src/librustc_typeck/coherence/mod.rs

   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.
   4 //
   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.
  10
  11 // Coherence phase
  12 //
  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.
  17
  18 use hir::def_id::{CrateNum, DefId, LOCAL_CRATE};
  19 use rustc::ty::{self, TyCtxt, TypeFoldable};
  20 use rustc::ty::maps::Providers;
  21 use rustc::dep_graph::DepNode;
  22
  23 use syntax::ast;
  24 use syntax_pos::DUMMY_SP;
  25
  26 mod builtin;
  27 mod inherent_impls;
  28 mod inherent_impls_overlap;
  29 mod orphan;
  30 mod overlap;
  31 mod unsafety;
  32
  33 fn check_impl<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, node_id: ast::NodeId) {
  34     let impl_def_id = tcx.hir.local_def_id(node_id);
  35
  36     // If there are no traits, then this implementation must have a
  37     // base type.
  38
  39     if let Some(trait_ref) = tcx.impl_trait_ref(impl_def_id) {
  40         debug!("(checking implementation) adding impl for trait '{:?}', item '{}'",
  41                 trait_ref,
  42                 tcx.item_path_str(impl_def_id));
  43
  44         // Skip impls where one of the self type is an error type.
  45         // This occurs with e.g. resolve failures (#30589).
  46         if trait_ref.references_error() {
  47             return;
  48         }
  49
  50         enforce_trait_manually_implementable(tcx, impl_def_id, trait_ref.def_id);
  51         let trait_def = tcx.lookup_trait_def(trait_ref.def_id);
  52         trait_def.record_local_impl(tcx, impl_def_id, trait_ref);
  53     }
  54 }
  55
  56 fn enforce_trait_manually_implementable(tcx: TyCtxt, impl_def_id: DefId, trait_def_id: DefId) {
  57     let did = Some(trait_def_id);
  58     let li = &tcx.lang_items;
  59
  60     // Disallow *all* explicit impls of `Sized` and `Unsize` for now.
  61     if did == li.sized_trait() {
  62         let span = tcx.span_of_impl(impl_def_id).unwrap();
  63         struct_span_err!(tcx.sess,
  64                          span,
  65                          E0322,
  66                          "explicit impls for the `Sized` trait are not permitted")
  67             .span_label(span, &format!("impl of 'Sized' not allowed"))
  68             .emit();
  69         return;
  70     }
  71
  72     if did == li.unsize_trait() {
  73         let span = tcx.span_of_impl(impl_def_id).unwrap();
  74         span_err!(tcx.sess,
  75                   span,
  76                   E0328,
  77                   "explicit impls for the `Unsize` trait are not permitted");
  78         return;
  79     }
  80
  81     if tcx.sess.features.borrow().unboxed_closures {
  82         // the feature gate allows all Fn traits
  83         return;
  84     }
  85
  86     let trait_name = if did == li.fn_trait() {
  87         "Fn"
  88     } else if did == li.fn_mut_trait() {
  89         "FnMut"
  90     } else if did == li.fn_once_trait() {
  91         "FnOnce"
  92     } else {
  93         return; // everything OK
  94     };
  95     let mut err = struct_span_err!(tcx.sess,
  96                                    tcx.span_of_impl(impl_def_id).unwrap(),
  97                                    E0183,
  98                                    "manual implementations of `{}` are experimental",
  99                                    trait_name);
 100     help!(&mut err,
 101           "add `#![feature(unboxed_closures)]` to the crate attributes to enable");
 102     err.emit();
 103 }
 104
 105 pub fn provide(providers: &mut Providers) {
 106     use self::builtin::coerce_unsized_info;
 107     use self::inherent_impls::{crate_inherent_impls, inherent_impls};
 108     use self::inherent_impls_overlap::crate_inherent_impls_overlap_check;
 109
 110     *providers = Providers {
 111         coherent_trait,
 112         crate_inherent_impls,
 113         inherent_impls,
 114         crate_inherent_impls_overlap_check,
 115         coerce_unsized_info,
 116         ..*providers
 117     };
 118 }
 119
 120 fn coherent_trait<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 121                             (_, def_id): (CrateNum, DefId)) {
 122     tcx.populate_implementations_for_trait_if_necessary(def_id);
 123
 124     let impls = tcx.hir.trait_impls(def_id);
 125     for &impl_id in impls {
 126         check_impl(tcx, impl_id);
 127     }
 128     for &impl_id in impls {
 129         overlap::check_impl(tcx, impl_id);
 130     }
 131     builtin::check_trait(tcx, def_id);
 132 }
 133
 134 pub fn check_coherence<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
 135     let _task = tcx.dep_graph.in_task(DepNode::Coherence);
 136     for &trait_def_id in tcx.hir.krate().trait_impls.keys() {
 137         ty::queries::coherent_trait::get(tcx, DUMMY_SP, (LOCAL_CRATE, trait_def_id));
 138     }
 139
 140     unsafety::check(tcx);
 141     orphan::check(tcx);
 142     overlap::check_default_impls(tcx);
 143
 144     // these queries are executed for side-effects (error reporting):
 145     ty::queries::crate_inherent_impls::get(tcx, DUMMY_SP, LOCAL_CRATE);
 146     ty::queries::crate_inherent_impls_overlap_check::get(tcx, DUMMY_SP, LOCAL_CRATE);
 147 }