convert inherent-impl-related things to on-demand queries

There are now 3 queries:

- inherent_impls(def-id): for a given type, get a `Rc<Vec<DefId>>` with
  all its inherent impls. This internally uses `crate_inherent_impls`,
  doing some hacks to keep the current deps (which, btw, are not clearly
  correct).
- crate_inherent_impls(crate): gathers up a map from types
  to `Rc<Vec<DefId>>`, touching the entire krate, possibly generating
  errors.
- crate_inherent_impls_overlap_check(crate): performs overlap checks
  between the inherent impls for a given type, generating errors.

11 files changed, 227 insertions, 186 deletions

diff --git a/src/librustc/dep_graph/dep_node.rs b/src/librustc/dep_graph/dep_node.rs
index 399af258e92..c4cbbc17d51 100644
--- a/src/librustc/dep_graph/dep_node.rs
+++ b/src/librustc/dep_graph/dep_node.rs
@@ -74,7 +74,6 @@ pub enum DepNode<D: Clone + Debug> {
     CoherenceCheckImpl(D),
     CoherenceOverlapCheck(D),
     CoherenceOverlapCheckSpecial(D),
-    CoherenceOverlapInherentCheck(D),
     CoherenceOrphanCheck(D),
     Variance,
     WfCheck(D),
@@ -251,7 +250,6 @@ impl<D: Clone + Debug> DepNode<D> {
             CoherenceCheckImpl(ref d) => op(d).map(CoherenceCheckImpl),
             CoherenceOverlapCheck(ref d) => op(d).map(CoherenceOverlapCheck),
             CoherenceOverlapCheckSpecial(ref d) => op(d).map(CoherenceOverlapCheckSpecial),
-            CoherenceOverlapInherentCheck(ref d) => op(d).map(CoherenceOverlapInherentCheck),
             CoherenceOrphanCheck(ref d) => op(d).map(CoherenceOrphanCheck),
             WfCheck(ref d) => op(d).map(WfCheck),
             TypeckItemType(ref d) => op(d).map(TypeckItemType),
diff --git a/src/librustc/dep_graph/dep_tracking_map.rs b/src/librustc/dep_graph/dep_tracking_map.rs
index 0f3108df9a8..b6a2360211c 100644
--- a/src/librustc/dep_graph/dep_tracking_map.rs
+++ b/src/librustc/dep_graph/dep_tracking_map.rs
@@ -81,21 +81,6 @@ impl<M: DepTrackingMapConfig> DepTrackingMap<M> {
     pub fn keys(&self) -> Vec<M::Key> {
         self.map.keys().cloned().collect()
     }
-
-    /// Append `elem` to the vector stored for `k`, creating a new vector if needed.
-    /// This is considered a write to `k`.
-    ///
-    /// NOTE: Caution is required when using this method. You should
-    /// be sure that nobody is **reading from the vector** while you
-    /// are writing to it. Eventually, it'd be nice to remove this.
-    pub fn push<E: Clone>(&mut self, k: M::Key, elem: E)
-        where M: DepTrackingMapConfig<Value=Vec<E>>
-    {
-        self.write(&k);
-        self.map.entry(k)
-                .or_insert(Vec::new())
-                .push(elem);
-    }
 }
 
 impl<M: DepTrackingMapConfig> MemoizationMap for RefCell<DepTrackingMap<M>> {
diff --git a/src/librustc/middle/cstore.rs b/src/librustc/middle/cstore.rs
index 225d6fc9bb2..50ec6f26d4b 100644
--- a/src/librustc/middle/cstore.rs
+++ b/src/librustc/middle/cstore.rs
@@ -176,7 +176,6 @@ pub trait CrateStore {
     fn item_generics_cloned(&self, def: DefId) -> ty::Generics;
     fn item_attrs(&self, def_id: DefId) -> Vec<ast::Attribute>;
     fn fn_arg_names(&self, did: DefId) -> Vec<ast::Name>;
-    fn inherent_implementations_for_type(&self, def_id: DefId) -> Vec<DefId>;
 
     // trait info
     fn implementations_of_trait(&self, filter: Option<DefId>) -> Vec<DefId>;
@@ -310,7 +309,6 @@ impl CrateStore for DummyCrateStore {
         { bug!("item_generics_cloned") }
     fn item_attrs(&self, def_id: DefId) -> Vec<ast::Attribute> { bug!("item_attrs") }
     fn fn_arg_names(&self, did: DefId) -> Vec<ast::Name> { bug!("fn_arg_names") }
-    fn inherent_implementations_for_type(&self, def_id: DefId) -> Vec<DefId> { vec![] }
 
     // trait info
     fn implementations_of_trait(&self, filter: Option<DefId>) -> Vec<DefId> { vec![] }
diff --git a/src/librustc/ty/maps.rs b/src/librustc/ty/maps.rs
index d4214dc429c..87fe27d92fc 100644
--- a/src/librustc/ty/maps.rs
+++ b/src/librustc/ty/maps.rs
@@ -12,7 +12,7 @@ use dep_graph::{DepGraph, DepNode, DepTrackingMap, DepTrackingMapConfig};
 use hir::def_id::{CrateNum, DefId, LOCAL_CRATE};
 use middle::const_val::ConstVal;
 use mir;
-use ty::{self, Ty, TyCtxt};
+use ty::{self, CrateInherentImpls, Ty, TyCtxt};
 
 use rustc_data_structures::indexed_vec::IndexVec;
 use std::cell::{RefCell, RefMut};
@@ -176,9 +176,15 @@ impl<'tcx> QueryDescription for queries::coherent_trait<'tcx> {
     }
 }
 
-impl<'tcx> QueryDescription for queries::coherent_inherent_impls<'tcx> {
+impl<'tcx> QueryDescription for queries::crate_inherent_impls<'tcx> {
+    fn describe(_: TyCtxt, k: CrateNum) -> String {
+        format!("all inherent impls defined in crate `{:?}`", k)
+    }
+}
+
+impl<'tcx> QueryDescription for queries::crate_inherent_impls_overlap_check<'tcx> {
     fn describe(_: TyCtxt, _: CrateNum) -> String {
-        format!("coherence checking all inherent impls")
+        format!("check for overlap between inherent impls defined in this crate")
     }
 }
 
@@ -368,7 +374,7 @@ define_maps! { <'tcx>
     /// Maps a DefId of a type to a list of its inherent impls.
     /// Contains implementations of methods that are inherent to a type.
     /// Methods in these implementations don't need to be exported.
-    pub inherent_impls: InherentImpls(DefId) -> Vec<DefId>,
+    pub inherent_impls: InherentImpls(DefId) -> Rc<Vec<DefId>>,
 
     /// Maps from the def-id of a function/method or const/static
     /// to its MIR. Mutation is done at an item granularity to
@@ -400,7 +406,15 @@ define_maps! { <'tcx>
 
     pub coherent_trait: coherent_trait_dep_node((CrateNum, DefId)) -> (),
 
-    pub coherent_inherent_impls: coherent_inherent_impls_dep_node(CrateNum) -> (),
+    /// Gets a complete map from all types to their inherent impls.
+    /// Not meant to be used directly outside of coherence.
+    /// (Defined only for LOCAL_CRATE)
+    pub crate_inherent_impls: crate_inherent_impls_dep_node(CrateNum) -> CrateInherentImpls,
+
+    /// Checks all types in the krate for overlap in their inherent impls. Reports errors.
+    /// Not meant to be used directly outside of coherence.
+    /// (Defined only for LOCAL_CRATE)
+    pub crate_inherent_impls_overlap_check: crate_inherent_impls_dep_node(CrateNum) -> (),
 
     /// Results of evaluating monomorphic constants embedded in
     /// other items, such as enum variant explicit discriminants.
@@ -413,7 +427,7 @@ fn coherent_trait_dep_node((_, def_id): (CrateNum, DefId)) -> DepNode<DefId> {
     DepNode::CoherenceCheckTrait(def_id)
 }
 
-fn coherent_inherent_impls_dep_node(_: CrateNum) -> DepNode<DefId> {
+fn crate_inherent_impls_dep_node(_: CrateNum) -> DepNode<DefId> {
     DepNode::Coherence
 }
 
diff --git a/src/librustc/ty/mod.rs b/src/librustc/ty/mod.rs
index d1404269958..d19f2ba2fad 100644
--- a/src/librustc/ty/mod.rs
+++ b/src/librustc/ty/mod.rs
@@ -31,7 +31,7 @@ use ty::subst::{Subst, Substs};
 use ty::util::IntTypeExt;
 use ty::walk::TypeWalker;
 use util::common::MemoizationMap;
-use util::nodemap::{NodeSet, FxHashMap};
+use util::nodemap::{NodeSet, DefIdMap, FxHashMap};
 
 use serialize::{self, Encodable, Encoder};
 use std::borrow::Cow;
@@ -2345,34 +2345,6 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
         def.flags.get().intersects(TraitFlags::HAS_DEFAULT_IMPL)
     }
 
-    /// Populates the type context with all the inherent implementations for
-    /// the given type if necessary.
-    pub fn populate_inherent_implementations_for_type_if_necessary(self,
-                                                                   span: Span,
-                                                                   type_id: DefId) {
-        if type_id.is_local() {
-            // Make sure coherence of inherent impls ran already.
-            ty::queries::coherent_inherent_impls::force(self, span, LOCAL_CRATE);
-            return
-        }
-
-        // The type is not local, hence we are reading this out of
-        // metadata and don't need to track edges.
-        let _ignore = self.dep_graph.in_ignore();
-
-        if self.populated_external_types.borrow().contains(&type_id) {
-            return
-        }
-
-        debug!("populate_inherent_implementations_for_type_if_necessary: searching for {:?}",
-               type_id);
-
-        let inherent_impls = self.sess.cstore.inherent_implementations_for_type(type_id);
-
-        self.maps.inherent_impls.borrow_mut().insert(type_id, inherent_impls);
-        self.populated_external_types.borrow_mut().insert(type_id);
-    }
-
     /// Populates the type context with all the implementations for the given
     /// trait if necessary.
     pub fn populate_implementations_for_trait_if_necessary(self, trait_id: DefId) {
@@ -2637,3 +2609,16 @@ pub fn provide(providers: &mut ty::maps::Providers) {
         ..*providers
     };
 }
+
+
+/// A map for the local crate mapping each type to a vector of its
+/// inherent impls. This is not meant to be used outside of coherence;
+/// rather, you should request the vector for a specific type via
+/// `ty::queries::inherent_impls::get(def_id)` so as to minimize your
+/// dependencies (constructing this map requires touching the entire
+/// crate).
+#[derive(Clone, Debug)]
+pub struct CrateInherentImpls {
+    pub inherent_impls: DefIdMap<Rc<Vec<DefId>>>,
+}
+
diff --git a/src/librustc_metadata/cstore_impl.rs b/src/librustc_metadata/cstore_impl.rs
index 7cac201f14f..9b781d28f88 100644
--- a/src/librustc_metadata/cstore_impl.rs
+++ b/src/librustc_metadata/cstore_impl.rs
@@ -109,6 +109,7 @@ provide! { <'tcx> tcx, def_id, cdata
     typeck_tables => { cdata.item_body_tables(def_id.index, tcx) }
     closure_kind => { cdata.closure_kind(def_id.index) }
     closure_type => { cdata.closure_ty(def_id.index, tcx) }
+    inherent_impls => { Rc::new(cdata.get_inherent_implementations_for_type(def_id.index)) }
 }
 
 impl CrateStore for cstore::CStore {
@@ -162,12 +163,6 @@ impl CrateStore for cstore::CStore {
         self.get_crate_data(did.krate).get_fn_arg_names(did.index)
     }
 
-    fn inherent_implementations_for_type(&self, def_id: DefId) -> Vec<DefId>
-    {
-        self.dep_graph.read(DepNode::MetaData(def_id));
-        self.get_crate_data(def_id.krate).get_inherent_implementations_for_type(def_id.index)
-    }
-
     fn implementations_of_trait(&self, filter: Option<DefId>) -> Vec<DefId>
     {
         if let Some(def_id) = filter {
diff --git a/src/librustc_typeck/check/method/probe.rs b/src/librustc_typeck/check/method/probe.rs
index dfa7ababca0..5b041892156 100644
--- a/src/librustc_typeck/check/method/probe.rs
+++ b/src/librustc_typeck/check/method/probe.rs
@@ -479,14 +479,9 @@ impl<'a, 'gcx, 'tcx> ProbeContext<'a, 'gcx, 'tcx> {
     }
 
     fn assemble_inherent_impl_candidates_for_type(&mut self, def_id: DefId) {
-        // Read the inherent implementation candidates for this type from the
-        // metadata if necessary.
-        self.tcx.populate_inherent_implementations_for_type_if_necessary(self.span, def_id);
-
-        if let Some(impl_infos) = self.tcx.maps.inherent_impls.borrow().get(&def_id) {
-            for &impl_def_id in impl_infos.iter() {
-                self.assemble_inherent_impl_probe(impl_def_id);
-            }
+        let impl_def_ids = ty::queries::inherent_impls::get(self.tcx, self.span, def_id);
+        for &impl_def_id in impl_def_ids.iter() {
+            self.assemble_inherent_impl_probe(impl_def_id);
         }
     }
 
diff --git a/src/librustc_typeck/coherence/inherent.rs b/src/librustc_typeck/coherence/inherent_impls.rs
index 9abf233de1f..3a39df505eb 100644
--- a/src/librustc_typeck/coherence/inherent.rs
+++ b/src/librustc_typeck/coherence/inherent_impls.rs
@@ -8,26 +8,82 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+//! The code in this module gathers up all of the inherent impls in
+//! the current crate and organizes them in a map. It winds up
+//! touching the whole crate and thus must be recomputed completely
+//! for any change, but it is very cheap to compute. In practice, most
+//! code in the compiler never *directly* requests this map. Instead,
+//! it requests the inherent impls specific to some type (via
+//! `ty::queries::inherent_impls::get(def_id)`). That value, however,
+//! is computed by selecting an idea from this table.
+
 use rustc::dep_graph::DepNode;
-use rustc::hir::def_id::DefId;
+use rustc::hir::def_id::{CrateNum, DefId, LOCAL_CRATE};
 use rustc::hir;
 use rustc::hir::itemlikevisit::ItemLikeVisitor;
-use rustc::lint;
-use rustc::traits::{self, Reveal};
-use rustc::ty::{self, TyCtxt};
+use rustc::ty::{self, CrateInherentImpls, TyCtxt};
+use rustc::util::nodemap::DefIdMap;
 
+use std::rc::Rc;
 use syntax::ast;
-use syntax_pos::Span;
+use syntax_pos::{DUMMY_SP, Span};
+
+/// On-demand query: yields a map containing all types mapped to their inherent impls.
+pub fn crate_inherent_impls<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
+                                      crate_num: CrateNum)
+                                      -> CrateInherentImpls {
+    assert_eq!(crate_num, LOCAL_CRATE);
+
+    let krate = tcx.hir.krate();
+    let mut collect = InherentCollect {
+        tcx,
+        impls_map: CrateInherentImpls {
+            inherent_impls: DefIdMap()
+        }
+    };
+    krate.visit_all_item_likes(&mut collect);
+    collect.impls_map
+}
+
+/// On-demand query: yields a vector of the inherent impls for a specific type.
+pub fn inherent_impls<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
+                                ty_def_id: DefId)
+                                -> Rc<Vec<DefId>> {
+    assert!(ty_def_id.is_local());
+
+    // NB. Until we adopt the red-green dep-tracking algorithm (see
+    // [the plan] for details on that), we do some hackery here to get
+    // the dependencies correct.  Basically, we use a `with_ignore` to
+    // read the result we want. If we didn't have the `with_ignore`,
+    // we would wind up with a dependency on the entire crate, which
+    // we don't want. Then we go and add dependencies on all the impls
+    // in the result (which is what we wanted).
+    //
+    // The result is a graph with an edge from `Hir(I)` for every impl
+    // `I` defined on some type `T` to `CoherentInherentImpls(T)`,
+    // thus ensuring that if any of those impls change, the set of
+    // inherent impls is considered dirty.
+    //
+    // [the plan]: https://github.com/rust-lang/rust-roadmap/issues/4
+
+    let result = tcx.dep_graph.with_ignore(|| {
+        let crate_map = ty::queries::crate_inherent_impls::get(tcx, DUMMY_SP, ty_def_id.krate);
+        match crate_map.inherent_impls.get(&ty_def_id) {
+            Some(v) => v.clone(),
+            None => Rc::new(vec![]),
+        }
+    });
+
+    for &impl_def_id in &result[..] {
+        tcx.dep_graph.read(DepNode::Hir(impl_def_id));
+    }
 
-pub fn check<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
-    tcx.visit_all_item_likes_in_krate(DepNode::CoherenceCheckImpl,
-                                      &mut InherentCollect { tcx });
-    tcx.visit_all_item_likes_in_krate(DepNode::CoherenceOverlapCheckSpecial,
-                                      &mut InherentOverlapChecker { tcx });
+    result
 }
 
 struct InherentCollect<'a, 'tcx: 'a> {
-    tcx: TyCtxt<'a, 'tcx, 'tcx>
+    tcx: TyCtxt<'a, 'tcx, 'tcx>,
+    impls_map: CrateInherentImpls,
 }
 
 impl<'a, 'tcx, 'v> ItemLikeVisitor<'v> for InherentCollect<'a, 'tcx> {
@@ -216,25 +272,19 @@ impl<'a, 'tcx, 'v> ItemLikeVisitor<'v> for InherentCollect<'a, 'tcx> {
 }
 
 impl<'a, 'tcx> InherentCollect<'a, 'tcx> {
-    fn check_def_id(&self, item: &hir::Item, def_id: DefId) {
+    fn check_def_id(&mut self, item: &hir::Item, def_id: DefId) {
         if def_id.is_local() {
             // Add the implementation to the mapping from implementation to base
             // type def ID, if there is a base type for this implementation and
             // the implementation does not have any associated traits.
             let impl_def_id = self.tcx.hir.local_def_id(item.id);
+            let mut rc_vec = self.impls_map.inherent_impls
+                                           .entry(def_id)
+                                           .or_insert_with(|| Rc::new(vec![]));
 
-            // Subtle: it'd be better to collect these into a local map
-            // and then write the vector only once all items are known,
-            // but that leads to degenerate dep-graphs. The problem is
-            // that the write of that big vector winds up having reads
-            // from *all* impls in the krate, since we've lost the
-            // precision basically.  This would be ok in the firewall
-            // model so once we've made progess towards that we can modify
-            // the strategy here. In the meantime, using `push` is ok
-            // because we are doing this as a pre-pass before anyone
-            // actually reads from `inherent_impls` -- and we know this is
-            // true beacuse we hold the refcell lock.
-            self.tcx.maps.inherent_impls.borrow_mut().push(def_id, impl_def_id);
+            // At this point, there should not be any clones of the
+            // `Rc`, so we can still safely push into it in place:
+            Rc::get_mut(&mut rc_vec).unwrap().push(impl_def_id);
         } else {
             struct_span_err!(self.tcx.sess,
                              item.span,
@@ -273,85 +323,3 @@ impl<'a, 'tcx> InherentCollect<'a, 'tcx> {
     }
 }
 
-struct InherentOverlapChecker<'a, 'tcx: 'a> {
-    tcx: TyCtxt<'a, 'tcx, 'tcx>
-}
-
-impl<'a, 'tcx> InherentOverlapChecker<'a, 'tcx> {
-    fn check_for_common_items_in_impls(&self, impl1: DefId, impl2: DefId) {
-        #[derive(Copy, Clone, PartialEq)]
-        enum Namespace {
-            Type,
-            Value,
-        }
-
-        let name_and_namespace = |def_id| {
-            let item = self.tcx.associated_item(def_id);
-            (item.name, match item.kind {
-                ty::AssociatedKind::Type => Namespace::Type,
-                ty::AssociatedKind::Const |
-                ty::AssociatedKind::Method => Namespace::Value,
-            })
-        };
-
-        let impl_items1 = self.tcx.associated_item_def_ids(impl1);
-        let impl_items2 = self.tcx.associated_item_def_ids(impl2);
-
-        for &item1 in &impl_items1[..] {
-            let (name, namespace) = name_and_namespace(item1);
-
-            for &item2 in &impl_items2[..] {
-                if (name, namespace) == name_and_namespace(item2) {
-                    let msg = format!("duplicate definitions with name `{}`", name);
-                    let node_id = self.tcx.hir.as_local_node_id(item1).unwrap();
-                    self.tcx.sess.add_lint(lint::builtin::OVERLAPPING_INHERENT_IMPLS,
-                                           node_id,
-                                           self.tcx.span_of_impl(item1).unwrap(),
-                                           msg);
-                }
-            }
-        }
-    }
-
-    fn check_for_overlapping_inherent_impls(&self, ty_def_id: DefId) {
-        let _task = self.tcx.dep_graph.in_task(DepNode::CoherenceOverlapInherentCheck(ty_def_id));
-
-        let inherent_impls = self.tcx.maps.inherent_impls.borrow();
-        let impls = match inherent_impls.get(&ty_def_id) {
-            Some(impls) => impls,
-            None => return,
-        };
-
-        for (i, &impl1_def_id) in impls.iter().enumerate() {
-            for &impl2_def_id in &impls[(i + 1)..] {
-                self.tcx.infer_ctxt((), Reveal::UserFacing).enter(|infcx| {
-                    if traits::overlapping_impls(&infcx, impl1_def_id, impl2_def_id).is_some() {
-                        self.check_for_common_items_in_impls(impl1_def_id, impl2_def_id)
-                    }
-                });
-            }
-        }
-    }
-}
-
-impl<'a, 'tcx, 'v> ItemLikeVisitor<'v> for InherentOverlapChecker<'a, 'tcx> {
-    fn visit_item(&mut self, item: &'v hir::Item) {
-        match item.node {
-            hir::ItemEnum(..) |
-            hir::ItemStruct(..) |
-            hir::ItemTrait(..) |
-            hir::ItemUnion(..) => {
-                let type_def_id = self.tcx.hir.local_def_id(item.id);
-                self.check_for_overlapping_inherent_impls(type_def_id);
-            }
-            _ => {}
-        }
-    }
-
-    fn visit_trait_item(&mut self, _trait_item: &hir::TraitItem) {
-    }
-
-    fn visit_impl_item(&mut self, _impl_item: &hir::ImplItem) {
-    }
-}
-
diff --git a/src/librustc_typeck/coherence/inherent_impls_overlap.rs b/src/librustc_typeck/coherence/inherent_impls_overlap.rs
new file mode 100644
index 00000000000..4b36072243c
--- /dev/null
+++ b/src/librustc_typeck/coherence/inherent_impls_overlap.rs
@@ -0,0 +1,102 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use rustc::hir::def_id::{CrateNum, DefId, LOCAL_CRATE};
+use rustc::hir;
+use rustc::hir::itemlikevisit::ItemLikeVisitor;
+use rustc::lint;
+use rustc::traits::{self, Reveal};
+use rustc::ty::{self, TyCtxt};
+
+use syntax_pos::DUMMY_SP;
+
+pub fn crate_inherent_impls_overlap_check<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
+                                                    crate_num: CrateNum) {
+    assert_eq!(crate_num, LOCAL_CRATE);
+    let krate = tcx.hir.krate();
+    krate.visit_all_item_likes(&mut InherentOverlapChecker { tcx });
+}
+
+struct InherentOverlapChecker<'a, 'tcx: 'a> {
+    tcx: TyCtxt<'a, 'tcx, 'tcx>
+}
+
+impl<'a, 'tcx> InherentOverlapChecker<'a, 'tcx> {
+    fn check_for_common_items_in_impls(&self, impl1: DefId, impl2: DefId) {
+        #[derive(Copy, Clone, PartialEq)]
+        enum Namespace {
+            Type,
+            Value,
+        }
+
+        let name_and_namespace = |def_id| {
+            let item = self.tcx.associated_item(def_id);
+            (item.name, match item.kind {
+                ty::AssociatedKind::Type => Namespace::Type,
+                ty::AssociatedKind::Const |
+                ty::AssociatedKind::Method => Namespace::Value,
+            })
+        };
+
+        let impl_items1 = self.tcx.associated_item_def_ids(impl1);
+        let impl_items2 = self.tcx.associated_item_def_ids(impl2);
+
+        for &item1 in &impl_items1[..] {
+            let (name, namespace) = name_and_namespace(item1);
+
+            for &item2 in &impl_items2[..] {
+                if (name, namespace) == name_and_namespace(item2) {
+                    let msg = format!("duplicate definitions with name `{}`", name);
+                    let node_id = self.tcx.hir.as_local_node_id(item1).unwrap();
+                    self.tcx.sess.add_lint(lint::builtin::OVERLAPPING_INHERENT_IMPLS,
+                                           node_id,
+                                           self.tcx.span_of_impl(item1).unwrap(),
+                                           msg);
+                }
+            }
+        }
+    }
+
+    fn check_for_overlapping_inherent_impls(&self, ty_def_id: DefId) {
+        let impls = ty::queries::inherent_impls::get(self.tcx, DUMMY_SP, ty_def_id);
+
+        for (i, &impl1_def_id) in impls.iter().enumerate() {
+            for &impl2_def_id in &impls[(i + 1)..] {
+                self.tcx.infer_ctxt((), Reveal::UserFacing).enter(|infcx| {
+                    if traits::overlapping_impls(&infcx, impl1_def_id, impl2_def_id).is_some() {
+                        self.check_for_common_items_in_impls(impl1_def_id, impl2_def_id)
+                    }
+                });
+            }
+        }
+    }
+}
+
+impl<'a, 'tcx, 'v> ItemLikeVisitor<'v> for InherentOverlapChecker<'a, 'tcx> {
+    fn visit_item(&mut self, item: &'v hir::Item) {
+        match item.node {
+            hir::ItemEnum(..) |
+            hir::ItemStruct(..) |
+            hir::ItemTrait(..) |
+            hir::ItemUnion(..) => {
+                let type_def_id = self.tcx.hir.local_def_id(item.id);
+                self.check_for_overlapping_inherent_impls(type_def_id);
+            }
+            _ => {}
+        }
+    }
+
+    fn visit_trait_item(&mut self, _trait_item: &hir::TraitItem) {
+    }
+
+    fn visit_impl_item(&mut self, _impl_item: &hir::ImplItem) {
+    }
+}
+
diff --git a/src/librustc_typeck/coherence/mod.rs b/src/librustc_typeck/coherence/mod.rs
index 6abd061e81f..b3a7b612dd5 100644
--- a/src/librustc_typeck/coherence/mod.rs
+++ b/src/librustc_typeck/coherence/mod.rs
@@ -24,7 +24,8 @@ use syntax::ast;
 use syntax_pos::DUMMY_SP;
 
 mod builtin;
-mod inherent;
+mod inherent_impls;
+mod inherent_impls_overlap;
 mod orphan;
 mod overlap;
 mod unsafety;
@@ -103,10 +104,14 @@ fn enforce_trait_manually_implementable(tcx: TyCtxt, impl_def_id: DefId, trait_d
 
 pub fn provide(providers: &mut Providers) {
     use self::builtin::coerce_unsized_info;
+    use self::inherent_impls::{crate_inherent_impls, inherent_impls};
+    use self::inherent_impls_overlap::crate_inherent_impls_overlap_check;
 
     *providers = Providers {
         coherent_trait,
-        coherent_inherent_impls,
+        crate_inherent_impls,
+        inherent_impls,
+        crate_inherent_impls_overlap_check,
         coerce_unsized_info,
         ..*providers
     };
@@ -126,10 +131,6 @@ fn coherent_trait<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
     builtin::check_trait(tcx, def_id);
 }
 
-fn coherent_inherent_impls<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, _: CrateNum) {
-    inherent::check(tcx);
-}
-
 pub fn check_coherence<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
     let _task = tcx.dep_graph.in_task(DepNode::Coherence);
     for &trait_def_id in tcx.hir.krate().trait_impls.keys() {
@@ -140,5 +141,7 @@ pub fn check_coherence<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
     orphan::check(tcx);
     overlap::check_default_impls(tcx);
 
-    ty::queries::coherent_inherent_impls::get(tcx, DUMMY_SP, LOCAL_CRATE);
+    // these queries are executed for side-effects (error reporting):
+    ty::queries::crate_inherent_impls::get(tcx, DUMMY_SP, LOCAL_CRATE);
+    ty::queries::crate_inherent_impls_overlap_check::get(tcx, DUMMY_SP, LOCAL_CRATE);
 }
diff --git a/src/librustdoc/clean/inline.rs b/src/librustdoc/clean/inline.rs
index c4476483186..cc30fdf56fc 100644
--- a/src/librustdoc/clean/inline.rs
+++ b/src/librustdoc/clean/inline.rs
@@ -232,14 +232,12 @@ fn build_type_alias(cx: &DocContext, did: DefId) -> clean::Typedef {
 
 pub fn build_impls(cx: &DocContext, did: DefId) -> Vec<clean::Item> {
     let tcx = cx.tcx;
-    tcx.populate_inherent_implementations_for_type_if_necessary(DUMMY_SP, did);
     let mut impls = Vec::new();
 
-    if let Some(i) = tcx.maps.inherent_impls.borrow().get(&did) {
-        for &did in i.iter() {
-            build_impl(cx, did, &mut impls);
-        }
+    for &did in ty::queries::inherent_impls::get(tcx, DUMMY_SP, did).iter() {
+        build_impl(cx, did, &mut impls);
     }
+
     // If this is the first time we've inlined something from another crate, then
     // we inline *all* impls from all the crates into this crate. Note that there's
     // currently no way for us to filter this based on type, and we likely need