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 pub use collect::checked_type_of;
119 pub struct TypeAndSubsts<'tcx> {
120 substs: SubstsRef<'tcx>,
124 fn check_type_alias_enum_variants_enabled<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
126 if !tcx.features().type_alias_enum_variants {
127 let mut err = tcx.sess.struct_span_err(
129 "enum variants on type aliases are experimental"
131 if nightly_options::is_nightly_build() {
133 "add `#![feature(type_alias_enum_variants)]` to the \
134 crate attributes to enable");
140 fn require_c_abi_if_c_variadic(tcx: TyCtxt<'_, '_, '_>,
144 if decl.c_variadic && !(abi == Abi::C || abi == Abi::Cdecl) {
145 let mut err = struct_span_err!(tcx.sess, span, E0045,
146 "C-variadic function must have C or cdecl calling convention");
147 err.span_label(span, "C-variadics require C or cdecl calling convention").emit();
151 fn require_same_types<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
152 cause: &ObligationCause<'tcx>,
156 tcx.infer_ctxt().enter(|ref infcx| {
157 let param_env = ty::ParamEnv::empty();
158 let mut fulfill_cx = TraitEngine::new(infcx.tcx);
159 match infcx.at(&cause, param_env).eq(expected, actual) {
160 Ok(InferOk { obligations, .. }) => {
161 fulfill_cx.register_predicate_obligations(infcx, obligations);
164 infcx.report_mismatched_types(cause, expected, actual, err).emit();
169 match fulfill_cx.select_all_or_error(infcx) {
172 infcx.report_fulfillment_errors(&errors, None, false);
179 fn check_main_fn_ty<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, main_def_id: DefId) {
180 let main_id = tcx.hir().as_local_hir_id(main_def_id).unwrap();
181 let main_span = tcx.def_span(main_def_id);
182 let main_t = tcx.type_of(main_def_id);
185 if let Some(Node::Item(it)) = tcx.hir().find_by_hir_id(main_id) {
186 if let hir::ItemKind::Fn(.., ref generics, _) = it.node {
187 let mut error = false;
188 if !generics.params.is_empty() {
189 let msg = "`main` function is not allowed to have generic \
190 parameters".to_owned();
191 let label = "`main` cannot have generic parameters".to_string();
192 struct_span_err!(tcx.sess, generics.span, E0131, "{}", msg)
193 .span_label(generics.span, label)
197 if let Some(sp) = generics.where_clause.span() {
198 struct_span_err!(tcx.sess, sp, E0646,
199 "`main` function is not allowed to have a `where` clause")
200 .span_label(sp, "`main` cannot have a `where` clause")
210 let actual = tcx.fn_sig(main_def_id);
211 let expected_return_type = if tcx.lang_items().termination().is_some() {
212 // we take the return type of the given main function, the real check is done
214 actual.output().skip_binder()
216 // standard () main return type
220 let se_ty = tcx.mk_fn_ptr(ty::Binder::bind(
223 expected_return_type,
225 hir::Unsafety::Normal,
232 &ObligationCause::new(main_span, main_id, ObligationCauseCode::MainFunctionType),
234 tcx.mk_fn_ptr(actual));
238 "main has a non-function type: found `{}`",
244 fn check_start_fn_ty<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, start_def_id: DefId) {
245 let start_id = tcx.hir().as_local_hir_id(start_def_id).unwrap();
246 let start_span = tcx.def_span(start_def_id);
247 let start_t = tcx.type_of(start_def_id);
250 if let Some(Node::Item(it)) = tcx.hir().find_by_hir_id(start_id) {
251 if let hir::ItemKind::Fn(.., ref generics, _) = it.node {
252 let mut error = false;
253 if !generics.params.is_empty() {
254 struct_span_err!(tcx.sess, generics.span, E0132,
255 "start function is not allowed to have type parameters")
256 .span_label(generics.span,
257 "start function cannot have type parameters")
261 if let Some(sp) = generics.where_clause.span() {
262 struct_span_err!(tcx.sess, sp, E0647,
263 "start function is not allowed to have a `where` clause")
264 .span_label(sp, "start function cannot have a `where` clause")
274 let se_ty = tcx.mk_fn_ptr(ty::Binder::bind(
278 tcx.mk_imm_ptr(tcx.mk_imm_ptr(tcx.types.u8))
282 hir::Unsafety::Normal,
289 &ObligationCause::new(start_span, start_id, ObligationCauseCode::StartFunctionType),
291 tcx.mk_fn_ptr(tcx.fn_sig(start_def_id)));
294 span_bug!(start_span,
295 "start has a non-function type: found `{}`",
301 fn check_for_entry_fn<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
302 match tcx.entry_fn(LOCAL_CRATE) {
303 Some((def_id, EntryFnType::Main)) => check_main_fn_ty(tcx, def_id),
304 Some((def_id, EntryFnType::Start)) => check_start_fn_ty(tcx, def_id),
309 pub fn provide(providers: &mut Providers<'_>) {
310 collect::provide(providers);
311 coherence::provide(providers);
312 check::provide(providers);
313 variance::provide(providers);
314 outlives::provide(providers);
315 impl_wf_check::provide(providers);
318 pub fn check_crate<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>)
319 -> Result<(), ErrorReported>
321 tcx.sess.profiler(|p| p.start_activity("type-check crate"));
323 // this ensures that later parts of type checking can assume that items
324 // have valid types and not error
325 tcx.sess.track_errors(|| {
326 time(tcx.sess, "type collecting", || {
327 for &module in tcx.hir().krate().modules.keys() {
328 tcx.ensure().collect_mod_item_types(tcx.hir().local_def_id(module));
333 if tcx.features().rustc_attrs {
334 tcx.sess.track_errors(|| {
335 time(tcx.sess, "outlives testing", ||
336 outlives::test::test_inferred_outlives(tcx));
340 tcx.sess.track_errors(|| {
341 time(tcx.sess, "impl wf inference", ||
342 impl_wf_check::impl_wf_check(tcx));
345 tcx.sess.track_errors(|| {
346 time(tcx.sess, "coherence checking", ||
347 coherence::check_coherence(tcx));
350 if tcx.features().rustc_attrs {
351 tcx.sess.track_errors(|| {
352 time(tcx.sess, "variance testing", ||
353 variance::test::test_variance(tcx));
357 time(tcx.sess, "wf checking", || check::check_wf_new(tcx))?;
359 time(tcx.sess, "item-types checking", || {
360 for &module in tcx.hir().krate().modules.keys() {
361 tcx.ensure().check_mod_item_types(tcx.hir().local_def_id(module));
365 time(tcx.sess, "item-bodies checking", || tcx.typeck_item_bodies(LOCAL_CRATE));
367 check_unused::check_crate(tcx);
368 check_for_entry_fn(tcx);
370 tcx.sess.profiler(|p| p.end_activity("type-check crate"));
372 if tcx.sess.err_count() == 0 {
379 /// A quasi-deprecated helper used in rustdoc and clippy to get
380 /// the type from a HIR node.
381 pub fn hir_ty_to_ty<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, hir_ty: &hir::Ty) -> Ty<'tcx> {
382 // In case there are any projections etc, find the "environment"
383 // def-id that will be used to determine the traits/predicates in
384 // scope. This is derived from the enclosing item-like thing.
385 let env_node_id = tcx.hir().get_parent_item(hir_ty.hir_id);
386 let env_def_id = tcx.hir().local_def_id_from_hir_id(env_node_id);
387 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id);
389 astconv::AstConv::ast_ty_to_ty(&item_cx, hir_ty)
392 pub fn hir_trait_to_predicates<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, hir_trait: &hir::TraitRef)
393 -> (ty::PolyTraitRef<'tcx>, Vec<(ty::PolyProjectionPredicate<'tcx>, Span)>) {
394 // In case there are any projections etc, find the "environment"
395 // def-id that will be used to determine the traits/predicates in
396 // scope. This is derived from the enclosing item-like thing.
397 let env_hir_id = tcx.hir().get_parent_item(hir_trait.hir_ref_id);
398 let env_def_id = tcx.hir().local_def_id_from_hir_id(env_hir_id);
399 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id);
400 let mut projections = Vec::new();
401 let (principal, _) = astconv::AstConv::instantiate_poly_trait_ref_inner(
402 &item_cx, hir_trait, tcx.types.err, &mut projections, true
405 (principal, projections)
408 __build_diagnostic_array! { librustc_typeck, DIAGNOSTICS }