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(rustc_diagnostic_macros)]
68 #![feature(slice_patterns)]
69 #![feature(never_type)]
71 #![recursion_limit="256"]
73 #![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_generic_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::util::common::ErrorReported;
106 use rustc::session::config::{EntryFnType, nightly_options};
107 use rustc::traits::{ObligationCause, ObligationCauseCode, TraitEngine, TraitEngineExt};
108 use rustc::ty::subst::SubstsRef;
109 use rustc::ty::{self, Ty, TyCtxt};
110 use rustc::ty::query::Providers;
112 use syntax_pos::Span;
113 use util::common::time;
117 use astconv::{AstConv, Bounds};
118 pub use collect::checked_type_of;
120 pub struct TypeAndSubsts<'tcx> {
121 substs: SubstsRef<'tcx>,
125 fn check_type_alias_enum_variants_enabled<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
127 if !tcx.features().type_alias_enum_variants {
128 let mut err = tcx.sess.struct_span_err(
130 "enum variants on type aliases are experimental"
132 if nightly_options::is_nightly_build() {
134 "add `#![feature(type_alias_enum_variants)]` to the \
135 crate attributes to enable");
141 fn require_c_abi_if_c_variadic(tcx: TyCtxt<'_, '_, '_>,
145 if decl.c_variadic && !(abi == Abi::C || abi == Abi::Cdecl) {
146 let mut err = struct_span_err!(tcx.sess, span, E0045,
147 "C-variadic function must have C or cdecl calling convention");
148 err.span_label(span, "C-variadics require C or cdecl calling convention").emit();
152 fn require_same_types<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
153 cause: &ObligationCause<'tcx>,
157 tcx.infer_ctxt().enter(|ref infcx| {
158 let param_env = ty::ParamEnv::empty();
159 let mut fulfill_cx = TraitEngine::new(infcx.tcx);
160 match infcx.at(&cause, param_env).eq(expected, actual) {
161 Ok(InferOk { obligations, .. }) => {
162 fulfill_cx.register_predicate_obligations(infcx, obligations);
165 infcx.report_mismatched_types(cause, expected, actual, err).emit();
170 match fulfill_cx.select_all_or_error(infcx) {
173 infcx.report_fulfillment_errors(&errors, None, false);
180 fn check_main_fn_ty<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, main_def_id: DefId) {
181 let main_id = tcx.hir().as_local_hir_id(main_def_id).unwrap();
182 let main_span = tcx.def_span(main_def_id);
183 let main_t = tcx.type_of(main_def_id);
186 if let Some(Node::Item(it)) = tcx.hir().find_by_hir_id(main_id) {
187 if let hir::ItemKind::Fn(.., ref generics, _) = it.node {
188 let mut error = false;
189 if !generics.params.is_empty() {
190 let msg = "`main` function is not allowed to have generic \
191 parameters".to_owned();
192 let label = "`main` cannot have generic parameters".to_string();
193 struct_span_err!(tcx.sess, generics.span, E0131, "{}", msg)
194 .span_label(generics.span, label)
198 if let Some(sp) = generics.where_clause.span() {
199 struct_span_err!(tcx.sess, sp, E0646,
200 "`main` function is not allowed to have a `where` clause")
201 .span_label(sp, "`main` cannot have a `where` clause")
211 let actual = tcx.fn_sig(main_def_id);
212 let expected_return_type = if tcx.lang_items().termination().is_some() {
213 // we take the return type of the given main function, the real check is done
215 actual.output().skip_binder()
217 // standard () main return type
221 let se_ty = tcx.mk_fn_ptr(ty::Binder::bind(
224 expected_return_type,
226 hir::Unsafety::Normal,
233 &ObligationCause::new(main_span, main_id, ObligationCauseCode::MainFunctionType),
235 tcx.mk_fn_ptr(actual));
239 "main has a non-function type: found `{}`",
245 fn check_start_fn_ty<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, start_def_id: DefId) {
246 let start_id = tcx.hir().as_local_hir_id(start_def_id).unwrap();
247 let start_span = tcx.def_span(start_def_id);
248 let start_t = tcx.type_of(start_def_id);
251 if let Some(Node::Item(it)) = tcx.hir().find_by_hir_id(start_id) {
252 if let hir::ItemKind::Fn(.., ref generics, _) = it.node {
253 let mut error = false;
254 if !generics.params.is_empty() {
255 struct_span_err!(tcx.sess, generics.span, E0132,
256 "start function is not allowed to have type parameters")
257 .span_label(generics.span,
258 "start function cannot have type parameters")
262 if let Some(sp) = generics.where_clause.span() {
263 struct_span_err!(tcx.sess, sp, E0647,
264 "start function is not allowed to have a `where` clause")
265 .span_label(sp, "start function cannot have a `where` clause")
275 let se_ty = tcx.mk_fn_ptr(ty::Binder::bind(
279 tcx.mk_imm_ptr(tcx.mk_imm_ptr(tcx.types.u8))
283 hir::Unsafety::Normal,
290 &ObligationCause::new(start_span, start_id, ObligationCauseCode::StartFunctionType),
292 tcx.mk_fn_ptr(tcx.fn_sig(start_def_id)));
295 span_bug!(start_span,
296 "start has a non-function type: found `{}`",
302 fn check_for_entry_fn<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
303 match tcx.entry_fn(LOCAL_CRATE) {
304 Some((def_id, EntryFnType::Main)) => check_main_fn_ty(tcx, def_id),
305 Some((def_id, EntryFnType::Start)) => check_start_fn_ty(tcx, def_id),
310 pub fn provide(providers: &mut Providers<'_>) {
311 collect::provide(providers);
312 coherence::provide(providers);
313 check::provide(providers);
314 variance::provide(providers);
315 outlives::provide(providers);
316 impl_wf_check::provide(providers);
319 pub fn check_crate<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>)
320 -> Result<(), ErrorReported>
322 tcx.sess.profiler(|p| p.start_activity("type-check crate"));
324 // this ensures that later parts of type checking can assume that items
325 // have valid types and not error
326 tcx.sess.track_errors(|| {
327 time(tcx.sess, "type collecting", || {
328 for &module in tcx.hir().krate().modules.keys() {
329 tcx.ensure().collect_mod_item_types(tcx.hir().local_def_id(module));
334 if tcx.features().rustc_attrs {
335 tcx.sess.track_errors(|| {
336 time(tcx.sess, "outlives testing", ||
337 outlives::test::test_inferred_outlives(tcx));
341 tcx.sess.track_errors(|| {
342 time(tcx.sess, "impl wf inference", ||
343 impl_wf_check::impl_wf_check(tcx));
346 tcx.sess.track_errors(|| {
347 time(tcx.sess, "coherence checking", ||
348 coherence::check_coherence(tcx));
351 if tcx.features().rustc_attrs {
352 tcx.sess.track_errors(|| {
353 time(tcx.sess, "variance testing", ||
354 variance::test::test_variance(tcx));
358 time(tcx.sess, "wf checking", || check::check_wf_new(tcx))?;
360 time(tcx.sess, "item-types checking", || {
361 for &module in tcx.hir().krate().modules.keys() {
362 tcx.ensure().check_mod_item_types(tcx.hir().local_def_id(module));
366 time(tcx.sess, "item-bodies checking", || tcx.typeck_item_bodies(LOCAL_CRATE));
368 check_unused::check_crate(tcx);
369 check_for_entry_fn(tcx);
371 tcx.sess.profiler(|p| p.end_activity("type-check crate"));
373 if tcx.sess.err_count() == 0 {
380 /// A quasi-deprecated helper used in rustdoc and clippy to get
381 /// the type from a HIR node.
382 pub fn hir_ty_to_ty<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, hir_ty: &hir::Ty) -> Ty<'tcx> {
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_item(hir_ty.hir_id);
387 let env_def_id = tcx.hir().local_def_id_from_hir_id(env_node_id);
388 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id);
390 astconv::AstConv::ast_ty_to_ty(&item_cx, hir_ty)
393 pub fn hir_trait_to_predicates<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, hir_trait: &hir::TraitRef)
394 -> (ty::PolyTraitRef<'tcx>, Bounds<'tcx>) {
395 // In case there are any projections, etc., find the "environment"
396 // def-ID that will be used to determine the traits/predicates in
397 // scope. This is derived from the enclosing item-like thing.
398 let env_hir_id = tcx.hir().get_parent_item(hir_trait.hir_ref_id);
399 let env_def_id = tcx.hir().local_def_id_from_hir_id(env_hir_id);
400 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id);
401 let mut bounds = Bounds::default();
402 let (principal, _) = AstConv::instantiate_poly_trait_ref_inner(
403 &item_cx, hir_trait, tcx.types.err, &mut bounds, true
409 __build_diagnostic_array! { librustc_typeck, DIAGNOSTICS }