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/")]
73 #![allow(non_camel_case_types)]
75 #![feature(advanced_slice_patterns)]
76 #![feature(box_patterns)]
77 #![feature(box_syntax)]
78 #![feature(conservative_impl_trait)]
79 #![feature(copy_closures, clone_closures)]
80 #![feature(crate_visibility_modifier)]
82 #![feature(match_default_bindings)]
83 #![feature(never_type)]
84 #![feature(option_filter)]
86 #![feature(refcell_replace_swap)]
87 #![feature(rustc_diagnostic_macros)]
88 #![feature(slice_patterns)]
89 #![feature(i128_type)]
91 #[macro_use] extern crate log;
92 #[macro_use] extern crate syntax;
93 extern crate syntax_pos;
96 #[macro_use] extern crate rustc;
97 extern crate rustc_platform_intrinsics as intrinsics;
98 extern crate rustc_const_math;
99 extern crate rustc_data_structures;
100 extern crate rustc_errors as errors;
108 use hir::map as hir_map;
109 use rustc::infer::InferOk;
110 use rustc::ty::subst::Substs;
111 use rustc::ty::{self, Ty, TyCtxt};
112 use rustc::ty::maps::Providers;
113 use rustc::traits::{FulfillmentContext, ObligationCause, ObligationCauseCode, Reveal};
114 use session::{CompileIncomplete, config};
115 use util::common::time;
118 use syntax::abi::Abi;
119 use syntax_pos::Span;
123 // NB: This module needs to be declared first so diagnostics are
124 // registered before they are used.
132 mod constrained_type_params;
133 mod structured_errors;
139 pub struct TypeAndSubsts<'tcx> {
140 substs: &'tcx Substs<'tcx>,
144 fn require_c_abi_if_variadic(tcx: TyCtxt,
148 if decl.variadic && !(abi == Abi::C || abi == Abi::Cdecl) {
149 let mut err = struct_span_err!(tcx.sess, span, E0045,
150 "variadic function must have C or cdecl calling convention");
151 err.span_label(span, "variadics require C or cdecl calling convention").emit();
155 fn require_same_types<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
156 cause: &ObligationCause<'tcx>,
160 tcx.infer_ctxt().enter(|ref infcx| {
161 let param_env = ty::ParamEnv::empty(Reveal::UserFacing);
162 let mut fulfill_cx = FulfillmentContext::new();
163 match infcx.at(&cause, param_env).eq(expected, actual) {
164 Ok(InferOk { obligations, .. }) => {
165 fulfill_cx.register_predicate_obligations(infcx, obligations);
168 infcx.report_mismatched_types(cause, expected, actual, err).emit();
173 match fulfill_cx.select_all_or_error(infcx) {
176 infcx.report_fulfillment_errors(&errors, None);
183 fn check_main_fn_ty<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
184 main_id: ast::NodeId,
186 let main_def_id = tcx.hir.local_def_id(main_id);
187 let main_t = tcx.type_of(main_def_id);
190 match tcx.hir.find(main_id) {
191 Some(hir_map::NodeItem(it)) => {
193 hir::ItemFn(.., ref generics, _) => {
194 if !generics.params.is_empty() {
195 struct_span_err!(tcx.sess, generics.span, E0131,
196 "main function is not allowed to have type parameters")
197 .span_label(generics.span,
198 "main cannot have type parameters")
209 let actual = tcx.fn_sig(main_def_id);
210 let expected_return_type = if tcx.lang_items().termination().is_some()
211 && tcx.features().termination_trait {
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(
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>,
245 start_id: ast::NodeId,
247 let start_def_id = tcx.hir.local_def_id(start_id);
248 let start_t = tcx.type_of(start_def_id);
251 match tcx.hir.find(start_id) {
252 Some(hir_map::NodeItem(it)) => {
254 hir::ItemFn(..,ref ps,_)
255 if !ps.params.is_empty() => {
256 struct_span_err!(tcx.sess, ps.span, E0132,
257 "start function is not allowed to have type parameters")
259 "start function cannot have type parameters")
269 let se_ty = tcx.mk_fn_ptr(ty::Binder(
273 tcx.mk_imm_ptr(tcx.mk_imm_ptr(tcx.types.u8))
277 hir::Unsafety::Normal,
284 &ObligationCause::new(start_span, start_id, ObligationCauseCode::StartFunctionType),
286 tcx.mk_fn_ptr(tcx.fn_sig(start_def_id)));
289 span_bug!(start_span,
290 "start has a non-function type: found `{}`",
296 fn check_for_entry_fn<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
297 if let Some((id, sp)) = *tcx.sess.entry_fn.borrow() {
298 match tcx.sess.entry_type.get() {
299 Some(config::EntryMain) => check_main_fn_ty(tcx, id, sp),
300 Some(config::EntryStart) => check_start_fn_ty(tcx, id, sp),
301 Some(config::EntryNone) => {}
302 None => bug!("entry function without a type")
307 pub fn provide(providers: &mut Providers) {
308 collect::provide(providers);
309 coherence::provide(providers);
310 check::provide(providers);
311 variance::provide(providers);
312 outlives::provide(providers);
315 pub fn check_crate<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>)
316 -> Result<(), CompileIncomplete>
318 // this ensures that later parts of type checking can assume that items
319 // have valid types and not error
320 tcx.sess.track_errors(|| {
321 time(tcx.sess, "type collecting", ||
322 collect::collect_item_types(tcx));
326 tcx.sess.track_errors(|| {
327 time(tcx.sess, "outlives testing", ||
328 outlives::test::test_inferred_outlives(tcx));
331 tcx.sess.track_errors(|| {
332 time(tcx.sess, "impl wf inference", ||
333 impl_wf_check::impl_wf_check(tcx));
336 tcx.sess.track_errors(|| {
337 time(tcx.sess, "coherence checking", ||
338 coherence::check_coherence(tcx));
341 tcx.sess.track_errors(|| {
342 time(tcx.sess, "variance testing", ||
343 variance::test::test_variance(tcx));
346 time(tcx.sess, "wf checking", || check::check_wf_new(tcx))?;
348 time(tcx.sess, "item-types checking", || check::check_item_types(tcx))?;
350 time(tcx.sess, "item-bodies checking", || check::check_item_bodies(tcx))?;
352 check_unused::check_crate(tcx);
353 check_for_entry_fn(tcx);
355 tcx.sess.compile_status()
358 /// A quasi-deprecated helper used in rustdoc and save-analysis to get
359 /// the type from a HIR node.
360 pub fn hir_ty_to_ty<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, '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(hir_ty.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);
367 astconv::AstConv::ast_ty_to_ty(&item_cx, hir_ty)
370 pub fn hir_trait_to_predicates<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, hir_trait: &hir::TraitRef)
371 -> (ty::PolyTraitRef<'tcx>, Vec<ty::PolyProjectionPredicate<'tcx>>) {
372 // In case there are any projections etc, find the "environment"
373 // def-id that will be used to determine the traits/predicates in
374 // scope. This is derived from the enclosing item-like thing.
375 let env_node_id = tcx.hir.get_parent(hir_trait.ref_id);
376 let env_def_id = tcx.hir.local_def_id(env_node_id);
377 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id);
378 let mut projections = Vec::new();
379 let principal = astconv::AstConv::instantiate_poly_trait_ref_inner(
380 &item_cx, hir_trait, tcx.types.err, &mut projections, true
382 (principal, projections)
385 __build_diagnostic_array! { librustc_typeck, DIAGNOSTICS }