Fix of #329.

Overriding pairs needs to match ExprTypes with field types. Closes #329.

Author: odersky

src/dotty/tools/dotc/transform/OverridingPairs.scala

@@ -43,7 +43,7 @@ object OverridingPairs {
         val info1 = self.memberInfo(sym1)
         val info2 = self.memberInfo(sym2)
         // info1.signature == info2.signature &&  // TODO enable for speed
-        info1 matches info2
+        info1.widenExpr matches info2.widenExpr
       }
 
     /** The symbols that can take part in an overriding pair */

test/dotc/tests.scala

@@ -82,8 +82,8 @@ class tests extends CompilerTest {
   @Test def neg_autoTupling = compileFile(posDir, "autoTuplingTest", "-language:noAutoTupling" :: Nil, xerrors = 4)
   @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 = 8)
+  @Test def neg_over = compileFile(negDir, "over", xerrors = 2)
+  @Test def neg_overrides = compileFile(negDir, "overrides", xerrors = 9)
   @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

@@ -100,3 +100,10 @@ trait TOverrider { this: TCommon =>
 class C2 extends C1 with TOverrider  // ... fails to override, here.
 
 }
+
+package p4 {
+
+  abstract class C[T] { def head: T }
+  case class D[T](head: Int) extends C[T]
+
+}