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)]
70 #![feature(inner_deref)]
73 #![recursion_limit="256"]
75 #[macro_use] extern crate log;
76 #[macro_use] extern crate syntax;
78 #[macro_use] extern crate rustc;
87 mod constrained_generic_params;
88 mod structured_errors;
94 use rustc_target::spec::abi::Abi;
95 use rustc::hir::{self, Node};
96 use rustc::hir::def_id::{DefId, LOCAL_CRATE};
97 use rustc::infer::InferOk;
101 use rustc::util::common::ErrorReported;
102 use rustc::session::config::EntryFnType;
103 use rustc::traits::{ObligationCause, ObligationCauseCode, TraitEngine, TraitEngineExt};
104 use rustc::ty::subst::SubstsRef;
105 use rustc::ty::{self, Ty, TyCtxt};
106 use rustc::ty::query::Providers;
108 use syntax_pos::{DUMMY_SP, Span};
109 use util::common::time;
113 use astconv::{AstConv, Bounds};
114 pub use collect::checked_type_of;
116 pub struct TypeAndSubsts<'tcx> {
117 substs: SubstsRef<'tcx>,
121 fn require_c_abi_if_c_variadic(tcx: TyCtxt<'_>, decl: &hir::FnDecl, abi: Abi, span: Span) {
122 if decl.c_variadic && !(abi == Abi::C || abi == Abi::Cdecl) {
123 let mut err = struct_span_err!(tcx.sess, span, E0045,
124 "C-variadic function must have C or cdecl calling convention");
125 err.span_label(span, "C-variadics require C or cdecl calling convention").emit();
129 fn require_same_types<'tcx>(
131 cause: &ObligationCause<'tcx>,
135 tcx.infer_ctxt().enter(|ref infcx| {
136 let param_env = ty::ParamEnv::empty();
137 let mut fulfill_cx = TraitEngine::new(infcx.tcx);
138 match infcx.at(&cause, param_env).eq(expected, actual) {
139 Ok(InferOk { obligations, .. }) => {
140 fulfill_cx.register_predicate_obligations(infcx, obligations);
143 infcx.report_mismatched_types(cause, expected, actual, err).emit();
148 match fulfill_cx.select_all_or_error(infcx) {
151 infcx.report_fulfillment_errors(&errors, None, false);
158 fn check_main_fn_ty(tcx: TyCtxt<'_>, main_def_id: DefId) {
159 let main_id = tcx.hir().as_local_hir_id(main_def_id).unwrap();
160 let main_span = tcx.def_span(main_def_id);
161 let main_t = tcx.type_of(main_def_id);
164 if let Some(Node::Item(it)) = tcx.hir().find(main_id) {
165 if let hir::ItemKind::Fn(.., ref generics, _) = it.node {
166 let mut error = false;
167 if !generics.params.is_empty() {
168 let msg = "`main` function is not allowed to have generic \
169 parameters".to_owned();
170 let label = "`main` cannot have generic parameters".to_string();
171 struct_span_err!(tcx.sess, generics.span, E0131, "{}", msg)
172 .span_label(generics.span, label)
176 if let Some(sp) = generics.where_clause.span() {
177 struct_span_err!(tcx.sess, sp, E0646,
178 "`main` function is not allowed to have a `where` clause")
179 .span_label(sp, "`main` cannot have a `where` clause")
189 let actual = tcx.fn_sig(main_def_id);
190 let expected_return_type = if tcx.lang_items().termination().is_some() {
191 // we take the return type of the given main function, the real check is done
193 actual.output().skip_binder()
195 // standard () main return type
199 let se_ty = tcx.mk_fn_ptr(ty::Binder::bind(
202 expected_return_type,
204 hir::Unsafety::Normal,
211 &ObligationCause::new(main_span, main_id, ObligationCauseCode::MainFunctionType),
213 tcx.mk_fn_ptr(actual));
217 "main has a non-function type: found `{}`",
223 fn check_start_fn_ty(tcx: TyCtxt<'_>, start_def_id: DefId) {
224 let start_id = tcx.hir().as_local_hir_id(start_def_id).unwrap();
225 let start_span = tcx.def_span(start_def_id);
226 let start_t = tcx.type_of(start_def_id);
229 if let Some(Node::Item(it)) = tcx.hir().find(start_id) {
230 if let hir::ItemKind::Fn(.., ref generics, _) = it.node {
231 let mut error = false;
232 if !generics.params.is_empty() {
233 struct_span_err!(tcx.sess, generics.span, E0132,
234 "start function is not allowed to have type parameters")
235 .span_label(generics.span,
236 "start function cannot have type parameters")
240 if let Some(sp) = generics.where_clause.span() {
241 struct_span_err!(tcx.sess, sp, E0647,
242 "start function is not allowed to have a `where` clause")
243 .span_label(sp, "start function cannot have a `where` clause")
253 let se_ty = tcx.mk_fn_ptr(ty::Binder::bind(
257 tcx.mk_imm_ptr(tcx.mk_imm_ptr(tcx.types.u8))
261 hir::Unsafety::Normal,
268 &ObligationCause::new(start_span, start_id, ObligationCauseCode::StartFunctionType),
270 tcx.mk_fn_ptr(tcx.fn_sig(start_def_id)));
273 span_bug!(start_span,
274 "start has a non-function type: found `{}`",
280 fn check_for_entry_fn(tcx: TyCtxt<'_>) {
281 match tcx.entry_fn(LOCAL_CRATE) {
282 Some((def_id, EntryFnType::Main)) => check_main_fn_ty(tcx, def_id),
283 Some((def_id, EntryFnType::Start)) => check_start_fn_ty(tcx, def_id),
288 pub fn provide(providers: &mut Providers<'_>) {
289 collect::provide(providers);
290 coherence::provide(providers);
291 check::provide(providers);
292 variance::provide(providers);
293 outlives::provide(providers);
294 impl_wf_check::provide(providers);
297 pub fn check_crate(tcx: TyCtxt<'_>) -> Result<(), ErrorReported> {
298 tcx.sess.profiler(|p| p.start_activity("type-check crate"));
300 // this ensures that later parts of type checking can assume that items
301 // have valid types and not error
302 // FIXME(matthewjasper) We shouldn't need to do this.
303 tcx.sess.track_errors(|| {
304 time(tcx.sess, "type collecting", || {
305 for &module in tcx.hir().krate().modules.keys() {
306 tcx.ensure().collect_mod_item_types(tcx.hir().local_def_id(module));
311 if tcx.features().rustc_attrs {
312 tcx.sess.track_errors(|| {
313 time(tcx.sess, "outlives testing", ||
314 outlives::test::test_inferred_outlives(tcx));
318 tcx.sess.track_errors(|| {
319 time(tcx.sess, "impl wf inference", ||
320 impl_wf_check::impl_wf_check(tcx));
323 tcx.sess.track_errors(|| {
324 time(tcx.sess, "coherence checking", ||
325 coherence::check_coherence(tcx));
328 if tcx.features().rustc_attrs {
329 tcx.sess.track_errors(|| {
330 time(tcx.sess, "variance testing", ||
331 variance::test::test_variance(tcx));
335 tcx.sess.track_errors(|| {
336 time(tcx.sess, "wf checking", || check::check_wf_new(tcx));
339 time(tcx.sess, "item-types checking", || {
340 for &module in tcx.hir().krate().modules.keys() {
341 tcx.ensure().check_mod_item_types(tcx.hir().local_def_id(module));
345 time(tcx.sess, "item-bodies checking", || tcx.typeck_item_bodies(LOCAL_CRATE));
347 check_unused::check_crate(tcx);
348 check_for_entry_fn(tcx);
350 tcx.sess.profiler(|p| p.end_activity("type-check crate"));
352 if tcx.sess.err_count() == 0 {
359 /// A quasi-deprecated helper used in rustdoc and clippy to get
360 /// the type from a HIR node.
361 pub fn hir_ty_to_ty<'tcx>(tcx: TyCtxt<'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_item(hir_ty.hir_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);
369 astconv::AstConv::ast_ty_to_ty(&item_cx, hir_ty)
372 pub fn hir_trait_to_predicates<'tcx>(
374 hir_trait: &hir::TraitRef,
376 // In case there are any projections, etc., find the "environment"
377 // def-ID that will be used to determine the traits/predicates in
378 // scope. This is derived from the enclosing item-like thing.
379 let env_hir_id = tcx.hir().get_parent_item(hir_trait.hir_ref_id);
380 let env_def_id = tcx.hir().local_def_id(env_hir_id);
381 let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id);
382 let mut bounds = Bounds::default();
383 let _ = AstConv::instantiate_poly_trait_ref_inner(
384 &item_cx, hir_trait, DUMMY_SP, tcx.types.err, &mut bounds, true