Merge pull request #6482 from dotty-staging/fix-#6474

Fix #6474: Add regression test

Author: OlivierBlanvillain

compiler/test-resources/repl/i6474

@@ -0,0 +1,22 @@
+scala> object Foo1 { type T[+A] = (A, Int) }
+// defined object Foo1
+scala> object Foo2 { type T[+A] = [+B] => (A, B) }
+// defined object Foo2
+scala> object Foo3 { type T[+A] = [+B] => [C] => (A, B) }
+// defined object Foo3
+scala> ((1, 2): Foo1.T[Int]): Foo1.T[Any]
+val res0: (Any, Int) = (1,2)
+scala> ((1, 2): Foo2.T[Int][Int]): Foo2.T[Any][Int]
+val res1: (Any, Int) = (1,2)
+scala> (1, 2): Foo3.T[Int][Int]
+1 | (1, 2): Foo3.T[Int][Int]
+  |         ^^^^^^^^^^^^^^^^
+  |         Missing type parameter for Foo3.T[Int][Int]
+scala> ((1, 2): Foo3.T[Int][Int][Int]): Foo3.T[Any][Int][Int]
+val res2: (Any, Int) = (1,2)
+scala> object Foo3 { type T[A] = [B] => [C] => (A, B) }
+// defined object Foo3
+scala> ((1, 2): Foo3.T[Int][Int][Int])
+val res3: (Int, Int) = (1,2)
+scala> ((1, 2): Foo3.T[Int][Int][Int])
+val res4: (Int, Int) = (1,2)