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)]
67 #![feature(or_patterns)]
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::{LocalDefId, LOCAL_CRATE};
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 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: LocalDefId) {
167 let main_id = tcx.hir().local_def_id_to_hir_id(main_def_id);
168 let main_span = tcx.def_span(main_def_id);
169 let main_t = tcx.type_of(main_def_id);
170 match main_t.kind() {
172 if let Some(Node::Item(it)) = tcx.hir().find(main_id) {
173 if let hir::ItemKind::Fn(ref sig, ref generics, _) = it.kind {
174 let mut error = false;
175 if !generics.params.is_empty() {
176 let msg = "`main` function is not allowed to have generic \
179 let label = "`main` cannot have generic parameters".to_string();
180 struct_span_err!(tcx.sess, generics.span, E0131, "{}", msg)
181 .span_label(generics.span, label)
185 if let Some(sp) = generics.where_clause.span() {
190 "`main` function is not allowed to have a `where` clause"
192 .span_label(sp, "`main` cannot have a `where` clause")
196 if let hir::IsAsync::Async = sig.header.asyncness {
197 let span = tcx.sess.source_map().guess_head_span(it.span);
202 "`main` function is not allowed to be `async`"
204 .span_label(span, "`main` function is not allowed to be `async`")
209 let attrs = tcx.hir().attrs(main_id);
211 if tcx.sess.check_name(attr, sym::track_caller) {
215 "`main` function is not allowed to be `#[track_caller]`",
219 "`main` function is not allowed to be `#[track_caller]`",
232 let actual = tcx.fn_sig(main_def_id);
233 let expected_return_type = if tcx.lang_items().termination().is_some() {
234 // we take the return type of the given main function, the real check is done
238 // standard () main return type
239 ty::Binder::dummy(tcx.mk_unit())
242 let se_ty = tcx.mk_fn_ptr(expected_return_type.map_bound(|expected_return_type| {
245 expected_return_type,
247 hir::Unsafety::Normal,
254 &ObligationCause::new(main_span, main_id, ObligationCauseCode::MainFunctionType),
256 tcx.mk_fn_ptr(actual),
260 span_bug!(main_span, "main has a non-function type: found `{}`", main_t);
265 fn check_start_fn_ty(tcx: TyCtxt<'_>, start_def_id: LocalDefId) {
266 let start_id = tcx.hir().local_def_id_to_hir_id(start_def_id);
267 let start_span = tcx.def_span(start_def_id);
268 let start_t = tcx.type_of(start_def_id);
269 match start_t.kind() {
271 if let Some(Node::Item(it)) = tcx.hir().find(start_id) {
272 if let hir::ItemKind::Fn(ref sig, ref generics, _) = it.kind {
273 let mut error = false;
274 if !generics.params.is_empty() {
279 "start function is not allowed to have type parameters"
281 .span_label(generics.span, "start function cannot have type parameters")
285 if let Some(sp) = generics.where_clause.span() {
290 "start function is not allowed to have a `where` clause"
292 .span_label(sp, "start function cannot have a `where` clause")
296 if let hir::IsAsync::Async = sig.header.asyncness {
297 let span = tcx.sess.source_map().guess_head_span(it.span);
302 "`start` is not allowed to be `async`"
304 .span_label(span, "`start` is not allowed to be `async`")
309 let attrs = tcx.hir().attrs(start_id);
311 if tcx.sess.check_name(attr, sym::track_caller) {
315 "`start` is not allowed to be `#[track_caller]`",
319 "`start` is not allowed to be `#[track_caller]`",
332 let se_ty = tcx.mk_fn_ptr(ty::Binder::dummy(tcx.mk_fn_sig(
333 [tcx.types.isize, tcx.mk_imm_ptr(tcx.mk_imm_ptr(tcx.types.u8))].iter().cloned(),
336 hir::Unsafety::Normal,
342 &ObligationCause::new(start_span, start_id, ObligationCauseCode::StartFunctionType),
344 tcx.mk_fn_ptr(tcx.fn_sig(start_def_id)),
348 span_bug!(start_span, "start has a non-function type: found `{}`", start_t);
353 fn check_for_entry_fn(tcx: TyCtxt<'_>) {
354 match tcx.entry_fn(LOCAL_CRATE) {
355 Some((def_id, EntryFnType::Main)) => check_main_fn_ty(tcx, def_id),
356 Some((def_id, EntryFnType::Start)) => check_start_fn_ty(tcx, def_id),
361 pub fn provide(providers: &mut Providers) {
362 collect::provide(providers);
363 coherence::provide(providers);
364 check::provide(providers);
365 variance::provide(providers);
366 outlives::provide(providers);
367 impl_wf_check::provide(providers);
370 pub fn check_crate(tcx: TyCtxt<'_>) -> Result<(), ErrorReported> {
371 let _prof_timer = tcx.sess.timer("type_check_crate");
373 // this ensures that later parts of type checking can assume that items
374 // have valid types and not error
375 // FIXME(matthewjasper) We shouldn't need to use `track_errors`.
376 tcx.sess.track_errors(|| {
377 tcx.sess.time("type_collecting", || {
378 for &module in tcx.hir().krate().modules.keys() {
379 tcx.ensure().collect_mod_item_types(module);
384 if tcx.features().rustc_attrs {
385 tcx.sess.track_errors(|| {
386 tcx.sess.time("outlives_testing", || outlives::test::test_inferred_outlives(tcx));
390 tcx.sess.track_errors(|| {
391 tcx.sess.time("impl_wf_inference", || impl_wf_check::impl_wf_check(tcx));
394 tcx.sess.track_errors(|| {
395 tcx.sess.time("coherence_checking", || coherence::check_coherence(tcx));
398 if tcx.features().rustc_attrs {
399 tcx.sess.track_errors(|| {
400 tcx.sess.time("variance_testing", || variance::test::test_variance(tcx));
404 tcx.sess.track_errors(|| {
405 tcx.sess.time("wf_checking", || check::check_wf_new(tcx));
408 // NOTE: This is copy/pasted in librustdoc/core.rs and should be kept in sync.
409 tcx.sess.time("item_types_checking", || {
410 for &module in tcx.hir().krate().modules.keys() {
411 tcx.ensure().check_mod_item_types(module);
415 tcx.sess.time("item_bodies_checking", || tcx.typeck_item_bodies(LOCAL_CRATE));
417 check_unused::check_crate(tcx);
418 check_for_entry_fn(tcx);
420 if tcx.sess.err_count() == 0 { Ok(()) } else { Err(ErrorReported) }
423 /// A quasi-deprecated helper used in rustdoc and clippy to get
424 /// the type from a HIR node.
425 pub fn hir_ty_to_ty<'tcx>(tcx: TyCtxt<'tcx>, hir_ty: &hir::Ty<'_>) -> Ty<'tcx> {
426 // In case there are any projections, etc., find the "environment"
427 // def-ID that will be used to determine the traits/predicates in
428 // scope. This is derived from the enclosing item-like thing.
429 let env_node_id = tcx.hir().get_parent_item(hir_ty.hir_id);
430 let env_def_id = tcx.hir().local_def_id(env_node_id);
431 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id.to_def_id());
432 item_cx.to_ty(hir_ty)
435 pub fn hir_trait_to_predicates<'tcx>(
437 hir_trait: &hir::TraitRef<'_>,
440 // In case there are any projections, etc., find the "environment"
441 // def-ID that will be used to determine the traits/predicates in
442 // scope. This is derived from the enclosing item-like thing.
443 let env_hir_id = tcx.hir().get_parent_item(hir_trait.hir_ref_id);
444 let env_def_id = tcx.hir().local_def_id(env_hir_id);
445 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id.to_def_id());
446 let mut bounds = Bounds::default();
447 let _ = <dyn AstConv<'_>>::instantiate_poly_trait_ref_inner(
451 hir::Constness::NotConst,