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)]
90 #[macro_use] extern crate log;
91 #[macro_use] extern crate syntax;
92 extern crate syntax_pos;
95 #[macro_use] extern crate rustc;
96 extern crate rustc_platform_intrinsics as intrinsics;
97 extern crate rustc_const_math;
98 extern crate rustc_data_structures;
99 extern crate rustc_errors as errors;
107 use hir::map as hir_map;
108 use rustc::infer::InferOk;
109 use rustc::ty::subst::Substs;
110 use rustc::ty::{self, Ty, TyCtxt};
111 use rustc::ty::maps::Providers;
112 use rustc::traits::{FulfillmentContext, ObligationCause, ObligationCauseCode, Reveal};
113 use session::{CompileIncomplete, config};
114 use util::common::time;
117 use syntax::abi::Abi;
118 use syntax_pos::Span;
122 // NB: This module needs to be declared first so diagnostics are
123 // registered before they are used.
131 mod constrained_type_params;
132 mod structured_errors;
138 pub struct TypeAndSubsts<'tcx> {
139 substs: &'tcx Substs<'tcx>,
143 fn require_c_abi_if_variadic(tcx: TyCtxt,
147 if decl.variadic && !(abi == Abi::C || abi == Abi::Cdecl) {
148 let mut err = struct_span_err!(tcx.sess, span, E0045,
149 "variadic function must have C or cdecl calling convention");
150 err.span_label(span, "variadics require C or cdecl calling convention").emit();
154 fn require_same_types<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
155 cause: &ObligationCause<'tcx>,
159 tcx.infer_ctxt().enter(|ref infcx| {
160 let param_env = ty::ParamEnv::empty(Reveal::UserFacing);
161 let mut fulfill_cx = FulfillmentContext::new();
162 match infcx.at(&cause, param_env).eq(expected, actual) {
163 Ok(InferOk { obligations, .. }) => {
164 fulfill_cx.register_predicate_obligations(infcx, obligations);
167 infcx.report_mismatched_types(cause, expected, actual, err).emit();
172 match fulfill_cx.select_all_or_error(infcx) {
175 infcx.report_fulfillment_errors(&errors, None);
182 fn check_main_fn_ty<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
183 main_id: ast::NodeId,
185 let main_def_id = tcx.hir.local_def_id(main_id);
186 let main_t = tcx.type_of(main_def_id);
189 match tcx.hir.find(main_id) {
190 Some(hir_map::NodeItem(it)) => {
192 hir::ItemFn(.., ref generics, _) => {
193 if !generics.params.is_empty() {
194 struct_span_err!(tcx.sess, generics.span, E0131,
195 "main function is not allowed to have type parameters")
196 .span_label(generics.span,
197 "main cannot have type parameters")
208 let actual = tcx.fn_sig(main_def_id);
209 let expected_return_type = if tcx.lang_items().termination().is_some()
210 && tcx.sess.features.borrow().termination_trait {
211 // we take the return type of the given main function, the real check is done
213 actual.output().skip_binder()
215 // standard () main return type
219 let se_ty = tcx.mk_fn_ptr(ty::Binder(
222 expected_return_type,
224 hir::Unsafety::Normal,
231 &ObligationCause::new(main_span, main_id, ObligationCauseCode::MainFunctionType),
233 tcx.mk_fn_ptr(actual));
237 "main has a non-function type: found `{}`",
243 fn check_start_fn_ty<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
244 start_id: ast::NodeId,
246 let start_def_id = tcx.hir.local_def_id(start_id);
247 let start_t = tcx.type_of(start_def_id);
250 match tcx.hir.find(start_id) {
251 Some(hir_map::NodeItem(it)) => {
253 hir::ItemFn(..,ref ps,_)
254 if !ps.params.is_empty() => {
255 struct_span_err!(tcx.sess, ps.span, E0132,
256 "start function is not allowed to have type parameters")
258 "start function cannot have type parameters")
268 let se_ty = tcx.mk_fn_ptr(ty::Binder(
272 tcx.mk_imm_ptr(tcx.mk_imm_ptr(tcx.types.u8))
276 hir::Unsafety::Normal,
283 &ObligationCause::new(start_span, start_id, ObligationCauseCode::StartFunctionType),
285 tcx.mk_fn_ptr(tcx.fn_sig(start_def_id)));
288 span_bug!(start_span,
289 "start has a non-function type: found `{}`",
295 fn check_for_entry_fn<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
296 if let Some((id, sp)) = *tcx.sess.entry_fn.borrow() {
297 match tcx.sess.entry_type.get() {
298 Some(config::EntryMain) => check_main_fn_ty(tcx, id, sp),
299 Some(config::EntryStart) => check_start_fn_ty(tcx, id, sp),
300 Some(config::EntryNone) => {}
301 None => bug!("entry function without a type")
306 pub fn provide(providers: &mut Providers) {
307 collect::provide(providers);
308 coherence::provide(providers);
309 check::provide(providers);
310 variance::provide(providers);
311 outlives::provide(providers);
314 pub fn check_crate<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>)
315 -> Result<(), CompileIncomplete>
317 let time_passes = tcx.sess.time_passes();
319 // this ensures that later parts of type checking can assume that items
320 // have valid types and not error
321 tcx.sess.track_errors(|| {
322 time(time_passes, "type collecting", ||
323 collect::collect_item_types(tcx));
327 tcx.sess.track_errors(|| {
328 time(time_passes, "outlives testing", ||
329 outlives::test::test_inferred_outlives(tcx));
332 tcx.sess.track_errors(|| {
333 time(time_passes, "impl wf inference", ||
334 impl_wf_check::impl_wf_check(tcx));
337 tcx.sess.track_errors(|| {
338 time(time_passes, "coherence checking", ||
339 coherence::check_coherence(tcx));
342 tcx.sess.track_errors(|| {
343 time(time_passes, "variance testing", ||
344 variance::test::test_variance(tcx));
347 time(time_passes, "wf checking", || check::check_wf_new(tcx))?;
349 time(time_passes, "item-types checking", || check::check_item_types(tcx))?;
351 time(time_passes, "item-bodies checking", || check::check_item_bodies(tcx))?;
353 check_unused::check_crate(tcx);
354 check_for_entry_fn(tcx);
356 tcx.sess.compile_status()
359 /// A quasi-deprecated helper used in rustdoc and save-analysis to get
360 /// the type from a HIR node.
361 pub fn hir_ty_to_ty<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, hir_ty: &hir::Ty) -> Ty<'tcx> {
362 // In case there are any projections etc, find the "environment"
363 // def-id that will be used to determine the traits/predicates in
364 // scope. This is derived from the enclosing item-like thing.
365 let env_node_id = tcx.hir.get_parent(hir_ty.id);
366 let env_def_id = tcx.hir.local_def_id(env_node_id);
367 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<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, hir_trait: &hir::TraitRef)
372 -> (ty::PolyTraitRef<'tcx>, Vec<ty::PolyProjectionPredicate<'tcx>>) {
373 // In case there are any projections etc, find the "environment"
374 // def-id that will be used to determine the traits/predicates in
375 // scope. This is derived from the enclosing item-like thing.
376 let env_node_id = tcx.hir.get_parent(hir_trait.ref_id);
377 let env_def_id = tcx.hir.local_def_id(env_node_id);
378 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id);
379 let mut projections = Vec::new();
380 let principal = astconv::AstConv::instantiate_poly_trait_ref_inner(
381 &item_cx, hir_trait, tcx.types.err, &mut projections, true
383 (principal, projections)
386 __build_diagnostic_array! { librustc_typeck, DIAGNOSTICS }