1 files changed, 62 insertions, 0 deletions
diff --git a/tests/ui/impl-unused-tps.rs b/tests/ui/impl-unused-tps.rs
new file mode 100644
index 00000000000..7cc1ae613bc
--- /dev/null
+++ b/tests/ui/impl-unused-tps.rs
@@ -0,0 +1,62 @@
+trait Foo<A> {
+    fn get(&self, A: &A) { }
+}
+
+trait Bar {
+    type Out;
+}
+
+impl<T> Foo<T> for [isize;0] {
+    // OK, T is used in `Foo<T>`.
+}
+
+impl<T,U> Foo<T> for [isize;1] {
+    //~^ ERROR the type parameter `U` is not constrained
+}
+
+impl<T,U> Foo<T> for [isize;2] where T : Bar<Out=U> {
+    // OK, `U` is now constrained by the output type parameter.
+}
+
+impl<T:Bar<Out=U>,U> Foo<T> for [isize;3] {
+    // OK, same as above but written differently.
+}
+
+impl<T,U> Foo<T> for U {
+    // OK, T, U are used everywhere. Note that the coherence check
+    // hasn't executed yet, so no errors about overlap.
+}
+
+impl<T,U> Bar for T {
+    //~^ ERROR the type parameter `U` is not constrained
+
+    type Out = U;
+
+    // Using `U` in an associated type within the impl is not good enough!
+}
+
+impl<T,U> Bar for T
+    where T : Bar<Out=U>
+{
+    //~^^^ ERROR the type parameter `U` is not constrained
+
+    // This crafty self-referential attempt is still no good.
+}
+
+impl<T,U,V> Foo<T> for T
+    where (T,U): Bar<Out=V>
+{
+    //~^^^ ERROR the type parameter `U` is not constrained
+    //~|   ERROR the type parameter `V` is not constrained
+
+    // Here, `V` is bound by an output type parameter, but the inputs
+    // are not themselves constrained.
+}
+
+impl<T,U,V> Foo<(T,U)> for T
+    where (T,U): Bar<Out=V>
+{
+    // As above, but both T and U ARE constrained.
+}
+
+fn main() { }