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 #![deny(unused_lifetimes)]
76 #![allow(explicit_outlives_requirements)]
78 #[macro_use] extern crate log;
79 #[macro_use] extern crate syntax;
81 #[macro_use] extern crate rustc;
83 // N.B., this module needs to be declared first so diagnostics are
84 // registered before they are used.
92 mod constrained_generic_params;
93 mod structured_errors;
99 use rustc_target::spec::abi::Abi;
100 use rustc::hir::{self, Node};
101 use rustc::hir::def_id::{DefId, LOCAL_CRATE};
102 use rustc::infer::InferOk;
106 use rustc::util::common::ErrorReported;
107 use rustc::session::config::{EntryFnType, nightly_options};
108 use rustc::traits::{ObligationCause, ObligationCauseCode, TraitEngine, TraitEngineExt};
109 use rustc::ty::subst::SubstsRef;
110 use rustc::ty::{self, Ty, TyCtxt};
111 use rustc::ty::query::Providers;
113 use syntax_pos::Span;
114 use util::common::time;
118 use astconv::{AstConv, Bounds};
119 pub use collect::checked_type_of;
121 pub struct TypeAndSubsts<'tcx> {
122 substs: SubstsRef<'tcx>,
126 fn check_type_alias_enum_variants_enabled<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
128 if !tcx.features().type_alias_enum_variants {
129 let mut err = tcx.sess.struct_span_err(
131 "enum variants on type aliases are experimental"
133 if nightly_options::is_nightly_build() {
135 "add `#![feature(type_alias_enum_variants)]` to the \
136 crate attributes to enable");
142 fn require_c_abi_if_c_variadic(tcx: TyCtxt<'_, '_, '_>,
146 if decl.c_variadic && !(abi == Abi::C || abi == Abi::Cdecl) {
147 let mut err = struct_span_err!(tcx.sess, span, E0045,
148 "C-variadic function must have C or cdecl calling convention");
149 err.span_label(span, "C-variadics require C or cdecl calling convention").emit();
153 fn require_same_types<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
154 cause: &ObligationCause<'tcx>,
158 tcx.infer_ctxt().enter(|ref infcx| {
159 let param_env = ty::ParamEnv::empty();
160 let mut fulfill_cx = TraitEngine::new(infcx.tcx);
161 match infcx.at(&cause, param_env).eq(expected, actual) {
162 Ok(InferOk { obligations, .. }) => {
163 fulfill_cx.register_predicate_obligations(infcx, obligations);
166 infcx.report_mismatched_types(cause, expected, actual, err).emit();
171 match fulfill_cx.select_all_or_error(infcx) {
174 infcx.report_fulfillment_errors(&errors, None, false);
181 fn check_main_fn_ty<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, main_def_id: DefId) {
182 let main_id = tcx.hir().as_local_hir_id(main_def_id).unwrap();
183 let main_span = tcx.def_span(main_def_id);
184 let main_t = tcx.type_of(main_def_id);
187 if let Some(Node::Item(it)) = tcx.hir().find_by_hir_id(main_id) {
188 if let hir::ItemKind::Fn(.., ref generics, _) = it.node {
189 let mut error = false;
190 if !generics.params.is_empty() {
191 let msg = "`main` function is not allowed to have generic \
192 parameters".to_owned();
193 let label = "`main` cannot have generic parameters".to_string();
194 struct_span_err!(tcx.sess, generics.span, E0131, "{}", msg)
195 .span_label(generics.span, label)
199 if let Some(sp) = generics.where_clause.span() {
200 struct_span_err!(tcx.sess, sp, E0646,
201 "`main` function is not allowed to have a `where` clause")
202 .span_label(sp, "`main` cannot have a `where` clause")
212 let actual = tcx.fn_sig(main_def_id);
213 let expected_return_type = if tcx.lang_items().termination().is_some() {
214 // we take the return type of the given main function, the real check is done
216 actual.output().skip_binder()
218 // standard () main return type
222 let se_ty = tcx.mk_fn_ptr(ty::Binder::bind(
225 expected_return_type,
227 hir::Unsafety::Normal,
234 &ObligationCause::new(main_span, main_id, ObligationCauseCode::MainFunctionType),
236 tcx.mk_fn_ptr(actual));
240 "main has a non-function type: found `{}`",
246 fn check_start_fn_ty<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, start_def_id: DefId) {
247 let start_id = tcx.hir().as_local_hir_id(start_def_id).unwrap();
248 let start_span = tcx.def_span(start_def_id);
249 let start_t = tcx.type_of(start_def_id);
252 if let Some(Node::Item(it)) = tcx.hir().find_by_hir_id(start_id) {
253 if let hir::ItemKind::Fn(.., ref generics, _) = it.node {
254 let mut error = false;
255 if !generics.params.is_empty() {
256 struct_span_err!(tcx.sess, generics.span, E0132,
257 "start function is not allowed to have type parameters")
258 .span_label(generics.span,
259 "start function cannot have type parameters")
263 if let Some(sp) = generics.where_clause.span() {
264 struct_span_err!(tcx.sess, sp, E0647,
265 "start function is not allowed to have a `where` clause")
266 .span_label(sp, "start function cannot have a `where` clause")
276 let se_ty = tcx.mk_fn_ptr(ty::Binder::bind(
280 tcx.mk_imm_ptr(tcx.mk_imm_ptr(tcx.types.u8))
284 hir::Unsafety::Normal,
291 &ObligationCause::new(start_span, start_id, ObligationCauseCode::StartFunctionType),
293 tcx.mk_fn_ptr(tcx.fn_sig(start_def_id)));
296 span_bug!(start_span,
297 "start has a non-function type: found `{}`",
303 fn check_for_entry_fn<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
304 match tcx.entry_fn(LOCAL_CRATE) {
305 Some((def_id, EntryFnType::Main)) => check_main_fn_ty(tcx, def_id),
306 Some((def_id, EntryFnType::Start)) => check_start_fn_ty(tcx, def_id),
311 pub fn provide(providers: &mut Providers<'_>) {
312 collect::provide(providers);
313 coherence::provide(providers);
314 check::provide(providers);
315 variance::provide(providers);
316 outlives::provide(providers);
317 impl_wf_check::provide(providers);
320 pub fn check_crate<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>)
321 -> Result<(), ErrorReported>
323 tcx.sess.profiler(|p| p.start_activity("type-check crate"));
325 // this ensures that later parts of type checking can assume that items
326 // have valid types and not error
327 tcx.sess.track_errors(|| {
328 time(tcx.sess, "type collecting", || {
329 for &module in tcx.hir().krate().modules.keys() {
330 tcx.ensure().collect_mod_item_types(tcx.hir().local_def_id(module));
335 if tcx.features().rustc_attrs {
336 tcx.sess.track_errors(|| {
337 time(tcx.sess, "outlives testing", ||
338 outlives::test::test_inferred_outlives(tcx));
342 tcx.sess.track_errors(|| {
343 time(tcx.sess, "impl wf inference", ||
344 impl_wf_check::impl_wf_check(tcx));
347 tcx.sess.track_errors(|| {
348 time(tcx.sess, "coherence checking", ||
349 coherence::check_coherence(tcx));
352 if tcx.features().rustc_attrs {
353 tcx.sess.track_errors(|| {
354 time(tcx.sess, "variance testing", ||
355 variance::test::test_variance(tcx));
359 time(tcx.sess, "wf checking", || check::check_wf_new(tcx))?;
361 time(tcx.sess, "item-types checking", || {
362 for &module in tcx.hir().krate().modules.keys() {
363 tcx.ensure().check_mod_item_types(tcx.hir().local_def_id(module));
367 time(tcx.sess, "item-bodies checking", || tcx.typeck_item_bodies(LOCAL_CRATE));
369 check_unused::check_crate(tcx);
370 check_for_entry_fn(tcx);
372 tcx.sess.profiler(|p| p.end_activity("type-check crate"));
374 if tcx.sess.err_count() == 0 {
381 /// A quasi-deprecated helper used in rustdoc and clippy to get
382 /// the type from a HIR node.
383 pub fn hir_ty_to_ty<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, hir_ty: &hir::Ty) -> Ty<'tcx> {
384 // In case there are any projections, etc., find the "environment"
385 // def-ID that will be used to determine the traits/predicates in
386 // scope. This is derived from the enclosing item-like thing.
387 let env_node_id = tcx.hir().get_parent_item(hir_ty.hir_id);
388 let env_def_id = tcx.hir().local_def_id_from_hir_id(env_node_id);
389 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id);
391 astconv::AstConv::ast_ty_to_ty(&item_cx, hir_ty)
394 pub fn hir_trait_to_predicates<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, hir_trait: &hir::TraitRef)
395 -> (ty::PolyTraitRef<'tcx>, Bounds<'tcx>) {
396 // In case there are any projections, etc., find the "environment"
397 // def-ID that will be used to determine the traits/predicates in
398 // scope. This is derived from the enclosing item-like thing.
399 let env_hir_id = tcx.hir().get_parent_item(hir_trait.hir_ref_id);
400 let env_def_id = tcx.hir().local_def_id_from_hir_id(env_hir_id);
401 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id);
402 let mut bounds = Bounds::default();
403 let (principal, _) = AstConv::instantiate_poly_trait_ref_inner(
404 &item_cx, hir_trait, tcx.types.err, &mut bounds, true
410 __build_diagnostic_array! { librustc_typeck, DIAGNOSTICS }