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(bindings_after_at)]
60 #![feature(bool_to_option)]
61 #![feature(box_syntax)]
62 #![feature(crate_visibility_modifier)]
63 #![feature(format_args_capture)]
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 #![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;
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::traits::error_reporting::InferCtxtExt as _;
111 use rustc_trait_selection::traits::{
112 self, ObligationCause, ObligationCauseCode, TraitEngine, TraitEngineExt as _,
117 use astconv::AstConv;
120 fn require_c_abi_if_c_variadic(tcx: TyCtxt<'_>, decl: &hir::FnDecl<'_>, abi: Abi, span: Span) {
121 match (decl.c_variadic, abi) {
122 // The function has the correct calling convention, or isn't a "C-variadic" function.
123 (false, _) | (true, Abi::C { .. }) | (true, Abi::Cdecl) => {}
124 // The function is a "C-variadic" function with an incorrect calling convention.
126 let mut err = struct_span_err!(
130 "C-variadic function must have C or cdecl calling convention"
132 err.span_label(span, "C-variadics require C or cdecl calling convention").emit();
137 fn require_same_types<'tcx>(
139 cause: &ObligationCause<'tcx>,
143 tcx.infer_ctxt().enter(|ref infcx| {
144 let param_env = ty::ParamEnv::empty();
145 let mut fulfill_cx = <dyn TraitEngine<'_>>::new(infcx.tcx);
146 match infcx.at(&cause, param_env).eq(expected, actual) {
147 Ok(InferOk { obligations, .. }) => {
148 fulfill_cx.register_predicate_obligations(infcx, obligations);
151 infcx.report_mismatched_types(cause, expected, actual, err).emit();
156 match fulfill_cx.select_all_or_error(infcx) {
159 infcx.report_fulfillment_errors(&errors, None, false);
166 fn check_main_fn_ty(tcx: TyCtxt<'_>, main_def_id: DefId) {
167 let main_fnsig = tcx.fn_sig(main_def_id);
168 let main_span = tcx.def_span(main_def_id);
170 fn main_fn_diagnostics_hir_id(tcx: TyCtxt<'_>, def_id: DefId, sp: Span) -> hir::HirId {
171 if let Some(local_def_id) = def_id.as_local() {
172 let hir_id = tcx.hir().local_def_id_to_hir_id(local_def_id);
173 let hir_type = tcx.type_of(local_def_id);
174 if !matches!(hir_type.kind(), ty::FnDef(..)) {
175 span_bug!(sp, "main has a non-function type: found `{}`", hir_type);
183 fn main_fn_generics_params_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
184 if !def_id.is_local() {
187 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
188 match tcx.hir().find(hir_id) {
189 Some(Node::Item(hir::Item { kind: hir::ItemKind::Fn(_, ref generics, _), .. })) => {
190 let generics_param_span =
191 if !generics.params.is_empty() { Some(generics.span) } else { None };
195 span_bug!(tcx.def_span(def_id), "main has a non-function type");
200 fn main_fn_where_clauses_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
201 if !def_id.is_local() {
204 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
205 match tcx.hir().find(hir_id) {
206 Some(Node::Item(hir::Item { kind: hir::ItemKind::Fn(_, ref generics, _), .. })) => {
207 generics.where_clause.span()
210 span_bug!(tcx.def_span(def_id), "main has a non-function type");
215 fn main_fn_asyncness_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
216 if !def_id.is_local() {
219 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
220 match tcx.hir().find(hir_id) {
221 Some(Node::Item(hir::Item { span: item_span, .. })) => {
222 Some(tcx.sess.source_map().guess_head_span(*item_span))
225 span_bug!(tcx.def_span(def_id), "main has a non-function type");
230 fn main_fn_return_type_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
231 if !def_id.is_local() {
234 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
235 match tcx.hir().find(hir_id) {
236 Some(Node::Item(hir::Item { kind: hir::ItemKind::Fn(ref fn_sig, _, _), .. })) => {
237 Some(fn_sig.decl.output.span())
240 span_bug!(tcx.def_span(def_id), "main has a non-function type");
245 let mut error = false;
246 let main_diagnostics_hir_id = main_fn_diagnostics_hir_id(tcx, main_def_id, main_span);
247 let main_fn_generics = tcx.generics_of(main_def_id);
248 let main_fn_predicates = tcx.predicates_of(main_def_id);
249 if main_fn_generics.count() != 0 || !main_fnsig.bound_vars().is_empty() {
250 let generics_param_span = main_fn_generics_params_span(tcx, main_def_id);
251 let msg = "`main` function is not allowed to have generic \
254 struct_span_err!(tcx.sess, generics_param_span.unwrap_or(main_span), E0131, "{}", msg);
255 if let Some(generics_param_span) = generics_param_span {
256 let label = "`main` cannot have generic parameters".to_string();
257 diag.span_label(generics_param_span, label);
261 } else if !main_fn_predicates.predicates.is_empty() {
262 // generics may bring in implicit predicates, so we skip this check if generics is present.
263 let generics_where_clauses_span = main_fn_where_clauses_span(tcx, main_def_id);
264 let mut diag = struct_span_err!(
266 generics_where_clauses_span.unwrap_or(main_span),
268 "`main` function is not allowed to have a `where` clause"
270 if let Some(generics_where_clauses_span) = generics_where_clauses_span {
271 diag.span_label(generics_where_clauses_span, "`main` cannot have a `where` clause");
277 let main_asyncness = tcx.asyncness(main_def_id);
278 if let hir::IsAsync::Async = main_asyncness {
279 let mut diag = struct_span_err!(
283 "`main` function is not allowed to be `async`"
285 let asyncness_span = main_fn_asyncness_span(tcx, main_def_id);
286 if let Some(asyncness_span) = asyncness_span {
287 diag.span_label(asyncness_span, "`main` function is not allowed to be `async`");
293 for attr in tcx.get_attrs(main_def_id) {
294 if tcx.sess.check_name(attr, sym::track_caller) {
298 "`main` function is not allowed to be `#[track_caller]`",
300 .span_label(main_span, "`main` function is not allowed to be `#[track_caller]`")
310 let expected_return_type;
311 if let Some(term_id) = tcx.lang_items().termination() {
312 let return_ty = main_fnsig.output();
313 let return_ty_span = main_fn_return_type_span(tcx, main_def_id).unwrap_or(main_span);
314 if !return_ty.bound_vars().is_empty() {
315 let msg = "`main` function return type is not allowed to have generic \
318 struct_span_err!(tcx.sess, return_ty_span, E0131, "{}", msg).emit();
321 let return_ty = return_ty.skip_binder();
322 tcx.infer_ctxt().enter(|infcx| {
323 let cause = traits::ObligationCause::new(
325 main_diagnostics_hir_id,
326 ObligationCauseCode::MainFunctionType,
328 let mut fulfillment_cx = traits::FulfillmentContext::new();
329 fulfillment_cx.register_bound(&infcx, ty::ParamEnv::empty(), return_ty, term_id, cause);
330 if let Err(err) = fulfillment_cx.select_all_or_error(&infcx) {
331 infcx.report_fulfillment_errors(&err, None, false);
335 // now we can take the return type of the given main function
336 expected_return_type = main_fnsig.output();
338 // standard () main return type
339 expected_return_type = ty::Binder::dummy(tcx.mk_unit());
346 let se_ty = tcx.mk_fn_ptr(expected_return_type.map_bound(|expected_return_type| {
347 tcx.mk_fn_sig(iter::empty(), expected_return_type, false, hir::Unsafety::Normal, Abi::Rust)
352 &ObligationCause::new(
354 main_diagnostics_hir_id,
355 ObligationCauseCode::MainFunctionType,
358 tcx.mk_fn_ptr(main_fnsig),
361 fn check_start_fn_ty(tcx: TyCtxt<'_>, start_def_id: DefId) {
362 let start_def_id = start_def_id.expect_local();
363 let start_id = tcx.hir().local_def_id_to_hir_id(start_def_id);
364 let start_span = tcx.def_span(start_def_id);
365 let start_t = tcx.type_of(start_def_id);
366 match start_t.kind() {
368 if let Some(Node::Item(it)) = tcx.hir().find(start_id) {
369 if let hir::ItemKind::Fn(ref sig, ref generics, _) = it.kind {
370 let mut error = false;
371 if !generics.params.is_empty() {
376 "start function is not allowed to have type parameters"
378 .span_label(generics.span, "start function cannot have type parameters")
382 if let Some(sp) = generics.where_clause.span() {
387 "start function is not allowed to have a `where` clause"
389 .span_label(sp, "start function cannot have a `where` clause")
393 if let hir::IsAsync::Async = sig.header.asyncness {
394 let span = tcx.sess.source_map().guess_head_span(it.span);
399 "`start` is not allowed to be `async`"
401 .span_label(span, "`start` is not allowed to be `async`")
406 let attrs = tcx.hir().attrs(start_id);
408 if tcx.sess.check_name(attr, sym::track_caller) {
412 "`start` is not allowed to be `#[track_caller]`",
416 "`start` is not allowed to be `#[track_caller]`",
429 let se_ty = tcx.mk_fn_ptr(ty::Binder::dummy(tcx.mk_fn_sig(
430 [tcx.types.isize, tcx.mk_imm_ptr(tcx.mk_imm_ptr(tcx.types.u8))].iter().cloned(),
433 hir::Unsafety::Normal,
439 &ObligationCause::new(start_span, start_id, ObligationCauseCode::StartFunctionType),
441 tcx.mk_fn_ptr(tcx.fn_sig(start_def_id)),
445 span_bug!(start_span, "start has a non-function type: found `{}`", start_t);
450 fn check_for_entry_fn(tcx: TyCtxt<'_>) {
451 match tcx.entry_fn(()) {
452 Some((def_id, EntryFnType::Main)) => check_main_fn_ty(tcx, def_id),
453 Some((def_id, EntryFnType::Start)) => check_start_fn_ty(tcx, def_id),
458 pub fn provide(providers: &mut Providers) {
459 collect::provide(providers);
460 coherence::provide(providers);
461 check::provide(providers);
462 variance::provide(providers);
463 outlives::provide(providers);
464 impl_wf_check::provide(providers);
467 pub fn check_crate(tcx: TyCtxt<'_>) -> Result<(), ErrorReported> {
468 let _prof_timer = tcx.sess.timer("type_check_crate");
470 // this ensures that later parts of type checking can assume that items
471 // have valid types and not error
472 // FIXME(matthewjasper) We shouldn't need to use `track_errors`.
473 tcx.sess.track_errors(|| {
474 tcx.sess.time("type_collecting", || {
475 for &module in tcx.hir().krate().modules.keys() {
476 tcx.ensure().collect_mod_item_types(module);
481 if tcx.features().rustc_attrs {
482 tcx.sess.track_errors(|| {
483 tcx.sess.time("outlives_testing", || outlives::test::test_inferred_outlives(tcx));
487 tcx.sess.track_errors(|| {
488 tcx.sess.time("impl_wf_inference", || impl_wf_check::impl_wf_check(tcx));
491 tcx.sess.track_errors(|| {
492 tcx.sess.time("coherence_checking", || coherence::check_coherence(tcx));
495 if tcx.features().rustc_attrs {
496 tcx.sess.track_errors(|| {
497 tcx.sess.time("variance_testing", || variance::test::test_variance(tcx));
501 tcx.sess.track_errors(|| {
502 tcx.sess.time("wf_checking", || check::check_wf_new(tcx));
505 // NOTE: This is copy/pasted in librustdoc/core.rs and should be kept in sync.
506 tcx.sess.time("item_types_checking", || {
507 for &module in tcx.hir().krate().modules.keys() {
508 tcx.ensure().check_mod_item_types(module);
512 tcx.sess.time("item_bodies_checking", || tcx.typeck_item_bodies(()));
514 check_unused::check_crate(tcx);
515 check_for_entry_fn(tcx);
517 if tcx.sess.err_count() == 0 { Ok(()) } else { Err(ErrorReported) }
520 /// A quasi-deprecated helper used in rustdoc and clippy to get
521 /// the type from a HIR node.
522 pub fn hir_ty_to_ty<'tcx>(tcx: TyCtxt<'tcx>, hir_ty: &hir::Ty<'_>) -> Ty<'tcx> {
523 // In case there are any projections, etc., find the "environment"
524 // def-ID that will be used to determine the traits/predicates in
525 // scope. This is derived from the enclosing item-like thing.
526 let env_node_id = tcx.hir().get_parent_item(hir_ty.hir_id);
527 let env_def_id = tcx.hir().local_def_id(env_node_id);
528 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id.to_def_id());
529 <dyn AstConv<'_>>::ast_ty_to_ty(&item_cx, hir_ty)
532 pub fn hir_trait_to_predicates<'tcx>(
534 hir_trait: &hir::TraitRef<'_>,
537 // In case there are any projections, etc., find the "environment"
538 // def-ID that will be used to determine the traits/predicates in
539 // scope. This is derived from the enclosing item-like thing.
540 let env_hir_id = tcx.hir().get_parent_item(hir_trait.hir_ref_id);
541 let env_def_id = tcx.hir().local_def_id(env_hir_id);
542 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id.to_def_id());
543 let mut bounds = Bounds::default();
544 let _ = <dyn AstConv<'_>>::instantiate_poly_trait_ref(
548 hir::Constness::NotConst,