1 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
13 typeck.rs, an introduction
15 The type checker is responsible for:
17 1. Determining the type of each expression
18 2. Resolving methods and traits
19 3. Guaranteeing that most type rules are met ("most?", you say, "why most?"
20 Well, dear reader, read on)
22 The main entry point is `check_crate()`. Type checking operates in
25 1. The collect phase first passes over all items and determines their
26 type, without examining their "innards".
28 2. Variance inference then runs to compute the variance of each parameter
30 3. Coherence checks for overlapping or orphaned impls
32 4. Finally, the check phase then checks function bodies and so forth.
33 Within the check phase, we check each function body one at a time
34 (bodies of function expressions are checked as part of the
35 containing function). Inference is used to supply types wherever
36 they are unknown. The actual checking of a function itself has
37 several phases (check, regionck, writeback), as discussed in the
38 documentation for the `check` module.
40 The type checker is defined into various submodules which are documented
43 - astconv: converts the AST representation of types
44 into the `ty` representation
46 - collect: computes the types of each top-level item and enters them into
47 the `tcx.types` table for later use
49 - coherence: enforces coherence rules, builds some tables
51 - variance: variance inference
53 - outlives: outlives inference
55 - check: walks over function bodies and type checks them, inferring types for
56 local variables, type parameters, etc as necessary.
58 - infer: finds the types to use for each type variable such that
59 all subtyping and assignment constraints are met. In essence, the check
60 module specifies the constraints, and the infer module solves them.
64 This API is completely unstable and subject to change.
68 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
69 html_favicon_url = "https://doc.rust-lang.org/favicon.ico",
70 html_root_url = "https://doc.rust-lang.org/nightly/")]
72 #![allow(non_camel_case_types)]
74 #![cfg_attr(stage0, feature(dyn_trait))]
76 #![feature(box_patterns)]
77 #![feature(box_syntax)]
78 #![feature(crate_visibility_modifier)]
80 #![feature(exhaustive_patterns)]
82 #![feature(refcell_replace_swap)]
83 #![feature(rustc_diagnostic_macros)]
84 #![feature(slice_patterns)]
85 #![feature(slice_sort_by_cached_key)]
86 #![feature(never_type)]
88 #[macro_use] extern crate log;
89 #[macro_use] extern crate syntax;
90 extern crate syntax_pos;
93 #[macro_use] extern crate rustc;
94 extern crate rustc_platform_intrinsics as intrinsics;
95 extern crate rustc_const_math;
96 extern crate rustc_data_structures;
97 extern crate rustc_errors as errors;
98 extern crate rustc_target;
106 use hir::map as hir_map;
107 use rustc::infer::InferOk;
108 use rustc::ty::subst::Substs;
109 use rustc::ty::{self, Ty, TyCtxt};
110 use rustc::ty::maps::Providers;
111 use rustc::traits::{ObligationCause, ObligationCauseCode, TraitEngine};
112 use session::{CompileIncomplete, config};
113 use util::common::time;
116 use rustc_target::spec::abi::Abi;
117 use syntax_pos::Span;
121 // NB: This module needs to be declared first so diagnostics are
122 // registered before they are used.
130 mod constrained_type_params;
131 mod structured_errors;
137 pub struct TypeAndSubsts<'tcx> {
138 substs: &'tcx Substs<'tcx>,
142 fn require_c_abi_if_variadic(tcx: TyCtxt,
146 if decl.variadic && !(abi == Abi::C || abi == Abi::Cdecl) {
147 let mut err = struct_span_err!(tcx.sess, span, E0045,
148 "variadic function must have C or cdecl calling convention");
149 err.span_label(span, "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>,
182 main_id: ast::NodeId,
184 let main_def_id = tcx.hir.local_def_id(main_id);
185 let main_t = tcx.type_of(main_def_id);
188 match tcx.hir.find(main_id) {
189 Some(hir_map::NodeItem(it)) => {
191 hir::ItemFn(.., ref generics, _) => {
192 if !generics.params.is_empty() {
193 struct_span_err!(tcx.sess, generics.span, E0131,
194 "main function is not allowed to have type parameters")
195 .span_label(generics.span,
196 "main cannot have type parameters")
207 let actual = tcx.fn_sig(main_def_id);
208 let expected_return_type = if tcx.lang_items().termination().is_some() {
209 // we take the return type of the given main function, the real check is done
211 actual.output().skip_binder()
213 // standard () main return type
217 let se_ty = tcx.mk_fn_ptr(ty::Binder::bind(
220 expected_return_type,
222 hir::Unsafety::Normal,
229 &ObligationCause::new(main_span, main_id, ObligationCauseCode::MainFunctionType),
231 tcx.mk_fn_ptr(actual));
235 "main has a non-function type: found `{}`",
241 fn check_start_fn_ty<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
242 start_id: ast::NodeId,
244 let start_def_id = tcx.hir.local_def_id(start_id);
245 let start_t = tcx.type_of(start_def_id);
248 match tcx.hir.find(start_id) {
249 Some(hir_map::NodeItem(it)) => {
251 hir::ItemFn(..,ref ps,_)
252 if !ps.params.is_empty() => {
253 struct_span_err!(tcx.sess, ps.span, E0132,
254 "start function is not allowed to have type parameters")
256 "start function cannot have type parameters")
266 let se_ty = tcx.mk_fn_ptr(ty::Binder::bind(
270 tcx.mk_imm_ptr(tcx.mk_imm_ptr(tcx.types.u8))
274 hir::Unsafety::Normal,
281 &ObligationCause::new(start_span, start_id, ObligationCauseCode::StartFunctionType),
283 tcx.mk_fn_ptr(tcx.fn_sig(start_def_id)));
286 span_bug!(start_span,
287 "start has a non-function type: found `{}`",
293 fn check_for_entry_fn<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
294 if let Some((id, sp, entry_type)) = *tcx.sess.entry_fn.borrow() {
296 config::EntryMain => check_main_fn_ty(tcx, id, sp),
297 config::EntryStart => check_start_fn_ty(tcx, id, sp),
302 pub fn provide(providers: &mut Providers) {
303 collect::provide(providers);
304 coherence::provide(providers);
305 check::provide(providers);
306 variance::provide(providers);
307 outlives::provide(providers);
310 pub fn check_crate<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>)
311 -> Result<(), CompileIncomplete>
313 // this ensures that later parts of type checking can assume that items
314 // have valid types and not error
315 tcx.sess.track_errors(|| {
316 time(tcx.sess, "type collecting", ||
317 collect::collect_item_types(tcx));
321 tcx.sess.track_errors(|| {
322 time(tcx.sess, "outlives testing", ||
323 outlives::test::test_inferred_outlives(tcx));
326 tcx.sess.track_errors(|| {
327 time(tcx.sess, "impl wf inference", ||
328 impl_wf_check::impl_wf_check(tcx));
331 tcx.sess.track_errors(|| {
332 time(tcx.sess, "coherence checking", ||
333 coherence::check_coherence(tcx));
336 tcx.sess.track_errors(|| {
337 time(tcx.sess, "variance testing", ||
338 variance::test::test_variance(tcx));
341 time(tcx.sess, "wf checking", || check::check_wf_new(tcx))?;
343 time(tcx.sess, "item-types checking", || check::check_item_types(tcx))?;
345 time(tcx.sess, "item-bodies checking", || check::check_item_bodies(tcx))?;
347 check_unused::check_crate(tcx);
348 check_for_entry_fn(tcx);
350 tcx.sess.compile_status()
353 /// A quasi-deprecated helper used in rustdoc and save-analysis to get
354 /// the type from a HIR node.
355 pub fn hir_ty_to_ty<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, '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(hir_ty.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);
362 astconv::AstConv::ast_ty_to_ty(&item_cx, hir_ty)
365 pub fn hir_trait_to_predicates<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, hir_trait: &hir::TraitRef)
366 -> (ty::PolyTraitRef<'tcx>, Vec<ty::PolyProjectionPredicate<'tcx>>) {
367 // In case there are any projections etc, find the "environment"
368 // def-id that will be used to determine the traits/predicates in
369 // scope. This is derived from the enclosing item-like thing.
370 let env_node_id = tcx.hir.get_parent(hir_trait.ref_id);
371 let env_def_id = tcx.hir.local_def_id(env_node_id);
372 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id);
373 let mut projections = Vec::new();
374 let principal = astconv::AstConv::instantiate_poly_trait_ref_inner(
375 &item_cx, hir_trait, tcx.types.err, &mut projections, true
377 (principal, projections)
380 __build_diagnostic_array! { librustc_typeck, DIAGNOSTICS }