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/")]
59 #![allow(non_camel_case_types)]
60 #![feature(bool_to_option)]
61 #![feature(box_syntax)]
62 #![feature(crate_visibility_modifier)]
63 #![feature(in_band_lifetimes)]
65 #![feature(or_patterns)]
66 #![feature(try_blocks)]
67 #![feature(never_type)]
68 #![feature(slice_partition_dedup)]
69 #![recursion_limit = "256"]
75 extern crate rustc_middle;
77 // This is used by Clippy.
78 pub mod expr_use_visitor;
85 mod constrained_generic_params;
87 mod mem_categorization;
89 mod structured_errors;
92 use rustc_errors::{struct_span_err, ErrorReported};
94 use rustc_hir::def_id::{DefId, LOCAL_CRATE};
96 use rustc_infer::infer::{InferOk, TyCtxtInferExt};
97 use rustc_infer::traits::TraitEngineExt as _;
98 use rustc_middle::middle;
99 use rustc_middle::ty::query::Providers;
100 use rustc_middle::ty::subst::SubstsRef;
101 use rustc_middle::ty::{self, Ty, TyCtxt};
102 use rustc_middle::util;
103 use rustc_session::config::EntryFnType;
104 use rustc_span::{Span, DUMMY_SP};
105 use rustc_target::spec::abi::Abi;
106 use rustc_trait_selection::traits::error_reporting::InferCtxtExt as _;
107 use rustc_trait_selection::traits::{
108 ObligationCause, ObligationCauseCode, TraitEngine, TraitEngineExt as _,
113 use astconv::{AstConv, Bounds};
114 pub struct TypeAndSubsts<'tcx> {
115 substs: SubstsRef<'tcx>,
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: DefId) {
161 let main_id = tcx.hir().as_local_hir_id(main_def_id).unwrap();
162 let main_span = tcx.def_span(main_def_id);
163 let main_t = tcx.type_of(main_def_id);
166 if let Some(Node::Item(it)) = tcx.hir().find(main_id) {
167 if let hir::ItemKind::Fn(.., 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")
196 let actual = tcx.fn_sig(main_def_id);
197 let expected_return_type = if tcx.lang_items().termination().is_some() {
198 // we take the return type of the given main function, the real check is done
200 actual.output().skip_binder()
202 // standard () main return type
206 let se_ty = tcx.mk_fn_ptr(ty::Binder::bind(tcx.mk_fn_sig(
208 expected_return_type,
210 hir::Unsafety::Normal,
216 &ObligationCause::new(main_span, main_id, ObligationCauseCode::MainFunctionType),
218 tcx.mk_fn_ptr(actual),
222 span_bug!(main_span, "main has a non-function type: found `{}`", main_t);
227 fn check_start_fn_ty(tcx: TyCtxt<'_>, start_def_id: DefId) {
228 let start_id = tcx.hir().as_local_hir_id(start_def_id).unwrap();
229 let start_span = tcx.def_span(start_def_id);
230 let start_t = tcx.type_of(start_def_id);
233 if let Some(Node::Item(it)) = tcx.hir().find(start_id) {
234 if let hir::ItemKind::Fn(.., ref generics, _) = it.kind {
235 let mut error = false;
236 if !generics.params.is_empty() {
241 "start function is not allowed to have type parameters"
243 .span_label(generics.span, "start function cannot have type parameters")
247 if let Some(sp) = generics.where_clause.span() {
252 "start function is not allowed to have a `where` clause"
254 .span_label(sp, "start function cannot have a `where` clause")
264 let se_ty = tcx.mk_fn_ptr(ty::Binder::bind(tcx.mk_fn_sig(
265 [tcx.types.isize, tcx.mk_imm_ptr(tcx.mk_imm_ptr(tcx.types.u8))].iter().cloned(),
268 hir::Unsafety::Normal,
274 &ObligationCause::new(start_span, start_id, ObligationCauseCode::StartFunctionType),
276 tcx.mk_fn_ptr(tcx.fn_sig(start_def_id)),
280 span_bug!(start_span, "start has a non-function type: found `{}`", start_t);
285 fn check_for_entry_fn(tcx: TyCtxt<'_>) {
286 match tcx.entry_fn(LOCAL_CRATE) {
287 Some((def_id, EntryFnType::Main)) => check_main_fn_ty(tcx, def_id),
288 Some((def_id, EntryFnType::Start)) => check_start_fn_ty(tcx, def_id),
293 pub fn provide(providers: &mut Providers<'_>) {
294 collect::provide(providers);
295 coherence::provide(providers);
296 check::provide(providers);
297 variance::provide(providers);
298 outlives::provide(providers);
299 impl_wf_check::provide(providers);
302 pub fn check_crate(tcx: TyCtxt<'_>) -> Result<(), ErrorReported> {
303 let _prof_timer = tcx.sess.timer("type_check_crate");
305 // this ensures that later parts of type checking can assume that items
306 // have valid types and not error
307 // FIXME(matthewjasper) We shouldn't need to do this.
308 tcx.sess.track_errors(|| {
309 tcx.sess.time("type_collecting", || {
310 for &module in tcx.hir().krate().modules.keys() {
311 tcx.ensure().collect_mod_item_types(tcx.hir().local_def_id(module));
316 if tcx.features().rustc_attrs {
317 tcx.sess.track_errors(|| {
318 tcx.sess.time("outlives_testing", || outlives::test::test_inferred_outlives(tcx));
322 tcx.sess.track_errors(|| {
323 tcx.sess.time("impl_wf_inference", || impl_wf_check::impl_wf_check(tcx));
326 tcx.sess.track_errors(|| {
327 tcx.sess.time("coherence_checking", || coherence::check_coherence(tcx));
330 if tcx.features().rustc_attrs {
331 tcx.sess.track_errors(|| {
332 tcx.sess.time("variance_testing", || variance::test::test_variance(tcx));
336 tcx.sess.track_errors(|| {
337 tcx.sess.time("wf_checking", || check::check_wf_new(tcx));
340 tcx.sess.time("item_types_checking", || {
341 for &module in tcx.hir().krate().modules.keys() {
342 tcx.ensure().check_mod_item_types(tcx.hir().local_def_id(module));
346 tcx.sess.time("item_bodies_checking", || tcx.typeck_item_bodies(LOCAL_CRATE));
348 check_unused::check_crate(tcx);
349 check_for_entry_fn(tcx);
351 if tcx.sess.err_count() == 0 { Ok(()) } else { Err(ErrorReported) }
354 /// A quasi-deprecated helper used in rustdoc and clippy to get
355 /// the type from a HIR node.
356 pub fn hir_ty_to_ty<'tcx>(tcx: TyCtxt<'tcx>, hir_ty: &hir::Ty<'_>) -> Ty<'tcx> {
357 // In case there are any projections, etc., find the "environment"
358 // def-ID that will be used to determine the traits/predicates in
359 // scope. This is derived from the enclosing item-like thing.
360 let env_node_id = tcx.hir().get_parent_item(hir_ty.hir_id);
361 let env_def_id = tcx.hir().local_def_id(env_node_id);
362 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id);
364 astconv::AstConv::ast_ty_to_ty(&item_cx, hir_ty)
367 pub fn hir_trait_to_predicates<'tcx>(
369 hir_trait: &hir::TraitRef<'_>,
371 // In case there are any projections, etc., find the "environment"
372 // def-ID that will be used to determine the traits/predicates in
373 // scope. This is derived from the enclosing item-like thing.
374 let env_hir_id = tcx.hir().get_parent_item(hir_trait.hir_ref_id);
375 let env_def_id = tcx.hir().local_def_id(env_hir_id);
376 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id);
377 let mut bounds = Bounds::default();
378 let _ = AstConv::instantiate_poly_trait_ref_inner(
382 hir::Constness::NotConst,