1 files changed, 26 insertions, 0 deletions
diff --git a/tests/ui/self/dyn-dispatch-do-not-mix-normalized-and-unnormalized.rs b/tests/ui/self/dyn-dispatch-do-not-mix-normalized-and-unnormalized.rs
new file mode 100644
index 00000000000..2bc70de2a34
--- /dev/null
+++ b/tests/ui/self/dyn-dispatch-do-not-mix-normalized-and-unnormalized.rs
@@ -0,0 +1,26 @@
+//@ check-pass
+
+// Regression test for <https://github.com/rust-lang/rust/issues/138937>.
+
+// Previously, we'd take the normalized param env's clauses which included
+// `<PF as TraitC>::Value = i32`, which comes from the supertraits of `TraitD`
+// after normalizing `<PF as TraitC>::Value = <PF as TraitD>::Scalar`. Since
+// `normalize_param_env_or_error` ends up re-elaborating `PF: TraitD`, we'd
+// end up with both versions of this predicate (normalized and unnormalized).
+// Since these projections preds are not equal, we'd fail with ambiguity.
+
+trait TraitB<T> {}
+
+trait TraitC: TraitB<Self::Value> {
+    type Value;
+}
+
+trait TraitD: TraitC<Value = Self::Scalar> {
+    type Scalar;
+}
+
+trait TraitE {
+    fn apply<PF: TraitD<Scalar = i32>>(&self);
+}
+
+fn main() {}