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(try_blocks)]
66 #![feature(never_type)]
67 #![recursion_limit = "256"]
75 // This is used by Clippy.
76 pub mod expr_use_visitor;
83 mod constrained_generic_params;
85 mod mem_categorization;
88 mod structured_errors;
91 use rustc::infer::InferOk;
95 use rustc::session::config::EntryFnType;
96 use rustc::traits::{ObligationCause, ObligationCauseCode, TraitEngine, TraitEngineExt};
97 use rustc::ty::query::Providers;
98 use rustc::ty::subst::SubstsRef;
99 use rustc::ty::{self, Ty, TyCtxt};
101 use rustc::util::common::ErrorReported;
102 use rustc_errors::struct_span_err;
103 use rustc_hir as hir;
104 use rustc_hir::def_id::{DefId, LOCAL_CRATE};
106 use rustc_span::{Span, DUMMY_SP};
107 use rustc_target::spec::abi::Abi;
111 use astconv::{AstConv, Bounds};
112 pub struct TypeAndSubsts<'tcx> {
113 substs: SubstsRef<'tcx>,
117 fn require_c_abi_if_c_variadic(tcx: TyCtxt<'_>, decl: &hir::FnDecl<'_>, abi: Abi, span: Span) {
118 if decl.c_variadic && !(abi == Abi::C || abi == Abi::Cdecl) {
119 let mut err = struct_span_err!(
123 "C-variadic function must have C or cdecl calling convention"
125 err.span_label(span, "C-variadics require C or cdecl calling convention").emit();
129 fn require_same_types<'tcx>(
131 cause: &ObligationCause<'tcx>,
135 tcx.infer_ctxt().enter(|ref infcx| {
136 let param_env = ty::ParamEnv::empty();
137 let mut fulfill_cx = TraitEngine::new(infcx.tcx);
138 match infcx.at(&cause, param_env).eq(expected, actual) {
139 Ok(InferOk { obligations, .. }) => {
140 fulfill_cx.register_predicate_obligations(infcx, obligations);
143 infcx.report_mismatched_types(cause, expected, actual, err).emit();
148 match fulfill_cx.select_all_or_error(infcx) {
151 infcx.report_fulfillment_errors(&errors, None, false);
158 fn check_main_fn_ty(tcx: TyCtxt<'_>, main_def_id: DefId) {
159 let main_id = tcx.hir().as_local_hir_id(main_def_id).unwrap();
160 let main_span = tcx.def_span(main_def_id);
161 let main_t = tcx.type_of(main_def_id);
164 if let Some(Node::Item(it)) = tcx.hir().find(main_id) {
165 if let hir::ItemKind::Fn(.., ref generics, _) = it.kind {
166 let mut error = false;
167 if !generics.params.is_empty() {
168 let msg = "`main` function is not allowed to have generic \
171 let label = "`main` cannot have generic parameters".to_string();
172 struct_span_err!(tcx.sess, generics.span, E0131, "{}", msg)
173 .span_label(generics.span, label)
177 if let Some(sp) = generics.where_clause.span() {
182 "`main` function is not allowed to have a `where` clause"
184 .span_label(sp, "`main` cannot have a `where` clause")
194 let actual = tcx.fn_sig(main_def_id);
195 let expected_return_type = if tcx.lang_items().termination().is_some() {
196 // we take the return type of the given main function, the real check is done
198 actual.output().skip_binder()
200 // standard () main return type
204 let se_ty = tcx.mk_fn_ptr(ty::Binder::bind(tcx.mk_fn_sig(
206 expected_return_type,
208 hir::Unsafety::Normal,
214 &ObligationCause::new(main_span, main_id, ObligationCauseCode::MainFunctionType),
216 tcx.mk_fn_ptr(actual),
220 span_bug!(main_span, "main has a non-function type: found `{}`", main_t);
225 fn check_start_fn_ty(tcx: TyCtxt<'_>, start_def_id: DefId) {
226 let start_id = tcx.hir().as_local_hir_id(start_def_id).unwrap();
227 let start_span = tcx.def_span(start_def_id);
228 let start_t = tcx.type_of(start_def_id);
231 if let Some(Node::Item(it)) = tcx.hir().find(start_id) {
232 if let hir::ItemKind::Fn(.., ref generics, _) = it.kind {
233 let mut error = false;
234 if !generics.params.is_empty() {
239 "start function is not allowed to have type parameters"
241 .span_label(generics.span, "start function cannot have type parameters")
245 if let Some(sp) = generics.where_clause.span() {
250 "start function is not allowed to have a `where` clause"
252 .span_label(sp, "start function cannot have a `where` clause")
262 let se_ty = tcx.mk_fn_ptr(ty::Binder::bind(tcx.mk_fn_sig(
263 [tcx.types.isize, tcx.mk_imm_ptr(tcx.mk_imm_ptr(tcx.types.u8))].iter().cloned(),
266 hir::Unsafety::Normal,
272 &ObligationCause::new(start_span, start_id, ObligationCauseCode::StartFunctionType),
274 tcx.mk_fn_ptr(tcx.fn_sig(start_def_id)),
278 span_bug!(start_span, "start has a non-function type: found `{}`", start_t);
283 fn check_for_entry_fn(tcx: TyCtxt<'_>) {
284 match tcx.entry_fn(LOCAL_CRATE) {
285 Some((def_id, EntryFnType::Main)) => check_main_fn_ty(tcx, def_id),
286 Some((def_id, EntryFnType::Start)) => check_start_fn_ty(tcx, def_id),
291 pub fn provide(providers: &mut Providers<'_>) {
292 collect::provide(providers);
293 coherence::provide(providers);
294 check::provide(providers);
295 variance::provide(providers);
296 outlives::provide(providers);
297 impl_wf_check::provide(providers);
300 pub fn check_crate(tcx: TyCtxt<'_>) -> Result<(), ErrorReported> {
301 let _prof_timer = tcx.sess.timer("type_check_crate");
303 // this ensures that later parts of type checking can assume that items
304 // have valid types and not error
305 // FIXME(matthewjasper) We shouldn't need to do this.
306 tcx.sess.track_errors(|| {
307 tcx.sess.time("type_collecting", || {
308 for &module in tcx.hir().krate().modules.keys() {
309 tcx.ensure().collect_mod_item_types(tcx.hir().local_def_id(module));
314 if tcx.features().rustc_attrs {
315 tcx.sess.track_errors(|| {
316 tcx.sess.time("outlives_testing", || outlives::test::test_inferred_outlives(tcx));
320 tcx.sess.track_errors(|| {
321 tcx.sess.time("impl_wf_inference", || impl_wf_check::impl_wf_check(tcx));
324 tcx.sess.track_errors(|| {
325 tcx.sess.time("coherence_checking", || coherence::check_coherence(tcx));
328 if tcx.features().rustc_attrs {
329 tcx.sess.track_errors(|| {
330 tcx.sess.time("variance_testing", || variance::test::test_variance(tcx));
334 tcx.sess.track_errors(|| {
335 tcx.sess.time("wf_checking", || check::check_wf_new(tcx));
338 tcx.sess.time("item_types_checking", || {
339 for &module in tcx.hir().krate().modules.keys() {
340 tcx.ensure().check_mod_item_types(tcx.hir().local_def_id(module));
344 tcx.sess.time("item_bodies_checking", || tcx.typeck_item_bodies(LOCAL_CRATE));
346 check_unused::check_crate(tcx);
347 check_for_entry_fn(tcx);
349 if tcx.sess.err_count() == 0 { Ok(()) } else { Err(ErrorReported) }
352 /// A quasi-deprecated helper used in rustdoc and clippy to get
353 /// the type from a HIR node.
354 pub fn hir_ty_to_ty<'tcx>(tcx: TyCtxt<'tcx>, hir_ty: &hir::Ty<'_>) -> Ty<'tcx> {
355 // In case there are any projections, etc., find the "environment"
356 // def-ID that will be used to determine the traits/predicates in
357 // scope. This is derived from the enclosing item-like thing.
358 let env_node_id = tcx.hir().get_parent_item(hir_ty.hir_id);
359 let env_def_id = tcx.hir().local_def_id(env_node_id);
360 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id);
362 astconv::AstConv::ast_ty_to_ty(&item_cx, hir_ty)
365 pub fn hir_trait_to_predicates<'tcx>(
367 hir_trait: &hir::TraitRef<'_>,
369 // In case there are any projections, etc., find the "environment"
370 // def-ID that will be used to determine the traits/predicates in
371 // scope. This is derived from the enclosing item-like thing.
372 let env_hir_id = tcx.hir().get_parent_item(hir_trait.hir_ref_id);
373 let env_def_id = tcx.hir().local_def_id(env_hir_id);
374 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id);
375 let mut bounds = Bounds::default();
376 let _ = AstConv::instantiate_poly_trait_ref_inner(
380 hir::Constness::NotConst,