Merge pull request #5076 from dotty-staging/fix-5052

Forbid private override modifier combination

Author: allanrenucci

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

@@ -407,6 +407,7 @@ object Checking {
     checkCombination(Final, Sealed)
     checkCombination(Private, Protected)
     checkCombination(Abstract, Override)
+    checkCombination(Private, Override)
     checkCombination(Lazy, Transparent)
     checkCombination(Rewrite, Transparent)
     checkNoConflict(Lazy, ParamAccessor, s"parameter may not be `lazy`")

tests/neg/i5052.scala

@@ -0,0 +1,13 @@
+class Foo {
+  protected[this] def foo = 1
+  protected def foo2 = 1
+  val foo3 = 1
+
+}
+
+class Bar extends Foo {
+  // illegal combination of modifiers: `private` and `override`
+  override private[this] def foo = 2 // error
+  override private[this] def foo2 = 2 // error
+  override private val foo3 = 2 // error
+}