Add coherence test

Author: tiif

tests/ui/internal/auxiliary/unstable_impl_coherence_aux.rs

@@ -0,0 +1,15 @@
+#![allow(internal_features)]
+#![feature(staged_api)]
+#![feature(impl_stability)]
+#![allow(dead_code)]
+#![stable(feature = "a", since = "1.1.1" )]
+
+#[stable(feature = "a", since = "1.1.1" )]
+pub trait Trait {}
+
+#[unstable_feature_bound(foo)]
+#[unstable(feature = "foo", issue = "none" )]
+impl <T> Trait for T {}
+
+fn main() {
+}

tests/ui/internal/unstable_impl_coherence.disabled.stderr

@@ -0,0 +1,13 @@
+error[E0119]: conflicting implementations of trait `Trait` for type `LocalTy`
+  --> $DIR/unstable_impl_coherence.rs:12:1
+   |
+LL | impl aux::Trait for LocalTy{}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: conflicting implementation in crate `unstable_impl_coherence_aux`:
+           - impl<T> Trait for T
+             where unstable feature: `foo`;
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0119`.

tests/ui/internal/unstable_impl_coherence.enabled.stderr

@@ -0,0 +1,13 @@
+error[E0119]: conflicting implementations of trait `Trait` for type `LocalTy`
+  --> $DIR/unstable_impl_coherence.rs:12:1
+   |
+LL | impl aux::Trait for LocalTy{}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: conflicting implementation in crate `unstable_impl_coherence_aux`:
+           - impl<T> Trait for T
+             where unstable feature: `foo`;
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0119`.

tests/ui/internal/unstable_impl_coherence.rs

@@ -0,0 +1,17 @@
+//@ aux-build:unstable_impl_coherence_aux.rs
+//@ revisions: enabled disabled
+
+#![cfg_attr(enabled, feature(foo))]
+extern crate unstable_impl_coherence_aux as aux;
+use aux::Trait;
+
+/// Coherence test for unstable impl.
+/// No matter feature `foo` is enabled or not, the impl
+/// for aux::Trait will be rejected by coherence checking.
+
+struct LocalTy;
+
+impl aux::Trait for LocalTy{}
+//~^ ERROR: conflicting implementations of trait `Trait` for type `LocalTy`
+
+fn main(){}