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;
87 mod structured_errors;
93 use rustc::session::config::EntryFnType;
94 use rustc::ty::query::Providers;
95 use rustc::ty::subst::SubstsRef;
96 use rustc::ty::{self, Ty, TyCtxt};
98 use rustc::util::common::ErrorReported;
99 use rustc_errors::struct_span_err;
100 use rustc_hir as hir;
101 use rustc_hir::def_id::{DefId, LOCAL_CRATE};
103 use rustc_infer::infer::{InferOk, TyCtxtInferExt};
104 use rustc_infer::traits::{ObligationCause, ObligationCauseCode, TraitEngine, TraitEngineExt};
105 use rustc_span::{Span, DUMMY_SP};
106 use rustc_target::spec::abi::Abi;
110 use astconv::{AstConv, Bounds};
111 pub struct TypeAndSubsts<'tcx> {
112 substs: SubstsRef<'tcx>,
116 fn require_c_abi_if_c_variadic(tcx: TyCtxt<'_>, decl: &hir::FnDecl<'_>, abi: Abi, span: Span) {
117 if decl.c_variadic && !(abi == Abi::C || abi == Abi::Cdecl) {
118 let mut err = struct_span_err!(
122 "C-variadic function must have C or cdecl calling convention"
124 err.span_label(span, "C-variadics require C or cdecl calling convention").emit();
128 fn require_same_types<'tcx>(
130 cause: &ObligationCause<'tcx>,
134 tcx.infer_ctxt().enter(|ref infcx| {
135 let param_env = ty::ParamEnv::empty();
136 let mut fulfill_cx = TraitEngine::new(infcx.tcx);
137 match infcx.at(&cause, param_env).eq(expected, actual) {
138 Ok(InferOk { obligations, .. }) => {
139 fulfill_cx.register_predicate_obligations(infcx, obligations);
142 infcx.report_mismatched_types(cause, expected, actual, err).emit();
147 match fulfill_cx.select_all_or_error(infcx) {
150 infcx.report_fulfillment_errors(&errors, None, false);
157 fn check_main_fn_ty(tcx: TyCtxt<'_>, main_def_id: DefId) {
158 let main_id = tcx.hir().as_local_hir_id(main_def_id).unwrap();
159 let main_span = tcx.def_span(main_def_id);
160 let main_t = tcx.type_of(main_def_id);
163 if let Some(Node::Item(it)) = tcx.hir().find(main_id) {
164 if let hir::ItemKind::Fn(.., ref generics, _) = it.kind {
165 let mut error = false;
166 if !generics.params.is_empty() {
167 let msg = "`main` function is not allowed to have generic \
170 let label = "`main` cannot have generic parameters".to_string();
171 struct_span_err!(tcx.sess, generics.span, E0131, "{}", msg)
172 .span_label(generics.span, label)
176 if let Some(sp) = generics.where_clause.span() {
181 "`main` function is not allowed to have a `where` clause"
183 .span_label(sp, "`main` cannot have a `where` clause")
193 let actual = tcx.fn_sig(main_def_id);
194 let expected_return_type = if tcx.lang_items().termination().is_some() {
195 // we take the return type of the given main function, the real check is done
197 actual.output().skip_binder()
199 // standard () main return type
203 let se_ty = tcx.mk_fn_ptr(ty::Binder::bind(tcx.mk_fn_sig(
205 expected_return_type,
207 hir::Unsafety::Normal,
213 &ObligationCause::new(main_span, main_id, ObligationCauseCode::MainFunctionType),
215 tcx.mk_fn_ptr(actual),
219 span_bug!(main_span, "main has a non-function type: found `{}`", main_t);
224 fn check_start_fn_ty(tcx: TyCtxt<'_>, start_def_id: DefId) {
225 let start_id = tcx.hir().as_local_hir_id(start_def_id).unwrap();
226 let start_span = tcx.def_span(start_def_id);
227 let start_t = tcx.type_of(start_def_id);
230 if let Some(Node::Item(it)) = tcx.hir().find(start_id) {
231 if let hir::ItemKind::Fn(.., ref generics, _) = it.kind {
232 let mut error = false;
233 if !generics.params.is_empty() {
238 "start function is not allowed to have type parameters"
240 .span_label(generics.span, "start function cannot have type parameters")
244 if let Some(sp) = generics.where_clause.span() {
249 "start function is not allowed to have a `where` clause"
251 .span_label(sp, "start function cannot have a `where` clause")
261 let se_ty = tcx.mk_fn_ptr(ty::Binder::bind(tcx.mk_fn_sig(
262 [tcx.types.isize, tcx.mk_imm_ptr(tcx.mk_imm_ptr(tcx.types.u8))].iter().cloned(),
265 hir::Unsafety::Normal,
271 &ObligationCause::new(start_span, start_id, ObligationCauseCode::StartFunctionType),
273 tcx.mk_fn_ptr(tcx.fn_sig(start_def_id)),
277 span_bug!(start_span, "start has a non-function type: found `{}`", start_t);
282 fn check_for_entry_fn(tcx: TyCtxt<'_>) {
283 match tcx.entry_fn(LOCAL_CRATE) {
284 Some((def_id, EntryFnType::Main)) => check_main_fn_ty(tcx, def_id),
285 Some((def_id, EntryFnType::Start)) => check_start_fn_ty(tcx, def_id),
290 pub fn provide(providers: &mut Providers<'_>) {
291 collect::provide(providers);
292 coherence::provide(providers);
293 check::provide(providers);
294 variance::provide(providers);
295 outlives::provide(providers);
296 impl_wf_check::provide(providers);
299 pub fn check_crate(tcx: TyCtxt<'_>) -> Result<(), ErrorReported> {
300 let _prof_timer = tcx.sess.timer("type_check_crate");
302 // this ensures that later parts of type checking can assume that items
303 // have valid types and not error
304 // FIXME(matthewjasper) We shouldn't need to do this.
305 tcx.sess.track_errors(|| {
306 tcx.sess.time("type_collecting", || {
307 for &module in tcx.hir().krate().modules.keys() {
308 tcx.ensure().collect_mod_item_types(tcx.hir().local_def_id(module));
313 if tcx.features().rustc_attrs {
314 tcx.sess.track_errors(|| {
315 tcx.sess.time("outlives_testing", || outlives::test::test_inferred_outlives(tcx));
319 tcx.sess.track_errors(|| {
320 tcx.sess.time("impl_wf_inference", || impl_wf_check::impl_wf_check(tcx));
323 tcx.sess.track_errors(|| {
324 tcx.sess.time("coherence_checking", || coherence::check_coherence(tcx));
327 if tcx.features().rustc_attrs {
328 tcx.sess.track_errors(|| {
329 tcx.sess.time("variance_testing", || variance::test::test_variance(tcx));
333 tcx.sess.track_errors(|| {
334 tcx.sess.time("wf_checking", || check::check_wf_new(tcx));
337 tcx.sess.time("item_types_checking", || {
338 for &module in tcx.hir().krate().modules.keys() {
339 tcx.ensure().check_mod_item_types(tcx.hir().local_def_id(module));
343 tcx.sess.time("item_bodies_checking", || tcx.typeck_item_bodies(LOCAL_CRATE));
345 check_unused::check_crate(tcx);
346 check_for_entry_fn(tcx);
348 if tcx.sess.err_count() == 0 { Ok(()) } else { Err(ErrorReported) }
351 /// A quasi-deprecated helper used in rustdoc and clippy to get
352 /// the type from a HIR node.
353 pub fn hir_ty_to_ty<'tcx>(tcx: TyCtxt<'tcx>, hir_ty: &hir::Ty<'_>) -> Ty<'tcx> {
354 // In case there are any projections, etc., find the "environment"
355 // def-ID that will be used to determine the traits/predicates in
356 // scope. This is derived from the enclosing item-like thing.
357 let env_node_id = tcx.hir().get_parent_item(hir_ty.hir_id);
358 let env_def_id = tcx.hir().local_def_id(env_node_id);
359 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id);
361 astconv::AstConv::ast_ty_to_ty(&item_cx, hir_ty)
364 pub fn hir_trait_to_predicates<'tcx>(
366 hir_trait: &hir::TraitRef<'_>,
368 // In case there are any projections, etc., find the "environment"
369 // def-ID that will be used to determine the traits/predicates in
370 // scope. This is derived from the enclosing item-like thing.
371 let env_hir_id = tcx.hir().get_parent_item(hir_trait.hir_ref_id);
372 let env_def_id = tcx.hir().local_def_id(env_hir_id);
373 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id);
374 let mut bounds = Bounds::default();
375 let _ = AstConv::instantiate_poly_trait_ref_inner(
379 hir::Constness::NotConst,