Consider well-formed predicates in min-specialization

src/test/ui/specialization/min_specialization/implcit-well-formed-bounds.rs

@@ -0,0 +1,30 @@
+// Test that specializing on the well-formed predicates of the trait and
+// self-type of an impl is allowed.
+
+// check-pass
+
+#![feature(min_specialization)]
+
+struct OrdOnly<T: Ord>(T);
+
+trait SpecTrait<U> {
+    fn f();
+}
+
+impl<T, U> SpecTrait<U> for T {
+    default fn f() {}
+}
+
+impl<T: Ord> SpecTrait<()> for OrdOnly<T> {
+    fn f() {}
+}
+
+impl<T: Ord> SpecTrait<OrdOnly<T>> for () {
+    fn f() {}
+}
+
+impl<T: Ord, U: Ord, V: Ord> SpecTrait<(OrdOnly<T>, OrdOnly<U>)> for &[OrdOnly<V>] {
+    fn f() {}
+}
+
+fn main() {}

src/test/ui/specialization/min_specialization/specialization_super_trait.rs

@@ -0,0 +1,18 @@
+// Test that supertraits can't be assumed in impls of
+// `rustc_specialization_trait`, as such impls would
+// allow specializing on the supertrait.
+
+#![feature(min_specialization)]
+#![feature(rustc_attrs)]
+
+#[rustc_specialization_trait]
+trait SpecMarker: Default {
+    fn f();
+}
+
+impl<T: Default> SpecMarker for T {
+    //~^ ERROR cannot specialize
+    fn f() {}
+}
+
+fn main() {}

src/test/ui/specialization/min_specialization/specialization_super_trait.stderr

@@ -0,0 +1,11 @@
+error: cannot specialize on trait `std::default::Default`
+  --> $DIR/specialization_super_trait.rs:13:1
+   |
+LL | / impl<T: Default> SpecMarker for T {
+LL | |
+LL | |     fn f() {}
+LL | | }
+   | |_^
+
+error: aborting due to previous error
+