Test that if we promise to not impl what would overlap it doesn't actually overlap

Author: spastorino

src/test/ui/coherence/auxiliary/error_lib.rs

@@ -0,0 +1,5 @@
+#![crate_type = "lib"]
+#![feature(negative_impls)]
+
+pub trait Error {}
+impl !Error for &str {}

src/test/ui/coherence/coherence-overlap-negative-trait.rs

@@ -0,0 +1,14 @@
+// check-pass
+// aux-build:error_lib.rs
+//
+// Check that if we promise to not impl what would overlap it doesn't actually overlap
+
+extern crate error_lib as lib;
+use lib::Error;
+
+trait From<T> {}
+
+impl From<&str> for Box<dyn Error> {}
+impl<E> From<E> for Box<dyn Error> where E: Error {}
+
+fn main() {}