Merge pull request #2044 from dotty-staging/abstract-type-in-object

Allow abstract type members in objects.

Author: odersky

compiler/src/dotty/tools/dotc/typer/Checking.scala

@@ -327,7 +327,7 @@ object Checking {
       if (!sym.is(Deferred))
         fail(i"`@native' members may not have implementation")
     }
-    else if (sym.is(Deferred, butNot = Param) && !sym.isSelfSym) {
+    else if (sym.is(Deferred, butNot = Param) && !sym.isType && !sym.isSelfSym) {
       if (!sym.owner.isClass || sym.owner.is(Module) || sym.owner.isAnonymousClass)
         fail(i"only classes can have declared but undefined members$varNote")
       checkWithDeferred(Private)

tests/neg/customArgs/typers.scala

@@ -30,7 +30,7 @@ object typers {
   }
 
   type L[X] = scala.collection.immutable.List[X]
-  type M[X, Y] <: scala.collection.immutable.Map[X, Y] // error: only classes can have declared but undefined members
+  type M[X, Y] <: scala.collection.immutable.Map[X, Y] // old-error: only classes can have declared but undefined members
 
   object hk {
     def f(x: L)  // error: missing type parameter

tests/neg/i1050c.scala

@@ -27,7 +27,8 @@ object Tiark4 {
     v.brand("boom!")
 }
 object V { // error: cannot be instantiated
-  type Y >: Any <: Nothing  // error: only classes can have declared but undefined members
+  type Y >: Any <: Nothing  // old-error: only classes can have declared but undefined members
+  type Z
 }
 object Tiark5 {
     trait A { type L <: Nothing }