improve tests as suggested by review comments

1 files changed, 48 insertions, 0 deletions

diff --git a/src/test/ui/traits/trait-object-with-self-in-projection-output-repeated-supertrait.rs b/src/test/ui/traits/trait-object-with-self-in-projection-output-repeated-supertrait.rs
new file mode 100644
index 00000000000..46c083f9305
--- /dev/null
+++ b/src/test/ui/traits/trait-object-with-self-in-projection-output-repeated-supertrait.rs
@@ -0,0 +1,48 @@
+// compile-pass
+
+// Regression test related to #56288. Check that a supertrait projection (of
+// `Output`) that references `Self` is ok if there is another occurence of
+// the same supertrait that specifies the projection explicitly, even if
+// the projection's associated type is not explicitly specified in the object type.
+//
+// Note that in order for this to compile, we need the `Self`-referencing projection
+// to normalize fairly directly to a concrete type, otherwise the trait resolver
+// will hate us.
+//
+// There is a test in `trait-object-with-self-in-projection-output-bad.rs` that
+// having a normalizing, but `Self`-containing projection does not *by itself*
+// allow you to avoid writing the projected type (`Output`, in this example)
+// explicitly.
+
+trait ConstI32 {
+    type Out;
+}
+
+impl<T: ?Sized> ConstI32 for T {
+    type Out = i32;
+}
+
+trait Base {
+    type Output;
+}
+
+trait NormalizingHelper: Base<Output=<Self as ConstI32>::Out> + Base<Output=i32> {
+    type Target;
+}
+
+impl Base for u32
+{
+    type Output = i32;
+}
+
+impl NormalizingHelper for u32
+{
+    type Target = i32;
+}
+
+fn main() {
+    // Make sure this works both with and without the associated type
+    // being specified.
+    let _x: Box<dyn NormalizingHelper<Target=i32>> = Box::new(2u32);
+    let _y: Box<dyn NormalizingHelper<Target=i32, Output=i32>> = Box::new(2u32);
+}