Add overriding tests

test/dotc/tests.scala

@@ -51,6 +51,7 @@ class tests extends CompilerTest {
   @Test def pos_assignments() = compileFile(posDir, "assignments", doErase)
   @Test def pos_packageobject() = compileFile(posDir, "packageobject", doErase)
   @Test def pos_overloaded() = compileFile(posDir, "overloaded", doErase)
+  @Test def pos_overrides() = compileFile(posDir, "overrides", doErase)
   @Test def pos_templateParents() = compileFile(posDir, "templateParents", doErase)
   @Test def pos_structural() = compileFile(posDir, "structural", doErase)
   @Test def pos_overloadedAccess = compileFile(posDir, "overloadedAccess", doErase)
@@ -75,7 +76,7 @@ class tests extends CompilerTest {
   @Test def neg_autoTupling2 = compileFile(negDir, "autoTuplingTest", xerrors = 4)
   @Test def neg_companions = compileFile(negDir, "companions", xerrors = 1)
   @Test def neg_over = compileFile(negDir, "over", xerrors = 1)
-  @Test def neg_overrides = compileFile(negDir, "overrides", xerrors = 5)
+  @Test def neg_overrides = compileFile(negDir, "overrides", xerrors = 7)
   @Test def neg_projections = compileFile(negDir, "projections", xerrors = 1)
   @Test def neg_i39 = compileFile(negDir, "i39", xerrors = 1)
   @Test def neg_i50_volatile = compileFile(negDir, "i50-volatile", xerrors = 4)

tests/neg/overrides.scala

@@ -68,3 +68,14 @@ class X1 {
 class Y1 extends X1 {
   override def f(): B1 = ???
 }
+
+class X2 {
+  type T = A1
+}
+class Y2 extends X2 {
+  type T = B1
+}
+
+class X3 {
+  override type T = A1
+}

tests/pos/overrides.scala

@@ -11,3 +11,12 @@ class B extends A[Int] {
   f(2)()
 
 }
+
+class A1
+class A2
+class X1 {
+  type T = A1
+}
+class Y1 extends X1 {
+  override type T = A2
+}