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 // The job of the coherence phase of typechecking is to ensure that
14 // each trait has at most one implementation for each type. This is
15 // done by the orphan and overlap modules. Then we build up various
16 // mappings. That mapping code resides here.
18 use hir::def_id::{DefId, LOCAL_CRATE};
20 use rustc::ty::{self, TyCtxt, TypeFoldable};
21 use rustc::ty::query::Providers;
27 mod inherent_impls_overlap;
31 fn check_impl<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, node_id: ast::NodeId) {
32 let impl_def_id = tcx.hir().local_def_id(node_id);
34 // If there are no traits, then this implementation must have a
37 if let Some(trait_ref) = tcx.impl_trait_ref(impl_def_id) {
38 debug!("(checking implementation) adding impl for trait '{:?}', item '{}'",
40 tcx.item_path_str(impl_def_id));
42 // Skip impls where one of the self type is an error type.
43 // This occurs with e.g. resolve failures (#30589).
44 if trait_ref.references_error() {
48 enforce_trait_manually_implementable(tcx, impl_def_id, trait_ref.def_id);
49 enforce_empty_impls_for_marker_traits(tcx, impl_def_id, trait_ref.def_id);
53 fn enforce_trait_manually_implementable(tcx: TyCtxt, impl_def_id: DefId, trait_def_id: DefId) {
54 let did = Some(trait_def_id);
55 let li = tcx.lang_items();
56 let span = tcx.sess.source_map().def_span(tcx.span_of_impl(impl_def_id).unwrap());
58 // Disallow *all* explicit impls of `Sized` and `Unsize` for now.
59 if did == li.sized_trait() {
60 struct_span_err!(tcx.sess,
63 "explicit impls for the `Sized` trait are not permitted")
64 .span_label(span, "impl of 'Sized' not allowed")
69 if did == li.unsize_trait() {
70 struct_span_err!(tcx.sess,
73 "explicit impls for the `Unsize` trait are not permitted")
74 .span_label(span, "impl of `Unsize` not allowed")
79 if tcx.features().unboxed_closures {
80 // the feature gate allows all Fn traits
84 let trait_name = if did == li.fn_trait() {
86 } else if did == li.fn_mut_trait() {
88 } else if did == li.fn_once_trait() {
91 return; // everything OK
93 struct_span_err!(tcx.sess,
96 "manual implementations of `{}` are experimental",
98 .span_label(span, format!("manual implementations of `{}` are experimental", trait_name))
99 .help("add `#![feature(unboxed_closures)]` to the crate attributes to enable")
103 /// We allow impls of marker traits to overlap, so they can't override impls
104 /// as that could make it ambiguous which associated item to use.
105 fn enforce_empty_impls_for_marker_traits(tcx: TyCtxt, impl_def_id: DefId, trait_def_id: DefId) {
106 if !tcx.trait_def(trait_def_id).is_marker {
110 if tcx.associated_item_def_ids(trait_def_id).is_empty() {
114 let span = tcx.sess.source_map().def_span(tcx.span_of_impl(impl_def_id).unwrap());
115 struct_span_err!(tcx.sess,
118 "impls for marker traits cannot contain items")
122 pub fn provide(providers: &mut Providers) {
123 use self::builtin::coerce_unsized_info;
124 use self::inherent_impls::{crate_inherent_impls, inherent_impls};
125 use self::inherent_impls_overlap::crate_inherent_impls_overlap_check;
127 *providers = Providers {
129 crate_inherent_impls,
131 crate_inherent_impls_overlap_check,
137 fn coherent_trait<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) {
138 let impls = tcx.hir().trait_impls(def_id);
139 for &impl_id in impls {
140 check_impl(tcx, impl_id);
142 for &impl_id in impls {
143 check_impl_overlap(tcx, impl_id);
145 builtin::check_trait(tcx, def_id);
148 pub fn check_coherence<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
149 for &trait_def_id in tcx.hir().krate().trait_impls.keys() {
150 ty::query::queries::coherent_trait::ensure(tcx, trait_def_id);
153 unsafety::check(tcx);
156 // these queries are executed for side-effects (error reporting):
157 ty::query::queries::crate_inherent_impls::ensure(tcx, LOCAL_CRATE);
158 ty::query::queries::crate_inherent_impls_overlap_check::ensure(tcx, LOCAL_CRATE);
161 /// Overlap: No two impls for the same trait are implemented for the
162 /// same type. Likewise, no two inherent impls for a given type
163 /// constructor provide a method with the same name.
164 fn check_impl_overlap<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, node_id: ast::NodeId) {
165 let impl_def_id = tcx.hir().local_def_id(node_id);
166 let trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap();
167 let trait_def_id = trait_ref.def_id;
169 if trait_ref.references_error() {
170 debug!("coherence: skipping impl {:?} with error {:?}",
171 impl_def_id, trait_ref);
175 // Trigger building the specialization graph for the trait of this impl.
176 // This will detect any overlap errors.
177 tcx.specialization_graph_of(trait_def_id);
179 // check for overlap with the automatic `impl Trait for Trait`
180 if let ty::Dynamic(ref data, ..) = trait_ref.self_ty().sty {
181 // This is something like impl Trait1 for Trait2. Illegal
182 // if Trait1 is a supertrait of Trait2 or Trait2 is not object safe.
184 if !tcx.is_object_safe(data.principal().def_id()) {
185 // This is an error, but it will be reported by wfcheck. Ignore it here.
186 // This is tested by `coherence-impl-trait-for-trait-object-safe.rs`.
188 let mut supertrait_def_ids =
189 traits::supertrait_def_ids(tcx, data.principal().def_id());
190 if supertrait_def_ids.any(|d| d == trait_def_id) {
191 let sp = tcx.sess.source_map().def_span(tcx.span_of_impl(impl_def_id).unwrap());
192 struct_span_err!(tcx.sess,
195 "the object type `{}` automatically implements the trait `{}`",
197 tcx.item_path_str(trait_def_id))
198 .span_label(sp, format!("`{}` automatically implements trait `{}`",
200 tcx.item_path_str(trait_def_id)))