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(array_value_iter)]
60 #![feature(bool_to_option)]
61 #![feature(box_syntax)]
62 #![feature(crate_visibility_modifier)]
63 #![feature(in_band_lifetimes)]
64 #![feature(is_sorted)]
66 #![feature(or_patterns)]
67 #![feature(try_blocks)]
68 #![feature(never_type)]
69 #![feature(slice_partition_dedup)]
70 #![feature(control_flow_enum)]
71 #![recursion_limit = "256"]
77 extern crate rustc_middle;
79 // These are used by Clippy.
81 pub mod expr_use_visitor;
88 mod constrained_generic_params;
91 mod mem_categorization;
93 mod structured_errors;
96 use rustc_errors::{struct_span_err, ErrorReported};
98 use rustc_hir::def_id::{LocalDefId, LOCAL_CRATE};
100 use rustc_infer::infer::{InferOk, TyCtxtInferExt};
101 use rustc_infer::traits::TraitEngineExt as _;
102 use rustc_middle::middle;
103 use rustc_middle::ty::query::Providers;
104 use rustc_middle::ty::{self, Ty, TyCtxt};
105 use rustc_middle::util;
106 use rustc_session::config::EntryFnType;
107 use rustc_span::{symbol::sym, Span, DUMMY_SP};
108 use rustc_target::spec::abi::Abi;
109 use rustc_trait_selection::traits::error_reporting::InferCtxtExt as _;
110 use rustc_trait_selection::traits::{
111 ObligationCause, ObligationCauseCode, TraitEngine, TraitEngineExt as _,
116 use astconv::AstConv;
119 fn require_c_abi_if_c_variadic(tcx: TyCtxt<'_>, decl: &hir::FnDecl<'_>, abi: Abi, span: Span) {
120 if decl.c_variadic && !(abi == Abi::C || abi == Abi::Cdecl) {
121 let mut err = struct_span_err!(
125 "C-variadic function must have C or cdecl calling convention"
127 err.span_label(span, "C-variadics require C or cdecl calling convention").emit();
131 fn require_same_types<'tcx>(
133 cause: &ObligationCause<'tcx>,
137 tcx.infer_ctxt().enter(|ref infcx| {
138 let param_env = ty::ParamEnv::empty();
139 let mut fulfill_cx = TraitEngine::new(infcx.tcx);
140 match infcx.at(&cause, param_env).eq(expected, actual) {
141 Ok(InferOk { obligations, .. }) => {
142 fulfill_cx.register_predicate_obligations(infcx, obligations);
145 infcx.report_mismatched_types(cause, expected, actual, err).emit();
150 match fulfill_cx.select_all_or_error(infcx) {
153 infcx.report_fulfillment_errors(&errors, None, false);
160 fn check_main_fn_ty(tcx: TyCtxt<'_>, main_def_id: LocalDefId) {
161 let main_id = tcx.hir().local_def_id_to_hir_id(main_def_id);
162 let main_span = tcx.def_span(main_def_id);
163 let main_t = tcx.type_of(main_def_id);
164 match main_t.kind() {
166 if let Some(Node::Item(it)) = tcx.hir().find(main_id) {
167 if let hir::ItemKind::Fn(ref sig, ref generics, _) = it.kind {
168 let mut error = false;
169 if !generics.params.is_empty() {
170 let msg = "`main` function is not allowed to have generic \
173 let label = "`main` cannot have generic parameters".to_string();
174 struct_span_err!(tcx.sess, generics.span, E0131, "{}", msg)
175 .span_label(generics.span, label)
179 if let Some(sp) = generics.where_clause.span() {
184 "`main` function is not allowed to have a `where` clause"
186 .span_label(sp, "`main` cannot have a `where` clause")
190 if let hir::IsAsync::Async = sig.header.asyncness {
191 let span = tcx.sess.source_map().guess_head_span(it.span);
196 "`main` function is not allowed to be `async`"
198 .span_label(span, "`main` function is not allowed to be `async`")
203 for attr in it.attrs {
204 if tcx.sess.check_name(attr, sym::track_caller) {
208 "`main` function is not allowed to be `#[track_caller]`",
212 "`main` function is not allowed to be `#[track_caller]`",
225 let actual = tcx.fn_sig(main_def_id);
226 let expected_return_type = if tcx.lang_items().termination().is_some() {
227 // we take the return type of the given main function, the real check is done
229 actual.output().skip_binder()
231 // standard () main return type
235 let se_ty = tcx.mk_fn_ptr(ty::Binder::bind(tcx.mk_fn_sig(
237 expected_return_type,
239 hir::Unsafety::Normal,
245 &ObligationCause::new(main_span, main_id, ObligationCauseCode::MainFunctionType),
247 tcx.mk_fn_ptr(actual),
251 span_bug!(main_span, "main has a non-function type: found `{}`", main_t);
256 fn check_start_fn_ty(tcx: TyCtxt<'_>, start_def_id: LocalDefId) {
257 let start_id = tcx.hir().local_def_id_to_hir_id(start_def_id);
258 let start_span = tcx.def_span(start_def_id);
259 let start_t = tcx.type_of(start_def_id);
260 match start_t.kind() {
262 if let Some(Node::Item(it)) = tcx.hir().find(start_id) {
263 if let hir::ItemKind::Fn(ref sig, ref generics, _) = it.kind {
264 let mut error = false;
265 if !generics.params.is_empty() {
270 "start function is not allowed to have type parameters"
272 .span_label(generics.span, "start function cannot have type parameters")
276 if let Some(sp) = generics.where_clause.span() {
281 "start function is not allowed to have a `where` clause"
283 .span_label(sp, "start function cannot have a `where` clause")
287 if let hir::IsAsync::Async = sig.header.asyncness {
288 let span = tcx.sess.source_map().guess_head_span(it.span);
293 "`start` is not allowed to be `async`"
295 .span_label(span, "`start` is not allowed to be `async`")
300 for attr in it.attrs {
301 if tcx.sess.check_name(attr, sym::track_caller) {
305 "`start` is not allowed to be `#[track_caller]`",
309 "`start` is not allowed to be `#[track_caller]`",
322 let se_ty = tcx.mk_fn_ptr(ty::Binder::dummy(tcx.mk_fn_sig(
323 [tcx.types.isize, tcx.mk_imm_ptr(tcx.mk_imm_ptr(tcx.types.u8))].iter().cloned(),
326 hir::Unsafety::Normal,
332 &ObligationCause::new(start_span, start_id, ObligationCauseCode::StartFunctionType),
334 tcx.mk_fn_ptr(tcx.fn_sig(start_def_id)),
338 span_bug!(start_span, "start has a non-function type: found `{}`", start_t);
343 fn check_for_entry_fn(tcx: TyCtxt<'_>) {
344 match tcx.entry_fn(LOCAL_CRATE) {
345 Some((def_id, EntryFnType::Main)) => check_main_fn_ty(tcx, def_id),
346 Some((def_id, EntryFnType::Start)) => check_start_fn_ty(tcx, def_id),
351 pub fn provide(providers: &mut Providers) {
352 collect::provide(providers);
353 coherence::provide(providers);
354 check::provide(providers);
355 variance::provide(providers);
356 outlives::provide(providers);
357 impl_wf_check::provide(providers);
360 pub fn check_crate(tcx: TyCtxt<'_>) -> Result<(), ErrorReported> {
361 let _prof_timer = tcx.sess.timer("type_check_crate");
363 // this ensures that later parts of type checking can assume that items
364 // have valid types and not error
365 // FIXME(matthewjasper) We shouldn't need to use `track_errors`.
366 tcx.sess.track_errors(|| {
367 tcx.sess.time("type_collecting", || {
368 for &module in tcx.hir().krate().modules.keys() {
369 tcx.ensure().collect_mod_item_types(tcx.hir().local_def_id(module));
374 if tcx.features().rustc_attrs {
375 tcx.sess.track_errors(|| {
376 tcx.sess.time("outlives_testing", || outlives::test::test_inferred_outlives(tcx));
380 tcx.sess.track_errors(|| {
381 tcx.sess.time("impl_wf_inference", || impl_wf_check::impl_wf_check(tcx));
384 tcx.sess.track_errors(|| {
385 tcx.sess.time("coherence_checking", || coherence::check_coherence(tcx));
388 if tcx.features().rustc_attrs {
389 tcx.sess.track_errors(|| {
390 tcx.sess.time("variance_testing", || variance::test::test_variance(tcx));
394 tcx.sess.track_errors(|| {
395 tcx.sess.time("wf_checking", || check::check_wf_new(tcx));
398 // NOTE: This is copy/pasted in librustdoc/core.rs and should be kept in sync.
399 tcx.sess.time("item_types_checking", || {
400 for &module in tcx.hir().krate().modules.keys() {
401 tcx.ensure().check_mod_item_types(tcx.hir().local_def_id(module));
405 tcx.sess.time("item_bodies_checking", || tcx.typeck_item_bodies(LOCAL_CRATE));
407 check_unused::check_crate(tcx);
408 check_for_entry_fn(tcx);
410 if tcx.sess.err_count() == 0 { Ok(()) } else { Err(ErrorReported) }
413 /// A quasi-deprecated helper used in rustdoc and clippy to get
414 /// the type from a HIR node.
415 pub fn hir_ty_to_ty<'tcx>(tcx: TyCtxt<'tcx>, hir_ty: &hir::Ty<'_>) -> Ty<'tcx> {
416 // In case there are any projections, etc., find the "environment"
417 // def-ID that will be used to determine the traits/predicates in
418 // scope. This is derived from the enclosing item-like thing.
419 let env_node_id = tcx.hir().get_parent_item(hir_ty.hir_id);
420 let env_def_id = tcx.hir().local_def_id(env_node_id);
421 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id.to_def_id());
423 astconv::AstConv::ast_ty_to_ty(&item_cx, hir_ty)
426 pub fn hir_trait_to_predicates<'tcx>(
428 hir_trait: &hir::TraitRef<'_>,
431 // In case there are any projections, etc., find the "environment"
432 // def-ID that will be used to determine the traits/predicates in
433 // scope. This is derived from the enclosing item-like thing.
434 let env_hir_id = tcx.hir().get_parent_item(hir_trait.hir_ref_id);
435 let env_def_id = tcx.hir().local_def_id(env_hir_id);
436 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id.to_def_id());
437 let mut bounds = Bounds::default();
438 let _ = AstConv::instantiate_poly_trait_ref_inner(
442 hir::Constness::NotConst,