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(try_blocks)]
69 #![feature(never_type)]
70 #![recursion_limit = "256"]
80 // This is used by Clippy.
81 pub mod expr_use_visitor;
88 mod constrained_generic_params;
90 mod mem_categorization;
93 mod structured_errors;
96 use rustc::hir::def_id::{DefId, LOCAL_CRATE};
97 use rustc::hir::{self, Node};
98 use rustc::infer::InferOk;
102 use rustc::session::config::EntryFnType;
103 use rustc::traits::{ObligationCause, ObligationCauseCode, TraitEngine, TraitEngineExt};
104 use rustc::ty::query::Providers;
105 use rustc::ty::subst::SubstsRef;
106 use rustc::ty::{self, Ty, TyCtxt};
108 use rustc::util::common::ErrorReported;
109 use rustc_span::{Span, DUMMY_SP};
110 use rustc_target::spec::abi::Abi;
111 use util::common::time;
113 use rustc_error_codes::*;
117 use astconv::{AstConv, Bounds};
118 pub struct TypeAndSubsts<'tcx> {
119 substs: SubstsRef<'tcx>,
123 fn require_c_abi_if_c_variadic(tcx: TyCtxt<'_>, decl: &hir::FnDecl<'_>, abi: Abi, span: Span) {
124 if decl.c_variadic && !(abi == Abi::C || abi == Abi::Cdecl) {
125 let mut err = struct_span_err!(
129 "C-variadic function must have C or cdecl calling convention"
131 err.span_label(span, "C-variadics require C or cdecl calling convention").emit();
135 fn require_same_types<'tcx>(
137 cause: &ObligationCause<'tcx>,
141 tcx.infer_ctxt().enter(|ref infcx| {
142 let param_env = ty::ParamEnv::empty();
143 let mut fulfill_cx = TraitEngine::new(infcx.tcx);
144 match infcx.at(&cause, param_env).eq(expected, actual) {
145 Ok(InferOk { obligations, .. }) => {
146 fulfill_cx.register_predicate_obligations(infcx, obligations);
149 infcx.report_mismatched_types(cause, expected, actual, err).emit();
154 match fulfill_cx.select_all_or_error(infcx) {
157 infcx.report_fulfillment_errors(&errors, None, false);
164 fn check_main_fn_ty(tcx: TyCtxt<'_>, main_def_id: DefId) {
165 let main_id = tcx.hir().as_local_hir_id(main_def_id).unwrap();
166 let main_span = tcx.def_span(main_def_id);
167 let main_t = tcx.type_of(main_def_id);
170 if let Some(Node::Item(it)) = tcx.hir().find(main_id) {
171 if let hir::ItemKind::Fn(.., ref generics, _) = it.kind {
172 let mut error = false;
173 if !generics.params.is_empty() {
174 let msg = "`main` function is not allowed to have generic \
177 let label = "`main` cannot have generic parameters".to_string();
178 struct_span_err!(tcx.sess, generics.span, E0131, "{}", msg)
179 .span_label(generics.span, label)
183 if let Some(sp) = generics.where_clause.span() {
188 "`main` function is not allowed to have a `where` clause"
190 .span_label(sp, "`main` cannot have a `where` clause")
200 let actual = tcx.fn_sig(main_def_id);
201 let expected_return_type = if tcx.lang_items().termination().is_some() {
202 // we take the return type of the given main function, the real check is done
204 actual.output().skip_binder()
206 // standard () main return type
210 let se_ty = tcx.mk_fn_ptr(ty::Binder::bind(tcx.mk_fn_sig(
212 expected_return_type,
214 hir::Unsafety::Normal,
220 &ObligationCause::new(main_span, main_id, ObligationCauseCode::MainFunctionType),
222 tcx.mk_fn_ptr(actual),
226 span_bug!(main_span, "main has a non-function type: found `{}`", main_t);
231 fn check_start_fn_ty(tcx: TyCtxt<'_>, start_def_id: DefId) {
232 let start_id = tcx.hir().as_local_hir_id(start_def_id).unwrap();
233 let start_span = tcx.def_span(start_def_id);
234 let start_t = tcx.type_of(start_def_id);
237 if let Some(Node::Item(it)) = tcx.hir().find(start_id) {
238 if let hir::ItemKind::Fn(.., ref generics, _) = it.kind {
239 let mut error = false;
240 if !generics.params.is_empty() {
245 "start function is not allowed to have type parameters"
247 .span_label(generics.span, "start function cannot have type parameters")
251 if let Some(sp) = generics.where_clause.span() {
256 "start function is not allowed to have a `where` clause"
258 .span_label(sp, "start function cannot have a `where` clause")
268 let se_ty = tcx.mk_fn_ptr(ty::Binder::bind(tcx.mk_fn_sig(
269 [tcx.types.isize, tcx.mk_imm_ptr(tcx.mk_imm_ptr(tcx.types.u8))].iter().cloned(),
272 hir::Unsafety::Normal,
278 &ObligationCause::new(start_span, start_id, ObligationCauseCode::StartFunctionType),
280 tcx.mk_fn_ptr(tcx.fn_sig(start_def_id)),
284 span_bug!(start_span, "start has a non-function type: found `{}`", start_t);
289 fn check_for_entry_fn(tcx: TyCtxt<'_>) {
290 match tcx.entry_fn(LOCAL_CRATE) {
291 Some((def_id, EntryFnType::Main)) => check_main_fn_ty(tcx, def_id),
292 Some((def_id, EntryFnType::Start)) => check_start_fn_ty(tcx, def_id),
297 pub fn provide(providers: &mut Providers<'_>) {
298 collect::provide(providers);
299 coherence::provide(providers);
300 check::provide(providers);
301 variance::provide(providers);
302 outlives::provide(providers);
303 impl_wf_check::provide(providers);
306 pub fn check_crate(tcx: TyCtxt<'_>) -> Result<(), ErrorReported> {
307 let _prof_timer = tcx.prof.generic_activity("type_check_crate");
309 // this ensures that later parts of type checking can assume that items
310 // have valid types and not error
311 // FIXME(matthewjasper) We shouldn't need to do this.
312 tcx.sess.track_errors(|| {
313 time(tcx.sess, "type collecting", || {
314 for &module in tcx.hir().krate().modules.keys() {
315 tcx.ensure().collect_mod_item_types(tcx.hir().local_def_id(module));
320 if tcx.features().rustc_attrs {
321 tcx.sess.track_errors(|| {
322 time(tcx.sess, "outlives testing", || outlives::test::test_inferred_outlives(tcx));
326 tcx.sess.track_errors(|| {
327 time(tcx.sess, "impl wf inference", || impl_wf_check::impl_wf_check(tcx));
330 tcx.sess.track_errors(|| {
331 time(tcx.sess, "coherence checking", || coherence::check_coherence(tcx));
334 if tcx.features().rustc_attrs {
335 tcx.sess.track_errors(|| {
336 time(tcx.sess, "variance testing", || variance::test::test_variance(tcx));
340 tcx.sess.track_errors(|| {
341 time(tcx.sess, "wf checking", || check::check_wf_new(tcx));
344 time(tcx.sess, "item-types checking", || {
345 for &module in tcx.hir().krate().modules.keys() {
346 tcx.ensure().check_mod_item_types(tcx.hir().local_def_id(module));
350 time(tcx.sess, "item-bodies checking", || tcx.typeck_item_bodies(LOCAL_CRATE));
352 check_unused::check_crate(tcx);
353 check_for_entry_fn(tcx);
355 if tcx.sess.err_count() == 0 { Ok(()) } else { Err(ErrorReported) }
358 /// A quasi-deprecated helper used in rustdoc and clippy to get
359 /// the type from a HIR node.
360 pub fn hir_ty_to_ty<'tcx>(tcx: TyCtxt<'tcx>, hir_ty: &hir::Ty<'_>) -> Ty<'tcx> {
361 // In case there are any projections, etc., find the "environment"
362 // def-ID that will be used to determine the traits/predicates in
363 // scope. This is derived from the enclosing item-like thing.
364 let env_node_id = tcx.hir().get_parent_item(hir_ty.hir_id);
365 let env_def_id = tcx.hir().local_def_id(env_node_id);
366 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id);
368 astconv::AstConv::ast_ty_to_ty(&item_cx, hir_ty)
371 pub fn hir_trait_to_predicates<'tcx>(
373 hir_trait: &hir::TraitRef<'_>,
375 // In case there are any projections, etc., find the "environment"
376 // def-ID that will be used to determine the traits/predicates in
377 // scope. This is derived from the enclosing item-like thing.
378 let env_hir_id = tcx.hir().get_parent_item(hir_trait.hir_ref_id);
379 let env_def_id = tcx.hir().local_def_id(env_hir_id);
380 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id);
381 let mut bounds = Bounds::default();
382 let _ = AstConv::instantiate_poly_trait_ref_inner(