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