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)]
66 #![feature(in_band_lifetimes)]
68 #![feature(slice_patterns)]
69 #![feature(never_type)]
71 #![recursion_limit="256"]
73 #[macro_use] extern crate log;
74 #[macro_use] extern crate syntax;
76 #[macro_use] extern crate rustc;
83 mod constrained_generic_params;
84 mod structured_errors;
90 use rustc_target::spec::abi::Abi;
91 use rustc::hir::{self, Node};
92 use rustc::hir::def_id::{DefId, LOCAL_CRATE};
93 use rustc::infer::InferOk;
97 use rustc::util::common::ErrorReported;
98 use rustc::session::config::EntryFnType;
99 use rustc::traits::{ObligationCause, ObligationCauseCode, TraitEngine, TraitEngineExt};
100 use rustc::ty::subst::SubstsRef;
101 use rustc::ty::{self, Ty, TyCtxt};
102 use rustc::ty::query::Providers;
104 use syntax_pos::{DUMMY_SP, Span};
105 use util::common::time;
107 use rustc_error_codes::*;
111 use astconv::{AstConv, Bounds};
112 pub struct TypeAndSubsts<'tcx> {
113 substs: SubstsRef<'tcx>,
117 fn require_c_abi_if_c_variadic(tcx: TyCtxt<'_>, decl: &hir::FnDecl, abi: Abi, span: Span) {
118 if decl.c_variadic && !(abi == Abi::C || abi == Abi::Cdecl) {
119 let mut err = struct_span_err!(tcx.sess, span, E0045,
120 "C-variadic function must have C or cdecl calling convention");
121 err.span_label(span, "C-variadics require C or cdecl calling convention").emit();
125 fn require_same_types<'tcx>(
127 cause: &ObligationCause<'tcx>,
131 tcx.infer_ctxt().enter(|ref infcx| {
132 let param_env = ty::ParamEnv::empty();
133 let mut fulfill_cx = TraitEngine::new(infcx.tcx);
134 match infcx.at(&cause, param_env).eq(expected, actual) {
135 Ok(InferOk { obligations, .. }) => {
136 fulfill_cx.register_predicate_obligations(infcx, obligations);
139 infcx.report_mismatched_types(cause, expected, actual, err).emit();
144 match fulfill_cx.select_all_or_error(infcx) {
147 infcx.report_fulfillment_errors(&errors, None, false);
154 fn check_main_fn_ty(tcx: TyCtxt<'_>, main_def_id: DefId) {
155 let main_id = tcx.hir().as_local_hir_id(main_def_id).unwrap();
156 let main_span = tcx.def_span(main_def_id);
157 let main_t = tcx.type_of(main_def_id);
160 if let Some(Node::Item(it)) = tcx.hir().find(main_id) {
161 if let hir::ItemKind::Fn(.., ref generics, _) = it.kind {
162 let mut error = false;
163 if !generics.params.is_empty() {
164 let msg = "`main` function is not allowed to have generic \
165 parameters".to_owned();
166 let label = "`main` cannot have generic parameters".to_string();
167 struct_span_err!(tcx.sess, generics.span, E0131, "{}", msg)
168 .span_label(generics.span, label)
172 if let Some(sp) = generics.where_clause.span() {
173 struct_span_err!(tcx.sess, sp, E0646,
174 "`main` function is not allowed to have a `where` clause")
175 .span_label(sp, "`main` cannot have a `where` clause")
185 let actual = tcx.fn_sig(main_def_id);
186 let expected_return_type = if tcx.lang_items().termination().is_some() {
187 // we take the return type of the given main function, the real check is done
189 actual.output().skip_binder()
191 // standard () main return type
195 let se_ty = tcx.mk_fn_ptr(ty::Binder::bind(
198 expected_return_type,
200 hir::Unsafety::Normal,
207 &ObligationCause::new(main_span, main_id, ObligationCauseCode::MainFunctionType),
209 tcx.mk_fn_ptr(actual));
213 "main has a non-function type: found `{}`",
219 fn check_start_fn_ty(tcx: TyCtxt<'_>, start_def_id: DefId) {
220 let start_id = tcx.hir().as_local_hir_id(start_def_id).unwrap();
221 let start_span = tcx.def_span(start_def_id);
222 let start_t = tcx.type_of(start_def_id);
225 if let Some(Node::Item(it)) = tcx.hir().find(start_id) {
226 if let hir::ItemKind::Fn(.., ref generics, _) = it.kind {
227 let mut error = false;
228 if !generics.params.is_empty() {
229 struct_span_err!(tcx.sess, generics.span, E0132,
230 "start function is not allowed to have type parameters")
231 .span_label(generics.span,
232 "start function cannot have type parameters")
236 if let Some(sp) = generics.where_clause.span() {
237 struct_span_err!(tcx.sess, sp, E0647,
238 "start function is not allowed to have a `where` clause")
239 .span_label(sp, "start function cannot have a `where` clause")
249 let se_ty = tcx.mk_fn_ptr(ty::Binder::bind(
253 tcx.mk_imm_ptr(tcx.mk_imm_ptr(tcx.types.u8))
257 hir::Unsafety::Normal,
264 &ObligationCause::new(start_span, start_id, ObligationCauseCode::StartFunctionType),
266 tcx.mk_fn_ptr(tcx.fn_sig(start_def_id)));
269 span_bug!(start_span,
270 "start has a non-function type: found `{}`",
276 fn check_for_entry_fn(tcx: TyCtxt<'_>) {
277 match tcx.entry_fn(LOCAL_CRATE) {
278 Some((def_id, EntryFnType::Main)) => check_main_fn_ty(tcx, def_id),
279 Some((def_id, EntryFnType::Start)) => check_start_fn_ty(tcx, def_id),
284 pub fn provide(providers: &mut Providers<'_>) {
285 collect::provide(providers);
286 coherence::provide(providers);
287 check::provide(providers);
288 variance::provide(providers);
289 outlives::provide(providers);
290 impl_wf_check::provide(providers);
293 pub fn check_crate(tcx: TyCtxt<'_>) -> Result<(), ErrorReported> {
294 let _prof_timer = tcx.prof.generic_activity("type_check_crate");
296 // this ensures that later parts of type checking can assume that items
297 // have valid types and not error
298 // FIXME(matthewjasper) We shouldn't need to do this.
299 tcx.sess.track_errors(|| {
300 time(tcx.sess, "type collecting", || {
301 for &module in tcx.hir().krate().modules.keys() {
302 tcx.ensure().collect_mod_item_types(tcx.hir().local_def_id(module));
307 if tcx.features().rustc_attrs {
308 tcx.sess.track_errors(|| {
309 time(tcx.sess, "outlives testing", ||
310 outlives::test::test_inferred_outlives(tcx));
314 tcx.sess.track_errors(|| {
315 time(tcx.sess, "impl wf inference", ||
316 impl_wf_check::impl_wf_check(tcx));
319 tcx.sess.track_errors(|| {
320 time(tcx.sess, "coherence checking", ||
321 coherence::check_coherence(tcx));
324 if tcx.features().rustc_attrs {
325 tcx.sess.track_errors(|| {
326 time(tcx.sess, "variance testing", ||
327 variance::test::test_variance(tcx));
331 tcx.sess.track_errors(|| {
332 time(tcx.sess, "wf checking", || check::check_wf_new(tcx));
335 time(tcx.sess, "item-types checking", || {
336 for &module in tcx.hir().krate().modules.keys() {
337 tcx.ensure().check_mod_item_types(tcx.hir().local_def_id(module));
341 time(tcx.sess, "item-bodies checking", || tcx.typeck_item_bodies(LOCAL_CRATE));
343 check_unused::check_crate(tcx);
344 check_for_entry_fn(tcx);
346 if tcx.sess.err_count() == 0 {
353 /// A quasi-deprecated helper used in rustdoc and clippy to get
354 /// the type from a HIR node.
355 pub fn hir_ty_to_ty<'tcx>(tcx: TyCtxt<'tcx>, hir_ty: &hir::Ty) -> Ty<'tcx> {
356 // In case there are any projections, etc., find the "environment"
357 // def-ID that will be used to determine the traits/predicates in
358 // scope. This is derived from the enclosing item-like thing.
359 let env_node_id = tcx.hir().get_parent_item(hir_ty.hir_id);
360 let env_def_id = tcx.hir().local_def_id(env_node_id);
361 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id);
363 astconv::AstConv::ast_ty_to_ty(&item_cx, hir_ty)
366 pub fn hir_trait_to_predicates<'tcx>(
368 hir_trait: &hir::TraitRef,
370 // In case there are any projections, etc., find the "environment"
371 // def-ID that will be used to determine the traits/predicates in
372 // scope. This is derived from the enclosing item-like thing.
373 let env_hir_id = tcx.hir().get_parent_item(hir_trait.hir_ref_id);
374 let env_def_id = tcx.hir().local_def_id(env_hir_id);
375 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id);
376 let mut bounds = Bounds::default();
377 let _ = AstConv::instantiate_poly_trait_ref_inner(
378 &item_cx, hir_trait, DUMMY_SP, tcx.types.err, &mut bounds, true