Test for #15264

Author: odersky

tests/pos/i15264.scala

@@ -0,0 +1,53 @@
+object priority:
+    // lower number = higher priority
+    class Prio0 extends Prio1
+    object Prio0 { given Prio0() }
+
+    class Prio1 extends Prio2
+    object Prio1 { given Prio1() }
+
+    class Prio2
+    object Prio2 { given Prio2() }
+
+object repro:
+    // analogous to cats Eq, Hash, Order:
+    class A[V]
+    class B[V] extends A[V]
+    class C[V] extends A[V]
+
+    class Q[V]
+
+    object context:
+        // prios work here, which is cool
+        given[V](using priority.Prio0): C[V] = new C[V]
+        given[V](using priority.Prio1): B[V] = new B[V]
+        given[V](using priority.Prio2): A[V] = new A[V]
+
+    object exports:
+        // so will these exports
+        export context.given
+
+    // if you import these don't import from 'context' above
+    object qcontext:
+        // base defs, like what you would get from cats
+        given gb: B[Int] = new B[Int]
+        given gc: C[Int] = new C[Int]
+
+        // these seem like they should work but don't
+        given gcq[V](using p0: priority.Prio0)(using c: C[V]): C[Q[V]] = new C[Q[V]]
+        given gbq[V](using p1: priority.Prio1)(using b: B[V]): B[Q[V]] = new B[Q[V]]
+        given gaq[V](using p2: priority.Prio2)(using a: A[V]): A[Q[V]] = new A[Q[V]]
+
+object test1:
+    import repro.*
+    import repro.exports.given
+
+    // these will work
+    val a = summon[A[Int]]
+
+object test2:
+    import repro.*
+    import repro.qcontext.given
+
+    // this one will fail as ambiguous - prios aren't having an effect
+    val a = summon[A[Q[Int]]]