1 files changed, 49 insertions, 0 deletions
diff --git a/src/test/ui/associated-types/associated-types-coherence-failure.rs b/src/test/ui/associated-types/associated-types-coherence-failure.rs
new file mode 100644
index 000000000..c33f2ac96
--- /dev/null
+++ b/src/test/ui/associated-types/associated-types-coherence-failure.rs
@@ -0,0 +1,49 @@
+// Test that coherence detects overlap when some of the types in the
+// impls are projections of associated type. Issue #20624.
+
+use std::marker::PhantomData;
+use std::ops::Deref;
+
+pub struct Cow<'a, B: ?Sized>(PhantomData<(&'a (),B)>);
+
+/// Trait for moving into a `Cow`
+pub trait IntoCow<'a, B: ?Sized> {
+    /// Moves `self` into `Cow`
+    fn into_cow(self) -> Cow<'a, B>;
+}
+
+impl<'a, B: ?Sized> IntoCow<'a, B> for <B as ToOwned>::Owned where B: ToOwned {
+    fn into_cow(self) -> Cow<'a, B> {
+        Cow(PhantomData)
+    }
+}
+
+impl<'a, B: ?Sized> IntoCow<'a, B> for Cow<'a, B> where B: ToOwned {
+//~^ ERROR E0119
+    fn into_cow(self) -> Cow<'a, B> {
+        self
+    }
+}
+
+impl<'a, B: ?Sized> IntoCow<'a, B> for &'a B where B: ToOwned {
+//~^ ERROR E0119
+    fn into_cow(self) -> Cow<'a, B> {
+        Cow(PhantomData)
+    }
+}
+
+impl ToOwned for u8 {
+    type Owned = &'static u8;
+    fn to_owned(&self) -> &'static u8 { panic!() }
+}
+
+/// A generalization of Clone to borrowed data.
+pub trait ToOwned {
+    type Owned;
+
+    /// Creates owned data from borrowed data, usually by copying.
+    fn to_owned(&self) -> Self::Owned;
+}
+
+
+fn main() {}