allow escaping bound vars when normalizing ty::Opaque

src/test/ui/mir/issue-75419-validation-impl-trait.rs

@@ -0,0 +1,13 @@
+// build-pass
+
+// This used to fail MIR validation due to the types on both sides of
+// an assignment not being equal.
+// The failure doesn't occur with a check-only build.
+
+fn iter_slice<'a, T>(xs: &'a [T]) -> impl Iterator<Item = &'a T> {
+    xs.iter()
+}
+
+fn main() {
+    iter_slice::<()> as fn(_) -> _;
+}