1 files changed, 25 insertions, 3 deletions
diff --git a/src/librustc_data_structures/stable_hasher.rs b/src/librustc_data_structures/stable_hasher.rs
index 0d0cf672489..f80cbfadf2e 100644
--- a/src/librustc_data_structures/stable_hasher.rs
+++ b/src/librustc_data_structures/stable_hasher.rs
@@ -192,6 +192,28 @@ impl<W> Hasher for StableHasher<W> {
 }
 
 
+/// Something that can provide a stable hashing context.
+pub trait StableHashingContextProvider {
+    type ContextType;
+    fn create_stable_hashing_context(&self) -> Self::ContextType;
+}
+
+impl<'a, T: StableHashingContextProvider> StableHashingContextProvider for &'a T {
+    type ContextType = T::ContextType;
+
+    fn create_stable_hashing_context(&self) -> Self::ContextType {
+        (**self).create_stable_hashing_context()
+    }
+}
+
+impl<'a, T: StableHashingContextProvider> StableHashingContextProvider for &'a mut T {
+    type ContextType = T::ContextType;
+
+    fn create_stable_hashing_context(&self) -> Self::ContextType {
+        (**self).create_stable_hashing_context()
+    }
+}
+
 /// Something that implements `HashStable<CTX>` can be hashed in a way that is
 /// stable across multiple compilation sessions.
 pub trait HashStable<CTX> {
@@ -292,7 +314,7 @@ impl<T: HashStable<CTX>, CTX> HashStable<CTX> for Vec<T> {
     }
 }
 
-impl<T: HashStable<CTX>, CTX> HashStable<CTX> for Box<T> {
+impl<T: ?Sized + HashStable<CTX>, CTX> HashStable<CTX> for Box<T> {
     #[inline]
     fn hash_stable<W: StableHasherResult>(&self,
                                           ctx: &mut CTX,
@@ -301,7 +323,7 @@ impl<T: HashStable<CTX>, CTX> HashStable<CTX> for Box<T> {
     }
 }
 
-impl<T: HashStable<CTX>, CTX> HashStable<CTX> for ::std::rc::Rc<T> {
+impl<T: ?Sized + HashStable<CTX>, CTX> HashStable<CTX> for ::std::rc::Rc<T> {
     #[inline]
     fn hash_stable<W: StableHasherResult>(&self,
                                           ctx: &mut CTX,
@@ -310,7 +332,7 @@ impl<T: HashStable<CTX>, CTX> HashStable<CTX> for ::std::rc::Rc<T> {
     }
 }
 
-impl<T: HashStable<CTX>, CTX> HashStable<CTX> for ::std::sync::Arc<T> {
+impl<T: ?Sized + HashStable<CTX>, CTX> HashStable<CTX> for ::std::sync::Arc<T> {
     #[inline]
     fn hash_stable<W: StableHasherResult>(&self,
                                           ctx: &mut CTX,