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(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;
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::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 let generics_param_span =
192 if !generics.params.is_empty() { Some(generics.span) } else { None };
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 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 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
221 match tcx.hir().find(hir_id) {
222 Some(Node::Item(hir::Item { span: item_span, .. })) => {
223 Some(tcx.sess.source_map().guess_head_span(*item_span))
226 span_bug!(tcx.def_span(def_id), "main has a non-function type");
231 fn main_fn_return_type_span(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Span> {
232 if !def_id.is_local() {
235 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
236 match tcx.hir().find(hir_id) {
237 Some(Node::Item(hir::Item { kind: hir::ItemKind::Fn(ref fn_sig, _, _), .. })) => {
238 Some(fn_sig.decl.output.span())
241 span_bug!(tcx.def_span(def_id), "main has a non-function type");
246 let mut error = false;
247 let main_diagnostics_hir_id = main_fn_diagnostics_hir_id(tcx, main_def_id, main_span);
248 let main_fn_generics = tcx.generics_of(main_def_id);
249 let main_fn_predicates = tcx.predicates_of(main_def_id);
250 if main_fn_generics.count() != 0 || !main_fnsig.bound_vars().is_empty() {
251 let generics_param_span = main_fn_generics_params_span(tcx, main_def_id);
252 let msg = "`main` function is not allowed to have generic \
255 struct_span_err!(tcx.sess, generics_param_span.unwrap_or(main_span), E0131, "{}", msg);
256 if let Some(generics_param_span) = generics_param_span {
257 let label = "`main` cannot have generic parameters".to_string();
258 diag.span_label(generics_param_span, label);
262 } else if !main_fn_predicates.predicates.is_empty() {
263 // generics may bring in implicit predicates, so we skip this check if generics is present.
264 let generics_where_clauses_span = main_fn_where_clauses_span(tcx, main_def_id);
265 let mut diag = struct_span_err!(
267 generics_where_clauses_span.unwrap_or(main_span),
269 "`main` function is not allowed to have a `where` clause"
271 if let Some(generics_where_clauses_span) = generics_where_clauses_span {
272 diag.span_label(generics_where_clauses_span, "`main` cannot have a `where` clause");
278 let main_asyncness = tcx.asyncness(main_def_id);
279 if let hir::IsAsync::Async = main_asyncness {
280 let mut diag = struct_span_err!(
284 "`main` function is not allowed to be `async`"
286 let asyncness_span = main_fn_asyncness_span(tcx, main_def_id);
287 if let Some(asyncness_span) = asyncness_span {
288 diag.span_label(asyncness_span, "`main` function is not allowed to be `async`");
294 for attr in tcx.get_attrs(main_def_id) {
295 if tcx.sess.check_name(attr, sym::track_caller) {
299 "`main` function is not allowed to be `#[track_caller]`",
301 .span_label(main_span, "`main` function is not allowed to be `#[track_caller]`")
311 let expected_return_type;
312 if let Some(term_id) = tcx.lang_items().termination() {
313 let return_ty = main_fnsig.output();
314 let return_ty_span = main_fn_return_type_span(tcx, main_def_id).unwrap_or(main_span);
315 if !return_ty.bound_vars().is_empty() {
316 let msg = "`main` function return type is not allowed to have generic \
319 struct_span_err!(tcx.sess, return_ty_span, E0131, "{}", msg).emit();
322 let return_ty = return_ty.skip_binder();
323 tcx.infer_ctxt().enter(|infcx| {
324 let cause = traits::ObligationCause::new(
326 main_diagnostics_hir_id,
327 ObligationCauseCode::MainFunctionType,
329 let mut fulfillment_cx = traits::FulfillmentContext::new();
330 fulfillment_cx.register_bound(&infcx, ty::ParamEnv::empty(), return_ty, term_id, cause);
331 if let Err(err) = fulfillment_cx.select_all_or_error(&infcx) {
332 infcx.report_fulfillment_errors(&err, None, false);
336 // now we can take the return type of the given main function
337 expected_return_type = main_fnsig.output();
339 // standard () main return type
340 expected_return_type = ty::Binder::dummy(tcx.mk_unit());
347 let se_ty = tcx.mk_fn_ptr(expected_return_type.map_bound(|expected_return_type| {
348 tcx.mk_fn_sig(iter::empty(), expected_return_type, false, hir::Unsafety::Normal, Abi::Rust)
353 &ObligationCause::new(
355 main_diagnostics_hir_id,
356 ObligationCauseCode::MainFunctionType,
359 tcx.mk_fn_ptr(main_fnsig),
362 fn check_start_fn_ty(tcx: TyCtxt<'_>, start_def_id: DefId) {
363 let start_def_id = start_def_id.expect_local();
364 let start_id = tcx.hir().local_def_id_to_hir_id(start_def_id);
365 let start_span = tcx.def_span(start_def_id);
366 let start_t = tcx.type_of(start_def_id);
367 match start_t.kind() {
369 if let Some(Node::Item(it)) = tcx.hir().find(start_id) {
370 if let hir::ItemKind::Fn(ref sig, ref generics, _) = it.kind {
371 let mut error = false;
372 if !generics.params.is_empty() {
377 "start function is not allowed to have type parameters"
379 .span_label(generics.span, "start function cannot have type parameters")
383 if let Some(sp) = generics.where_clause.span() {
388 "start function is not allowed to have a `where` clause"
390 .span_label(sp, "start function cannot have a `where` clause")
394 if let hir::IsAsync::Async = sig.header.asyncness {
395 let span = tcx.sess.source_map().guess_head_span(it.span);
400 "`start` is not allowed to be `async`"
402 .span_label(span, "`start` is not allowed to be `async`")
407 let attrs = tcx.hir().attrs(start_id);
409 if tcx.sess.check_name(attr, sym::track_caller) {
413 "`start` is not allowed to be `#[track_caller]`",
417 "`start` is not allowed to be `#[track_caller]`",
430 let se_ty = tcx.mk_fn_ptr(ty::Binder::dummy(tcx.mk_fn_sig(
431 [tcx.types.isize, tcx.mk_imm_ptr(tcx.mk_imm_ptr(tcx.types.u8))].iter().cloned(),
434 hir::Unsafety::Normal,
440 &ObligationCause::new(start_span, start_id, ObligationCauseCode::StartFunctionType),
442 tcx.mk_fn_ptr(tcx.fn_sig(start_def_id)),
446 span_bug!(start_span, "start has a non-function type: found `{}`", start_t);
451 fn check_for_entry_fn(tcx: TyCtxt<'_>) {
452 match tcx.entry_fn(()) {
453 Some((def_id, EntryFnType::Main)) => check_main_fn_ty(tcx, def_id),
454 Some((def_id, EntryFnType::Start)) => check_start_fn_ty(tcx, def_id),
459 pub fn provide(providers: &mut Providers) {
460 collect::provide(providers);
461 coherence::provide(providers);
462 check::provide(providers);
463 variance::provide(providers);
464 outlives::provide(providers);
465 impl_wf_check::provide(providers);
466 hir_wf_check::provide(providers);
469 pub fn check_crate(tcx: TyCtxt<'_>) -> Result<(), ErrorReported> {
470 let _prof_timer = tcx.sess.timer("type_check_crate");
472 // this ensures that later parts of type checking can assume that items
473 // have valid types and not error
474 // FIXME(matthewjasper) We shouldn't need to use `track_errors`.
475 tcx.sess.track_errors(|| {
476 tcx.sess.time("type_collecting", || {
477 for &module in tcx.hir().krate().modules.keys() {
478 tcx.ensure().collect_mod_item_types(module);
483 if tcx.features().rustc_attrs {
484 tcx.sess.track_errors(|| {
485 tcx.sess.time("outlives_testing", || outlives::test::test_inferred_outlives(tcx));
489 tcx.sess.track_errors(|| {
490 tcx.sess.time("impl_wf_inference", || impl_wf_check::impl_wf_check(tcx));
493 tcx.sess.track_errors(|| {
494 tcx.sess.time("coherence_checking", || coherence::check_coherence(tcx));
497 if tcx.features().rustc_attrs {
498 tcx.sess.track_errors(|| {
499 tcx.sess.time("variance_testing", || variance::test::test_variance(tcx));
503 tcx.sess.track_errors(|| {
504 tcx.sess.time("wf_checking", || check::check_wf_new(tcx));
507 // NOTE: This is copy/pasted in librustdoc/core.rs and should be kept in sync.
508 tcx.sess.time("item_types_checking", || {
509 for &module in tcx.hir().krate().modules.keys() {
510 tcx.ensure().check_mod_item_types(module);
514 tcx.sess.time("item_bodies_checking", || tcx.typeck_item_bodies(()));
516 check_unused::check_crate(tcx);
517 check_for_entry_fn(tcx);
519 if tcx.sess.err_count() == 0 { Ok(()) } else { Err(ErrorReported) }
522 /// A quasi-deprecated helper used in rustdoc and clippy to get
523 /// the type from a HIR node.
524 pub fn hir_ty_to_ty<'tcx>(tcx: TyCtxt<'tcx>, hir_ty: &hir::Ty<'_>) -> Ty<'tcx> {
525 // In case there are any projections, etc., find the "environment"
526 // def-ID that will be used to determine the traits/predicates in
527 // scope. This is derived from the enclosing item-like thing.
528 let env_node_id = tcx.hir().get_parent_item(hir_ty.hir_id);
529 let env_def_id = tcx.hir().local_def_id(env_node_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_hir_id = tcx.hir().get_parent_item(hir_trait.hir_ref_id);
543 let env_def_id = tcx.hir().local_def_id(env_hir_id);
544 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id.to_def_id());
545 let mut bounds = Bounds::default();
546 let _ = <dyn AstConv<'_>>::instantiate_poly_trait_ref(
550 hir::Constness::NotConst,