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_patterns)]
62 #![feature(box_syntax)]
63 #![feature(crate_visibility_modifier)]
64 #![feature(exhaustive_patterns)]
65 #![feature(in_band_lifetimes)]
67 #![cfg_attr(bootstrap, feature(slice_patterns))]
68 #![feature(try_blocks)]
69 #![feature(never_type)]
70 #![recursion_limit = "256"]
78 // This is used by Clippy.
79 pub mod expr_use_visitor;
86 mod constrained_generic_params;
88 mod mem_categorization;
91 mod structured_errors;
94 use rustc::infer::InferOk;
98 use rustc::session::config::EntryFnType;
99 use rustc::traits::{ObligationCause, ObligationCauseCode, TraitEngine, TraitEngineExt};
100 use rustc::ty::query::Providers;
101 use rustc::ty::subst::SubstsRef;
102 use rustc::ty::{self, Ty, TyCtxt};
104 use rustc::util::common::ErrorReported;
105 use rustc_errors::struct_span_err;
106 use rustc_hir as hir;
107 use rustc_hir::def_id::{DefId, LOCAL_CRATE};
109 use rustc_span::{Span, DUMMY_SP};
110 use rustc_target::spec::abi::Abi;
114 use astconv::{AstConv, Bounds};
115 pub struct TypeAndSubsts<'tcx> {
116 substs: SubstsRef<'tcx>,
120 fn require_c_abi_if_c_variadic(tcx: TyCtxt<'_>, decl: &hir::FnDecl<'_>, abi: Abi, span: Span) {
121 if decl.c_variadic && !(abi == Abi::C || abi == Abi::Cdecl) {
122 let mut err = struct_span_err!(
126 "C-variadic function must have C or cdecl calling convention"
128 err.span_label(span, "C-variadics require C or cdecl calling convention").emit();
132 fn require_same_types<'tcx>(
134 cause: &ObligationCause<'tcx>,
138 tcx.infer_ctxt().enter(|ref infcx| {
139 let param_env = ty::ParamEnv::empty();
140 let mut fulfill_cx = TraitEngine::new(infcx.tcx);
141 match infcx.at(&cause, param_env).eq(expected, actual) {
142 Ok(InferOk { obligations, .. }) => {
143 fulfill_cx.register_predicate_obligations(infcx, obligations);
146 infcx.report_mismatched_types(cause, expected, actual, err).emit();
151 match fulfill_cx.select_all_or_error(infcx) {
154 infcx.report_fulfillment_errors(&errors, None, false);
161 fn check_main_fn_ty(tcx: TyCtxt<'_>, main_def_id: DefId) {
162 let main_id = tcx.hir().as_local_hir_id(main_def_id).unwrap();
163 let main_span = tcx.def_span(main_def_id);
164 let main_t = tcx.type_of(main_def_id);
167 if let Some(Node::Item(it)) = tcx.hir().find(main_id) {
168 if let hir::ItemKind::Fn(.., ref generics, _) = it.kind {
169 let mut error = false;
170 if !generics.params.is_empty() {
171 let msg = "`main` function is not allowed to have generic \
174 let label = "`main` cannot have generic parameters".to_string();
175 struct_span_err!(tcx.sess, generics.span, E0131, "{}", msg)
176 .span_label(generics.span, label)
180 if let Some(sp) = generics.where_clause.span() {
185 "`main` function is not allowed to have a `where` clause"
187 .span_label(sp, "`main` cannot have a `where` clause")
197 let actual = tcx.fn_sig(main_def_id);
198 let expected_return_type = if tcx.lang_items().termination().is_some() {
199 // we take the return type of the given main function, the real check is done
201 actual.output().skip_binder()
203 // standard () main return type
207 let se_ty = tcx.mk_fn_ptr(ty::Binder::bind(tcx.mk_fn_sig(
209 expected_return_type,
211 hir::Unsafety::Normal,
217 &ObligationCause::new(main_span, main_id, ObligationCauseCode::MainFunctionType),
219 tcx.mk_fn_ptr(actual),
223 span_bug!(main_span, "main has a non-function type: found `{}`", main_t);
228 fn check_start_fn_ty(tcx: TyCtxt<'_>, start_def_id: DefId) {
229 let start_id = tcx.hir().as_local_hir_id(start_def_id).unwrap();
230 let start_span = tcx.def_span(start_def_id);
231 let start_t = tcx.type_of(start_def_id);
234 if let Some(Node::Item(it)) = tcx.hir().find(start_id) {
235 if let hir::ItemKind::Fn(.., ref generics, _) = it.kind {
236 let mut error = false;
237 if !generics.params.is_empty() {
242 "start function is not allowed to have type parameters"
244 .span_label(generics.span, "start function cannot have type parameters")
248 if let Some(sp) = generics.where_clause.span() {
253 "start function is not allowed to have a `where` clause"
255 .span_label(sp, "start function cannot have a `where` clause")
265 let se_ty = tcx.mk_fn_ptr(ty::Binder::bind(tcx.mk_fn_sig(
266 [tcx.types.isize, tcx.mk_imm_ptr(tcx.mk_imm_ptr(tcx.types.u8))].iter().cloned(),
269 hir::Unsafety::Normal,
275 &ObligationCause::new(start_span, start_id, ObligationCauseCode::StartFunctionType),
277 tcx.mk_fn_ptr(tcx.fn_sig(start_def_id)),
281 span_bug!(start_span, "start has a non-function type: found `{}`", start_t);
286 fn check_for_entry_fn(tcx: TyCtxt<'_>) {
287 match tcx.entry_fn(LOCAL_CRATE) {
288 Some((def_id, EntryFnType::Main)) => check_main_fn_ty(tcx, def_id),
289 Some((def_id, EntryFnType::Start)) => check_start_fn_ty(tcx, def_id),
294 pub fn provide(providers: &mut Providers<'_>) {
295 collect::provide(providers);
296 coherence::provide(providers);
297 check::provide(providers);
298 variance::provide(providers);
299 outlives::provide(providers);
300 impl_wf_check::provide(providers);
303 pub fn check_crate(tcx: TyCtxt<'_>) -> Result<(), ErrorReported> {
304 let _prof_timer = tcx.sess.timer("type_check_crate");
306 // this ensures that later parts of type checking can assume that items
307 // have valid types and not error
308 // FIXME(matthewjasper) We shouldn't need to do this.
309 tcx.sess.track_errors(|| {
310 tcx.sess.time("type_collecting", || {
311 for &module in tcx.hir().krate().modules.keys() {
312 tcx.ensure().collect_mod_item_types(tcx.hir().local_def_id(module));
317 if tcx.features().rustc_attrs {
318 tcx.sess.track_errors(|| {
319 tcx.sess.time("outlives_testing", || outlives::test::test_inferred_outlives(tcx));
323 tcx.sess.track_errors(|| {
324 tcx.sess.time("impl_wf_inference", || impl_wf_check::impl_wf_check(tcx));
327 tcx.sess.track_errors(|| {
328 tcx.sess.time("coherence_checking", || coherence::check_coherence(tcx));
331 if tcx.features().rustc_attrs {
332 tcx.sess.track_errors(|| {
333 tcx.sess.time("variance_testing", || variance::test::test_variance(tcx));
337 tcx.sess.track_errors(|| {
338 tcx.sess.time("wf_checking", || check::check_wf_new(tcx));
341 tcx.sess.time("item_types_checking", || {
342 for &module in tcx.hir().krate().modules.keys() {
343 tcx.ensure().check_mod_item_types(tcx.hir().local_def_id(module));
347 tcx.sess.time("item_bodies_checking", || tcx.typeck_item_bodies(LOCAL_CRATE));
349 check_unused::check_crate(tcx);
350 check_for_entry_fn(tcx);
352 if tcx.sess.err_count() == 0 { Ok(()) } else { Err(ErrorReported) }
355 /// A quasi-deprecated helper used in rustdoc and clippy to get
356 /// the type from a HIR node.
357 pub fn hir_ty_to_ty<'tcx>(tcx: TyCtxt<'tcx>, hir_ty: &hir::Ty<'_>) -> Ty<'tcx> {
358 // In case there are any projections, etc., find the "environment"
359 // def-ID that will be used to determine the traits/predicates in
360 // scope. This is derived from the enclosing item-like thing.
361 let env_node_id = tcx.hir().get_parent_item(hir_ty.hir_id);
362 let env_def_id = tcx.hir().local_def_id(env_node_id);
363 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id);
365 astconv::AstConv::ast_ty_to_ty(&item_cx, hir_ty)
368 pub fn hir_trait_to_predicates<'tcx>(
370 hir_trait: &hir::TraitRef<'_>,
372 // In case there are any projections, etc., find the "environment"
373 // def-ID that will be used to determine the traits/predicates in
374 // scope. This is derived from the enclosing item-like thing.
375 let env_hir_id = tcx.hir().get_parent_item(hir_trait.hir_ref_id);
376 let env_def_id = tcx.hir().local_def_id(env_hir_id);
377 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id);
378 let mut bounds = Bounds::default();
379 let _ = AstConv::instantiate_poly_trait_ref_inner(
383 syntax::ast::Constness::NotConst,