Add failing test that should pass

Author: spastorino

src/test/ui/coherence/coherence-negative-outlives-lifetimes.rs

@@ -0,0 +1,12 @@
+#![feature(negative_impls)]
+
+// FIXME: this should compile
+
+trait MyPredicate<'a> {}
+impl<'a, T> !MyPredicate<'a> for &T where T: 'a {}
+trait MyTrait<'a> {}
+impl<'a, T: MyPredicate<'a>> MyTrait<'a> for T {}
+impl<'a, T> MyTrait<'a> for &'a T {}
+//~^ ERROR: conflicting implementations of trait `MyTrait<'_>` for type `&_`
+
+fn main() {}

src/test/ui/coherence/coherence-negative-outlives-lifetimes.stderr

@@ -0,0 +1,11 @@
+error[E0119]: conflicting implementations of trait `MyTrait<'_>` for type `&_`
+  --> $DIR/coherence-negative-outlives-lifetimes.rs:9:1
+   |
+LL | impl<'a, T: MyPredicate<'a>> MyTrait<'a> for T {}
+   | ---------------------------------------------- first implementation here
+LL | impl<'a, T> MyTrait<'a> for &'a T {}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `&_`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0119`.