assumptions_on_binders: Test mixed ambiguous ORs

tests/ui/assumptions_on_binders/mixed-ambiguous-alias-outlives.fail.stderr

@@ -0,0 +1,20 @@
+error: unable to satisfy constraints involving placeholders due to unknown implied bounds
+  --> $DIR/mixed-ambiguous-alias-outlives.rs:35:9
+   |
+LL |         forall<'a, U> {
+   |         ^^^^^^
+
+error: unable to satisfy constraints involving placeholders due to unknown implied bounds
+  --> $DIR/mixed-ambiguous-alias-outlives.rs:63:9
+   |
+LL |         forall<'a, U> {
+   |         ^^^^^^
+
+error: unable to satisfy constraints involving placeholders due to unknown implied bounds
+  --> $DIR/mixed-ambiguous-alias-outlives.rs:75:9
+   |
+LL |         forall<'a, U, V> {
+   |         ^^^^^^
+
+error: aborting due to 3 previous errors
+

tests/ui/assumptions_on_binders/mixed-ambiguous-alias-outlives.rs

@@ -0,0 +1,85 @@
+//@ revisions: pass fail
+//@[pass] check-pass
+//@ compile-flags: -Zassumptions-on-binders
+
+#![feature(test_binder_constraints, non_lifetime_binders)]
+#![expect(incomplete_features)]
+
+trait Project {
+    type Assoc;
+}
+
+impl<T> Project for T {
+    type Assoc = T;
+}
+
+// The alias involving U cannot leave its non-lifetime binder and becomes ambiguous.
+// Keep the other alias candidate until the root, where its outlives assumption is known.
+#[cfg(pass)]
+core::test_binder_constraints! {
+    impl<T: Project<Assoc: 'static>> {
+        forall<'a, U> {
+            or {
+                for<> <U as Project>::Assoc: 'a,
+                for<> T::Assoc: 'a,
+            }
+        }
+    }
+}
+
+// If the concrete candidate is rejected at the root, the ambiguous alternative must
+// still cause an error rather than disappearing with the rejected candidate.
+#[cfg(fail)]
+core::test_binder_constraints! {
+    impl<T: Project> {
+        forall<'a, U> {
+            //[fail]~^ ERROR unable to satisfy constraints involving placeholders
+            or {
+                for<> <U as Project>::Assoc: 'a,
+                for<> T::Assoc: 'a,
+            }
+        }
+    }
+}
+
+// The order of the alternatives must not change whether the bound can be proved.
+#[cfg(pass)]
+core::test_binder_constraints! {
+    impl<T: Project<Assoc: 'static>> {
+        forall<'a, U> {
+            or {
+                for<> T::Assoc: 'a,
+                for<> <U as Project>::Assoc: 'a,
+            }
+        }
+    }
+}
+
+// A required ambiguous constraint still makes the whole AND ambiguous, even when
+// its sibling is known to hold.
+#[cfg(fail)]
+core::test_binder_constraints! {
+    impl<T: Project<Assoc: 'static>> {
+        forall<'a, U> {
+            //[fail]~^ ERROR unable to satisfy constraints involving placeholders
+            for<> <U as Project>::Assoc: 'a,
+            for<> T::Assoc: 'a,
+        }
+    }
+}
+
+// Ambiguity shared by every OR alternative is still required after canonicalization.
+#[cfg(fail)]
+core::test_binder_constraints! {
+    impl {
+        forall<'a, U, V> {
+            //[fail]~^ ERROR unable to satisfy constraints involving placeholders
+            or {
+                for<> <U as Project>::Assoc: 'a,
+                for<> <V as Project>::Assoc: 'a,
+            }
+        }
+    }
+}
+
+fn main() {}