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 #![feature(slice_patterns)]
68 #![feature(never_type)]
69 #![recursion_limit = "256"]
79 // This is used by Clippy.
80 pub mod expr_use_visitor;
87 mod constrained_generic_params;
89 mod mem_categorization;
92 mod structured_errors;
95 use rustc::hir::def_id::{DefId, LOCAL_CRATE};
96 use rustc::hir::{self, Node};
97 use rustc::infer::InferOk;
101 use rustc::session::config::EntryFnType;
102 use rustc::traits::{ObligationCause, ObligationCauseCode, TraitEngine, TraitEngineExt};
103 use rustc::ty::query::Providers;
104 use rustc::ty::subst::SubstsRef;
105 use rustc::ty::{self, Ty, TyCtxt};
107 use rustc::util::common::ErrorReported;
108 use rustc_target::spec::abi::Abi;
109 use syntax_pos::{Span, DUMMY_SP};
110 use util::common::time;
112 use rustc_error_codes::*;
116 use astconv::{AstConv, Bounds};
117 pub struct TypeAndSubsts<'tcx> {
118 substs: SubstsRef<'tcx>,
122 fn require_c_abi_if_c_variadic(tcx: TyCtxt<'_>, decl: &hir::FnDecl<'_>, abi: Abi, span: Span) {
123 if decl.c_variadic && !(abi == Abi::C || abi == Abi::Cdecl) {
124 let mut err = struct_span_err!(
128 "C-variadic function must have C or cdecl calling convention"
130 err.span_label(span, "C-variadics require C or cdecl calling convention").emit();
134 fn require_same_types<'tcx>(
136 cause: &ObligationCause<'tcx>,
140 tcx.infer_ctxt().enter(|ref infcx| {
141 let param_env = ty::ParamEnv::empty();
142 let mut fulfill_cx = TraitEngine::new(infcx.tcx);
143 match infcx.at(&cause, param_env).eq(expected, actual) {
144 Ok(InferOk { obligations, .. }) => {
145 fulfill_cx.register_predicate_obligations(infcx, obligations);
148 infcx.report_mismatched_types(cause, expected, actual, err).emit();
153 match fulfill_cx.select_all_or_error(infcx) {
156 infcx.report_fulfillment_errors(&errors, None, false);
163 fn check_main_fn_ty(tcx: TyCtxt<'_>, main_def_id: DefId) {
164 let main_id = tcx.hir().as_local_hir_id(main_def_id).unwrap();
165 let main_span = tcx.def_span(main_def_id);
166 let main_t = tcx.type_of(main_def_id);
169 if let Some(Node::Item(it)) = tcx.hir().find(main_id) {
170 if let hir::ItemKind::Fn(.., ref generics, _) = it.kind {
171 let mut error = false;
172 if !generics.params.is_empty() {
173 let msg = "`main` function is not allowed to have generic \
176 let label = "`main` cannot have generic parameters".to_string();
177 struct_span_err!(tcx.sess, generics.span, E0131, "{}", msg)
178 .span_label(generics.span, label)
182 if let Some(sp) = generics.where_clause.span() {
187 "`main` function is not allowed to have a `where` clause"
189 .span_label(sp, "`main` cannot have a `where` clause")
199 let actual = tcx.fn_sig(main_def_id);
200 let expected_return_type = if tcx.lang_items().termination().is_some() {
201 // we take the return type of the given main function, the real check is done
203 actual.output().skip_binder()
205 // standard () main return type
209 let se_ty = tcx.mk_fn_ptr(ty::Binder::bind(tcx.mk_fn_sig(
211 expected_return_type,
213 hir::Unsafety::Normal,
219 &ObligationCause::new(main_span, main_id, ObligationCauseCode::MainFunctionType),
221 tcx.mk_fn_ptr(actual),
225 span_bug!(main_span, "main has a non-function type: found `{}`", main_t);
230 fn check_start_fn_ty(tcx: TyCtxt<'_>, start_def_id: DefId) {
231 let start_id = tcx.hir().as_local_hir_id(start_def_id).unwrap();
232 let start_span = tcx.def_span(start_def_id);
233 let start_t = tcx.type_of(start_def_id);
236 if let Some(Node::Item(it)) = tcx.hir().find(start_id) {
237 if let hir::ItemKind::Fn(.., ref generics, _) = it.kind {
238 let mut error = false;
239 if !generics.params.is_empty() {
244 "start function is not allowed to have type parameters"
246 .span_label(generics.span, "start function cannot have type parameters")
250 if let Some(sp) = generics.where_clause.span() {
255 "start function is not allowed to have a `where` clause"
257 .span_label(sp, "start function cannot have a `where` clause")
267 let se_ty = tcx.mk_fn_ptr(ty::Binder::bind(tcx.mk_fn_sig(
268 [tcx.types.isize, tcx.mk_imm_ptr(tcx.mk_imm_ptr(tcx.types.u8))].iter().cloned(),
271 hir::Unsafety::Normal,
277 &ObligationCause::new(start_span, start_id, ObligationCauseCode::StartFunctionType),
279 tcx.mk_fn_ptr(tcx.fn_sig(start_def_id)),
283 span_bug!(start_span, "start has a non-function type: found `{}`", start_t);
288 fn check_for_entry_fn(tcx: TyCtxt<'_>) {
289 match tcx.entry_fn(LOCAL_CRATE) {
290 Some((def_id, EntryFnType::Main)) => check_main_fn_ty(tcx, def_id),
291 Some((def_id, EntryFnType::Start)) => check_start_fn_ty(tcx, def_id),
296 pub fn provide(providers: &mut Providers<'_>) {
297 collect::provide(providers);
298 coherence::provide(providers);
299 check::provide(providers);
300 variance::provide(providers);
301 outlives::provide(providers);
302 impl_wf_check::provide(providers);
305 pub fn check_crate(tcx: TyCtxt<'_>) -> Result<(), ErrorReported> {
306 let _prof_timer = tcx.prof.generic_activity("type_check_crate");
308 // this ensures that later parts of type checking can assume that items
309 // have valid types and not error
310 // FIXME(matthewjasper) We shouldn't need to do this.
311 tcx.sess.track_errors(|| {
312 time(tcx.sess, "type collecting", || {
313 for &module in tcx.hir().krate().modules.keys() {
314 tcx.ensure().collect_mod_item_types(tcx.hir().local_def_id(module));
319 if tcx.features().rustc_attrs {
320 tcx.sess.track_errors(|| {
321 time(tcx.sess, "outlives testing", || outlives::test::test_inferred_outlives(tcx));
325 tcx.sess.track_errors(|| {
326 time(tcx.sess, "impl wf inference", || impl_wf_check::impl_wf_check(tcx));
329 tcx.sess.track_errors(|| {
330 time(tcx.sess, "coherence checking", || coherence::check_coherence(tcx));
333 if tcx.features().rustc_attrs {
334 tcx.sess.track_errors(|| {
335 time(tcx.sess, "variance testing", || variance::test::test_variance(tcx));
339 tcx.sess.track_errors(|| {
340 time(tcx.sess, "wf checking", || check::check_wf_new(tcx));
343 time(tcx.sess, "item-types checking", || {
344 for &module in tcx.hir().krate().modules.keys() {
345 tcx.ensure().check_mod_item_types(tcx.hir().local_def_id(module));
349 time(tcx.sess, "item-bodies checking", || tcx.typeck_item_bodies(LOCAL_CRATE));
351 check_unused::check_crate(tcx);
352 check_for_entry_fn(tcx);
354 if tcx.sess.err_count() == 0 { Ok(()) } else { Err(ErrorReported) }
357 /// A quasi-deprecated helper used in rustdoc and clippy to get
358 /// the type from a HIR node.
359 pub fn hir_ty_to_ty<'tcx>(tcx: TyCtxt<'tcx>, hir_ty: &hir::Ty<'_>) -> Ty<'tcx> {
360 // In case there are any projections, etc., find the "environment"
361 // def-ID that will be used to determine the traits/predicates in
362 // scope. This is derived from the enclosing item-like thing.
363 let env_node_id = tcx.hir().get_parent_item(hir_ty.hir_id);
364 let env_def_id = tcx.hir().local_def_id(env_node_id);
365 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id);
367 astconv::AstConv::ast_ty_to_ty(&item_cx, hir_ty)
370 pub fn hir_trait_to_predicates<'tcx>(
372 hir_trait: &hir::TraitRef<'_>,
374 // In case there are any projections, etc., find the "environment"
375 // def-ID that will be used to determine the traits/predicates in
376 // scope. This is derived from the enclosing item-like thing.
377 let env_hir_id = tcx.hir().get_parent_item(hir_trait.hir_ref_id);
378 let env_def_id = tcx.hir().local_def_id(env_hir_id);
379 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id);
380 let mut bounds = Bounds::default();
381 let _ = AstConv::instantiate_poly_trait_ref_inner(