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/")]
60 #![allow(non_camel_case_types)]
62 #![feature(box_patterns)]
63 #![feature(box_syntax)]
64 #![feature(crate_visibility_modifier)]
65 #![feature(exhaustive_patterns)]
67 #![feature(refcell_replace_swap)]
68 #![feature(rustc_diagnostic_macros)]
69 #![feature(slice_patterns)]
70 #![feature(never_type)]
72 #![recursion_limit="256"]
74 #![deny(rust_2018_idioms)]
75 #![allow(explicit_outlives_requirements)]
77 #[macro_use] extern crate log;
78 #[macro_use] extern crate syntax;
80 #[macro_use] extern crate rustc;
82 // N.B., this module needs to be declared first so diagnostics are
83 // registered before they are used.
91 mod constrained_type_params;
92 mod structured_errors;
98 use rustc_target::spec::abi::Abi;
99 use rustc::hir::{self, Node};
100 use rustc::hir::def_id::{DefId, LOCAL_CRATE};
101 use rustc::infer::InferOk;
105 use rustc::session::CompileIncomplete;
106 use rustc::session::config::{EntryFnType, nightly_options};
107 use rustc::traits::{ObligationCause, ObligationCauseCode, TraitEngine, TraitEngineExt};
108 use rustc::ty::subst::Substs;
109 use rustc::ty::{self, Ty, TyCtxt};
110 use rustc::ty::query::Providers;
112 use rustc::util::profiling::ProfileCategory;
113 use syntax_pos::Span;
114 use util::common::time;
118 pub struct TypeAndSubsts<'tcx> {
119 substs: &'tcx Substs<'tcx>,
123 fn check_type_alias_enum_variants_enabled<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
125 if !tcx.features().type_alias_enum_variants {
126 let mut err = tcx.sess.struct_span_err(
128 "enum variants on type aliases are experimental"
130 if nightly_options::is_nightly_build() {
132 "add `#![feature(type_alias_enum_variants)]` to the \
133 crate attributes to enable");
139 fn require_c_abi_if_variadic(tcx: TyCtxt<'_, '_, '_>,
143 if decl.variadic && !(abi == Abi::C || abi == Abi::Cdecl) {
144 let mut err = struct_span_err!(tcx.sess, span, E0045,
145 "variadic function must have C or cdecl calling convention");
146 err.span_label(span, "variadics require C or cdecl calling convention").emit();
150 fn require_same_types<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
151 cause: &ObligationCause<'tcx>,
155 tcx.infer_ctxt().enter(|ref infcx| {
156 let param_env = ty::ParamEnv::empty();
157 let mut fulfill_cx = TraitEngine::new(infcx.tcx);
158 match infcx.at(&cause, param_env).eq(expected, actual) {
159 Ok(InferOk { obligations, .. }) => {
160 fulfill_cx.register_predicate_obligations(infcx, obligations);
163 infcx.report_mismatched_types(cause, expected, actual, err).emit();
168 match fulfill_cx.select_all_or_error(infcx) {
171 infcx.report_fulfillment_errors(&errors, None, false);
178 fn check_main_fn_ty<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, main_def_id: DefId) {
179 let main_id = tcx.hir().as_local_hir_id(main_def_id).unwrap();
180 let main_span = tcx.def_span(main_def_id);
181 let main_t = tcx.type_of(main_def_id);
184 if let Some(Node::Item(it)) = tcx.hir().find_by_hir_id(main_id) {
185 if let hir::ItemKind::Fn(.., ref generics, _) = it.node {
186 let mut error = false;
187 if !generics.params.is_empty() {
188 let msg = "`main` function is not allowed to have generic \
189 parameters".to_owned();
190 let label = "`main` cannot have generic parameters".to_string();
191 struct_span_err!(tcx.sess, generics.span, E0131, "{}", msg)
192 .span_label(generics.span, label)
196 if let Some(sp) = generics.where_clause.span() {
197 struct_span_err!(tcx.sess, sp, E0646,
198 "`main` function is not allowed to have a `where` clause")
199 .span_label(sp, "`main` cannot have a `where` clause")
209 let actual = tcx.fn_sig(main_def_id);
210 let expected_return_type = if tcx.lang_items().termination().is_some() {
211 // we take the return type of the given main function, the real check is done
213 actual.output().skip_binder()
215 // standard () main return type
219 let se_ty = tcx.mk_fn_ptr(ty::Binder::bind(
222 expected_return_type,
224 hir::Unsafety::Normal,
231 &ObligationCause::new(main_span, main_id, ObligationCauseCode::MainFunctionType),
233 tcx.mk_fn_ptr(actual));
237 "main has a non-function type: found `{}`",
243 fn check_start_fn_ty<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, start_def_id: DefId) {
244 let start_id = tcx.hir().as_local_hir_id(start_def_id).unwrap();
245 let start_span = tcx.def_span(start_def_id);
246 let start_t = tcx.type_of(start_def_id);
249 if let Some(Node::Item(it)) = tcx.hir().find_by_hir_id(start_id) {
250 if let hir::ItemKind::Fn(.., ref generics, _) = it.node {
251 let mut error = false;
252 if !generics.params.is_empty() {
253 struct_span_err!(tcx.sess, generics.span, E0132,
254 "start function is not allowed to have type parameters")
255 .span_label(generics.span,
256 "start function cannot have type parameters")
260 if let Some(sp) = generics.where_clause.span() {
261 struct_span_err!(tcx.sess, sp, E0647,
262 "start function is not allowed to have a `where` clause")
263 .span_label(sp, "start function cannot have a `where` clause")
273 let se_ty = tcx.mk_fn_ptr(ty::Binder::bind(
277 tcx.mk_imm_ptr(tcx.mk_imm_ptr(tcx.types.u8))
281 hir::Unsafety::Normal,
288 &ObligationCause::new(start_span, start_id, ObligationCauseCode::StartFunctionType),
290 tcx.mk_fn_ptr(tcx.fn_sig(start_def_id)));
293 span_bug!(start_span,
294 "start has a non-function type: found `{}`",
300 fn check_for_entry_fn<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
301 match tcx.entry_fn(LOCAL_CRATE) {
302 Some((def_id, EntryFnType::Main)) => check_main_fn_ty(tcx, def_id),
303 Some((def_id, EntryFnType::Start)) => check_start_fn_ty(tcx, def_id),
308 pub fn provide(providers: &mut Providers<'_>) {
309 collect::provide(providers);
310 coherence::provide(providers);
311 check::provide(providers);
312 variance::provide(providers);
313 outlives::provide(providers);
314 impl_wf_check::provide(providers);
317 pub fn check_crate<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>)
318 -> Result<(), CompileIncomplete>
320 tcx.sess.profiler(|p| p.start_activity(ProfileCategory::TypeChecking));
322 // this ensures that later parts of type checking can assume that items
323 // have valid types and not error
324 tcx.sess.track_errors(|| {
325 time(tcx.sess, "type collecting", ||
326 collect::collect_item_types(tcx));
330 if tcx.features().rustc_attrs {
331 tcx.sess.track_errors(|| {
332 time(tcx.sess, "outlives testing", ||
333 outlives::test::test_inferred_outlives(tcx));
337 tcx.sess.track_errors(|| {
338 time(tcx.sess, "impl wf inference", ||
339 impl_wf_check::impl_wf_check(tcx));
342 tcx.sess.track_errors(|| {
343 time(tcx.sess, "coherence checking", ||
344 coherence::check_coherence(tcx));
347 if tcx.features().rustc_attrs {
348 tcx.sess.track_errors(|| {
349 time(tcx.sess, "variance testing", ||
350 variance::test::test_variance(tcx));
354 time(tcx.sess, "wf checking", || check::check_wf_new(tcx))?;
356 time(tcx.sess, "item-types checking", || check::check_item_types(tcx))?;
358 time(tcx.sess, "item-bodies checking", || check::check_item_bodies(tcx))?;
360 check_unused::check_crate(tcx);
361 check_for_entry_fn(tcx);
363 tcx.sess.profiler(|p| p.end_activity(ProfileCategory::TypeChecking));
365 tcx.sess.compile_status()
368 /// A quasi-deprecated helper used in rustdoc and save-analysis to get
369 /// the type from a HIR node.
370 pub fn hir_ty_to_ty<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, hir_ty: &hir::Ty) -> Ty<'tcx> {
371 // In case there are any projections etc, find the "environment"
372 // def-id that will be used to determine the traits/predicates in
373 // scope. This is derived from the enclosing item-like thing.
374 let env_node_id = tcx.hir().get_parent_item(hir_ty.hir_id);
375 let env_def_id = tcx.hir().local_def_id_from_hir_id(env_node_id);
376 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id);
378 astconv::AstConv::ast_ty_to_ty(&item_cx, hir_ty)
381 pub fn hir_trait_to_predicates<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, hir_trait: &hir::TraitRef)
382 -> (ty::PolyTraitRef<'tcx>, Vec<(ty::PolyProjectionPredicate<'tcx>, Span)>) {
383 // In case there are any projections etc, find the "environment"
384 // def-id that will be used to determine the traits/predicates in
385 // scope. This is derived from the enclosing item-like thing.
386 let env_node_id = tcx.hir().get_parent(hir_trait.ref_id);
387 let env_def_id = tcx.hir().local_def_id(env_node_id);
388 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id);
389 let mut projections = Vec::new();
390 let (principal, _) = astconv::AstConv::instantiate_poly_trait_ref_inner(
391 &item_cx, hir_trait, tcx.types.err, &mut projections, true
394 (principal, projections)
397 __build_diagnostic_array! { librustc_typeck, DIAGNOSTICS }