Merge pull request #8420 from dotty-staging/fix-#3657

Fix #3657: Add test

Author: odersky

tests/neg/i3657.scala

@@ -0,0 +1,24 @@
+object App {
+  def main(args: Array[String]): Unit = {
+    trait ModuleSig {
+      type F[_, _]
+      type G[_]
+      type H[_]
+
+      trait FooSig {
+        type Type = F[G[Int], H[Int]]
+        def subst[F[_]](fa: F[Int]): F[Type]
+      }
+
+      val Foo: FooSig
+    }
+    val Module: ModuleSig = new ModuleSig {
+      type F[x[_]] = Int  // error
+
+      val Foo: FooSig = new FooSig {
+        // type Type = Int
+        def subst[F[_]](fa: F[Int]): F[Type] = fa
+      }
+    }
+  }
+}