind::Fn(_, ref generics, _), .. })) => {
208 Some(generics.where_clause_span)
211 span_bug!(tcx.def_span(def_id), "main has a non-function type");
216 fn main_fn_asyncness_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
217 if !def_id.is_local() {
220 Some(tcx.def_span(def_id))
223 fn main_fn_return_type_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 { kind: hir::ItemKind::Fn(ref fn_sig, _, _), .. })) => {
230 Some(fn_sig.decl.output.span())
233 span_bug!(tcx.def_span(def_id), "main has a non-function type");
238 let mut error = false;
239 let main_diagnostics_hir_id = main_fn_diagnostics_hir_id(tcx, main_def_id, main_span);
240 let main_fn_generics = tcx.generics_of(main_def_id);
241 let main_fn_predicates = tcx.predicates_of(main_def_id);
242 if main_fn_generics.count() != 0 || !main_fnsig.bound_vars().is_empty() {
243 let generics_param_span = main_fn_generics_params_span(tcx, main_def_id);
244 let msg = "`main` function is not allowed to have generic \
247 struct_span_err!(tcx.sess, generics_param_span.unwrap_or(main_span), E0131, "{}", msg);
248 if let Some(generics_param_span) = generics_param_span {
249 let label = "`main` cannot have generic parameters";
250 diag.span_label(generics_param_span, label);
254 } else if !main_fn_predicates.predicates.is_empty() {
255 // generics may bring in implicit predicates, so we skip this check if generics is present.
256 let generics_where_clauses_span = main_fn_where_clauses_span(tcx, main_def_id);
257 let mut diag = struct_span_err!(
259 generics_where_clauses_span.unwrap_or(main_span),
261 "`main` function is not allowed to have a `where` clause"
263 if let Some(generics_where_clauses_span) = generics_where_clauses_span {
264 diag.span_label(generics_where_clauses_span, "`main` cannot have a `where` clause");
270 let main_asyncness = tcx.asyncness(main_def_id);
271 if let hir::IsAsync::Async = main_asyncness {
272 let mut diag = struct_span_err!(
276 "`main` function is not allowed to be `async`"
278 let asyncness_span = main_fn_asyncness_span(tcx, main_def_id);
279 if let Some(asyncness_span) = asyncness_span {
280 diag.span_label(asyncness_span, "`main` function is not allowed to be `async`");
286 for attr in tcx.get_attrs(main_def_id, sym::track_caller) {
288 .struct_span_err(attr.span, "`main` function is not allowed to be `#[track_caller]`")
289 .span_label(main_span, "`main` function is not allowed to be `#[track_caller]`")
298 let expected_return_type;
299 if let Some(term_did) = tcx.lang_items().termination() {
300 let return_ty = main_fnsig.output();
301 let return_ty_span = main_fn_return_type_span(tcx, main_def_id).unwrap_or(main_span);
302 if !return_ty.bound_vars().is_empty() {
303 let msg = "`main` function return type is not allowed to have generic \
305 struct_span_err!(tcx.sess, return_ty_span, E0131, "{}", msg).emit();
308 let return_ty = return_ty.skip_binder();
309 tcx.infer_ctxt().enter(|infcx| {
310 // Main should have no WC, so empty param env is OK here.
311 let param_env = ty::ParamEnv::empty();
312 let cause = traits::ObligationCause::new(
314 main_diagnostics_hir_id,
315 ObligationCauseCode::MainFunctionType,
317 let ocx = traits::ObligationCtxt::new(&infcx);
318 let norm_return_ty = ocx.normalize(cause.clone(), param_env, return_ty);
319 ocx.register_bound(cause, param_env, norm_return_ty, term_did);
320 let errors = ocx.select_all_or_error();
321 if !errors.is_empty() {
322 infcx.report_fulfillment_errors(&errors, None, false);
326 // now we can take the return type of the given main function
327 expected_return_type = main_fnsig.output();
329 // standard () main return type
330 expected_return_type = ty::Binder::dummy(tcx.mk_unit());
337 let se_ty = tcx.mk_fn_ptr(expected_return_type.map_bound(|expected_return_type| {
338 tcx.mk_fn_sig(iter::empty(), expected_return_type, false, hir::Unsafety::Normal, Abi::Rust)
343 &ObligationCause::new(
345 main_diagnostics_hir_id,
346 ObligationCauseCode::MainFunctionType,
349 tcx.mk_fn_ptr(main_fnsig),
352 fn check_start_fn_ty(tcx: TyCtxt<'_>, start_def_id: DefId) {
353 let start_def_id = start_def_id.expect_local();
354 let start_id = tcx.hir().local_def_id_to_hir_id(start_def_id);
355 let start_span = tcx.def_span(start_def_id);
356 let start_t = tcx.type_of(start_def_id);
357 match start_t.kind() {
359 if let Some(Node::Item(it)) = tcx.hir().find(start_id) {
360 if let hir::ItemKind::Fn(ref sig, ref generics, _) = it.kind {
361 let mut error = false;
362 if !generics.params.is_empty() {
367 "start function is not allowed to have type parameters"
369 .span_label(generics.span, "start function cannot have type parameters")
373 if generics.has_where_clause_predicates {
376 generics.where_clause_span,
378 "start function is not allowed to have a `where` clause"
381 generics.where_clause_span,
382 "start function cannot have a `where` clause",
387 if let hir::IsAsync::Async = sig.header.asyncness {
388 let span = tcx.def_span(it.def_id);
393 "`start` is not allowed to be `async`"
395 .span_label(span, "`start` is not allowed to be `async`")
400 let attrs = tcx.hir().attrs(start_id);
402 if attr.has_name(sym::track_caller) {
406 "`start` is not allowed to be `#[track_caller]`",
410 "`start` is not allowed to be `#[track_caller]`",
423 let se_ty = tcx.mk_fn_ptr(ty::Binder::dummy(tcx.mk_fn_sig(
424 [tcx.types.isize, tcx.mk_imm_ptr(tcx.mk_imm_ptr(tcx.types.u8))].iter().cloned(),
427 hir::Unsafety::Normal,
433 &ObligationCause::new(start_span, start_id, ObligationCauseCode::StartFunctionType),
435 tcx.mk_fn_ptr(tcx.fn_sig(start_def_id)),
439 span_bug!(start_span, "start has a non-function type: found `{}`", start_t);
444 fn check_for_entry_fn(tcx: TyCtxt<'_>) {
445 match tcx.entry_fn(()) {
446 Some((def_id, EntryFnType::Main)) => check_main_fn_ty(tcx, def_id),
447 Some((def_id, EntryFnType::Start)) => check_start_fn_ty(tcx, def_id),
452 pub fn provide(providers: &mut Providers) {
453 collect::provide(providers);
454 coherence::provide(providers);
455 check::provide(providers);
456 variance::provide(providers);
457 outlives::provide(providers);
458 impl_wf_check::provide(providers);
459 hir_wf_check::provide(providers);
462 pub fn check_crate(tcx: TyCtxt<'_>) -> Result<(), ErrorGuaranteed> {
463 let _prof_timer = tcx.sess.timer("type_check_crate");
465 // this ensures that later parts of type checking can assume that items
466 // have valid types and not error
467 // FIXME(matthewjasper) We shouldn't need to use `track_errors`.
468 tcx.sess.track_errors(|| {
469 tcx.sess.time("type_collecting", || {
470 tcx.hir().for_each_module(|module| tcx.ensure().collect_mod_item_types(module))
474 if tcx.features().rustc_attrs {
475 tcx.sess.track_errors(|| {
476 tcx.sess.time("outlives_testing", || outlives::test::test_inferred_outlives(tcx));
480 tcx.sess.track_errors(|| {
481 tcx.sess.time("impl_wf_inference", || {
482 tcx.hir().for_each_module(|module| tcx.ensure().check_mod_impl_wf(module))
486 tcx.sess.track_errors(|| {
487 tcx.sess.time("coherence_checking", || {
488 for &trait_def_id in tcx.all_local_trait_impls(()).keys() {
489 tcx.ensure().coherent_trait(trait_def_id);
492 // these queries are executed for side-effects (error reporting):
493 tcx.ensure().crate_inherent_impls(());
494 tcx.ensure().crate_inherent_impls_overlap_check(());
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", || {
506 tcx.hir().par_for_each_module(|module| tcx.ensure().check_mod_type_wf(module))
510 // NOTE: This is copy/pasted in librustdoc/core.rs and should be kept in sync.
511 tcx.sess.time("item_types_checking", || {
512 tcx.hir().for_each_module(|module| 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 let Some(reported) = tcx.sess.has_errors() { Err(reported) } else { Ok(()) }
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_def_id = tcx.hir().get_parent_item(hir_ty.hir_id);
530 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id.to_def_id());
531 <dyn AstConv<'_>>::ast_ty_to_ty(&item_cx, hir_ty)
534 pub fn hir_trait_to_predicates<'tcx>(
536 hir_trait: &hir::TraitRef<'_>,
539 // In case there are any projections, etc., find the "environment"
540 // def-ID that will be used to determine the traits/predicates in
541 // scope. This is derived from the enclosing item-like thing.
542 let env_def_id = tcx.hir().get_parent_item(hir_trait.hir_ref_id);
543 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id.to_def_id());
544 let mut bounds = Bounds::default();
545 let _ = <dyn AstConv<'_>>::instantiate_poly_trait_ref(
549 ty::BoundConstness::NotConst,