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(bool_to_option)]
63 #![feature(box_patterns)]
64 #![feature(box_syntax)]
65 #![feature(crate_visibility_modifier)]
66 #![feature(exhaustive_patterns)]
67 #![feature(in_band_lifetimes)]
69 #![feature(slice_patterns)]
70 #![feature(never_type)]
72 #![recursion_limit="256"]
74 #[macro_use] extern crate log;
75 #[macro_use] extern crate syntax;
77 #[macro_use] extern crate rustc;
79 // This is used by Clippy.
80 pub mod expr_use_visitor;
87 mod constrained_generic_params;
88 mod structured_errors;
90 mod mem_categorization;
95 use rustc_target::spec::abi::Abi;
96 use rustc::hir::{self, Node};
97 use rustc::hir::def_id::{DefId, LOCAL_CRATE};
98 use rustc::infer::InferOk;
102 use rustc::util::common::ErrorReported;
103 use rustc::session::config::EntryFnType;
104 use rustc::traits::{ObligationCause, ObligationCauseCode, TraitEngine, TraitEngineExt};
105 use rustc::ty::subst::SubstsRef;
106 use rustc::ty::{self, Ty, TyCtxt};
107 use rustc::ty::query::Providers;
109 use syntax_pos::{DUMMY_SP, Span};
110 use util::common::time;
112 use rustc_error_codes::*;
116 use astconv::{AstConv, Bounds};
117 pub struct TypeAndSubsts<'tcx> {
118 substs: SubstsRef<'tcx>,
122 fn require_c_abi_if_c_variadic(tcx: TyCtxt<'_>, decl: &hir::FnDecl, abi: Abi, span: Span) {
123 if decl.c_variadic && !(abi == Abi::C || abi == Abi::Cdecl) {
124 let mut err = struct_span_err!(tcx.sess, span, E0045,
125 "C-variadic function must have C or cdecl calling convention");
126 err.span_label(span, "C-variadics require C or cdecl calling convention").emit();
130 fn require_same_types<'tcx>(
132 cause: &ObligationCause<'tcx>,
136 tcx.infer_ctxt().enter(|ref infcx| {
137 let param_env = ty::ParamEnv::empty();
138 let mut fulfill_cx = TraitEngine::new(infcx.tcx);
139 match infcx.at(&cause, param_env).eq(expected, actual) {
140 Ok(InferOk { obligations, .. }) => {
141 fulfill_cx.register_predicate_obligations(infcx, obligations);
144 infcx.report_mismatched_types(cause, expected, actual, err).emit();
149 match fulfill_cx.select_all_or_error(infcx) {
152 infcx.report_fulfillment_errors(&errors, None, false);
159 fn check_main_fn_ty(tcx: TyCtxt<'_>, main_def_id: DefId) {
160 let main_id = tcx.hir().as_local_hir_id(main_def_id).unwrap();
161 let main_span = tcx.def_span(main_def_id);
162 let main_t = tcx.type_of(main_def_id);
165 if let Some(Node::Item(it)) = tcx.hir().find(main_id) {
166 if let hir::ItemKind::Fn(.., ref generics, _) = it.kind {
167 let mut error = false;
168 if !generics.params.is_empty() {
169 let msg = "`main` function is not allowed to have generic \
170 parameters".to_owned();
171 let label = "`main` cannot have generic parameters".to_string();
172 struct_span_err!(tcx.sess, generics.span, E0131, "{}", msg)
173 .span_label(generics.span, label)
177 if let Some(sp) = generics.where_clause.span() {
178 struct_span_err!(tcx.sess, sp, E0646,
179 "`main` function is not allowed to have a `where` clause")
180 .span_label(sp, "`main` cannot have a `where` clause")
190 let actual = tcx.fn_sig(main_def_id);
191 let expected_return_type = if tcx.lang_items().termination().is_some() {
192 // we take the return type of the given main function, the real check is done
194 actual.output().skip_binder()
196 // standard () main return type
200 let se_ty = tcx.mk_fn_ptr(ty::Binder::bind(
203 expected_return_type,
205 hir::Unsafety::Normal,
212 &ObligationCause::new(main_span, main_id, ObligationCauseCode::MainFunctionType),
214 tcx.mk_fn_ptr(actual));
218 "main has a non-function type: found `{}`",
224 fn check_start_fn_ty(tcx: TyCtxt<'_>, start_def_id: DefId) {
225 let start_id = tcx.hir().as_local_hir_id(start_def_id).unwrap();
226 let start_span = tcx.def_span(start_def_id);
227 let start_t = tcx.type_of(start_def_id);
230 if let Some(Node::Item(it)) = tcx.hir().find(start_id) {
231 if let hir::ItemKind::Fn(.., ref generics, _) = it.kind {
232 let mut error = false;
233 if !generics.params.is_empty() {
234 struct_span_err!(tcx.sess, generics.span, E0132,
235 "start function is not allowed to have type parameters")
236 .span_label(generics.span,
237 "start function cannot have type parameters")
241 if let Some(sp) = generics.where_clause.span() {
242 struct_span_err!(tcx.sess, sp, E0647,
243 "start function is not allowed to have a `where` clause")
244 .span_label(sp, "start function cannot have a `where` clause")
254 let se_ty = tcx.mk_fn_ptr(ty::Binder::bind(
258 tcx.mk_imm_ptr(tcx.mk_imm_ptr(tcx.types.u8))
262 hir::Unsafety::Normal,
269 &ObligationCause::new(start_span, start_id, ObligationCauseCode::StartFunctionType),
271 tcx.mk_fn_ptr(tcx.fn_sig(start_def_id)));
274 span_bug!(start_span,
275 "start has a non-function type: found `{}`",
281 fn check_for_entry_fn(tcx: TyCtxt<'_>) {
282 match tcx.entry_fn(LOCAL_CRATE) {
283 Some((def_id, EntryFnType::Main)) => check_main_fn_ty(tcx, def_id),
284 Some((def_id, EntryFnType::Start)) => check_start_fn_ty(tcx, def_id),
289 pub fn provide(providers: &mut Providers<'_>) {
290 collect::provide(providers);
291 coherence::provide(providers);
292 check::provide(providers);
293 variance::provide(providers);
294 outlives::provide(providers);
295 impl_wf_check::provide(providers);
298 pub fn check_crate(tcx: TyCtxt<'_>) -> Result<(), ErrorReported> {
299 let _prof_timer = tcx.prof.generic_activity("type_check_crate");
301 // this ensures that later parts of type checking can assume that items
302 // have valid types and not error
303 // FIXME(matthewjasper) We shouldn't need to do this.
304 tcx.sess.track_errors(|| {
305 time(tcx.sess, "type collecting", || {
306 for &module in tcx.hir().krate().modules.keys() {
307 tcx.ensure().collect_mod_item_types(tcx.hir().local_def_id(module));
312 if tcx.features().rustc_attrs {
313 tcx.sess.track_errors(|| {
314 time(tcx.sess, "outlives testing", ||
315 outlives::test::test_inferred_outlives(tcx));
319 tcx.sess.track_errors(|| {
320 time(tcx.sess, "impl wf inference", ||
321 impl_wf_check::impl_wf_check(tcx));
324 tcx.sess.track_errors(|| {
325 time(tcx.sess, "coherence checking", ||
326 coherence::check_coherence(tcx));
329 if tcx.features().rustc_attrs {
330 tcx.sess.track_errors(|| {
331 time(tcx.sess, "variance testing", ||
332 variance::test::test_variance(tcx));
336 tcx.sess.track_errors(|| {
337 time(tcx.sess, "wf checking", || check::check_wf_new(tcx));
340 time(tcx.sess, "item-types checking", || {
341 for &module in tcx.hir().krate().modules.keys() {
342 tcx.ensure().check_mod_item_types(tcx.hir().local_def_id(module));
346 time(tcx.sess, "item-bodies checking", || tcx.typeck_item_bodies(LOCAL_CRATE));
348 check_unused::check_crate(tcx);
349 check_for_entry_fn(tcx);
351 if tcx.sess.err_count() == 0 {
358 /// A quasi-deprecated helper used in rustdoc and clippy to get
359 /// the type from a HIR node.
360 pub fn hir_ty_to_ty<'tcx>(tcx: TyCtxt<'tcx>, hir_ty: &hir::Ty) -> Ty<'tcx> {
361 // In case there are any projections, etc., find the "environment"
362 // def-ID that will be used to determine the traits/predicates in
363 // scope. This is derived from the enclosing item-like thing.
364 let env_node_id = tcx.hir().get_parent_item(hir_ty.hir_id);
365 let env_def_id = tcx.hir().local_def_id(env_node_id);
366 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id);
368 astconv::AstConv::ast_ty_to_ty(&item_cx, hir_ty)
371 pub fn hir_trait_to_predicates<'tcx>(
373 hir_trait: &hir::TraitRef,
375 // In case there are any projections, etc., find the "environment"
376 // def-ID that will be used to determine the traits/predicates in
377 // scope. This is derived from the enclosing item-like thing.
378 let env_hir_id = tcx.hir().get_parent_item(hir_trait.hir_ref_id);
379 let env_def_id = tcx.hir().local_def_id(env_hir_id);
380 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id);
381 let mut bounds = Bounds::default();
382 let _ = AstConv::instantiate_poly_trait_ref_inner(
383 &item_cx, hir_trait, DUMMY_SP, tcx.types.err, &mut bounds, true