Merge branch 'master' into issue/5846,4597,4027,4112

Conflicts:
	src/library/scala/collection/MapLike.scala
	src/library/scala/collection/SortedMapLike.scala

1 files changed, 68 insertions, 0 deletions

diff --git a/test/files/neg/t4989.scala b/test/files/neg/t4989.scala
new file mode 100644
index 0000000000..e7ff80ed74
--- /dev/null
+++ b/test/files/neg/t4989.scala
@@ -0,0 +1,68 @@
+abstract class A0 {
+  def print(): String
+}
+
+class A extends A0 {
+  def print(): String = "A"
+}
+
+abstract class B extends A {
+  def print() : String
+}
+
+class C extends B {
+  override def print(): String = super.print() // should be an error
+}
+
+trait T extends B {
+  override def print(): String = super.print() // should be an error
+}
+
+class D extends A {
+  override def print(): String = super.print() // okay
+}
+
+
+// it's okay do this when trait are in the mix, as the
+// suitable super accessor methods are used.
+object ConcreteMethodAndIntermediaryAreTraits {
+  trait T1 {
+    def print(): String = ""
+  }
+
+  trait T2 extends T1 {
+    def print(): String
+  }
+
+  class C3 extends T2 {
+    def print(): String = super.print() // okay
+  }
+}
+
+object IntermediaryIsTrait {
+  class T1 {
+    def print(): String = ""
+  }
+
+  trait T2 extends T1 {
+    def print(): String
+  }
+
+  class C3 extends T2 {
+    override def print(): String = super.print() // okay
+  }
+}
+
+object ConcreteMethodIsTrait {
+  trait T1 {
+    def print(): String = ""
+  }
+
+  abstract class T2 extends T1 {
+    def print(): String
+  }
+
+  class C3 extends T2 {
+    override def print(): String = super.print() // okay
+  }
+}