Add a Java protected member case, which can only call super

Author: dwijnand

compiler/src/dotty/tools/dotc/transform/ProtectedAccessors.scala

@@ -38,7 +38,7 @@ object ProtectedAccessors {
     sym.isTerm && sym.is(Protected) &&
     !sym.owner.is(Trait) && // trait methods need to be handled specially, are currently always public
     !insideBoundaryOf(sym) &&
-    !ctx.owner.enclosingClass.derivesFrom(sym.owner)
+    (sym.is(JavaDefined) || !ctx.owner.enclosingClass.derivesFrom(sym.owner))
 }
 
 class ProtectedAccessors extends MiniPhase {

tests/run/i17021.ext-java/A.java

@@ -0,0 +1,6 @@
+// Derives from run/i17021.defs, but with a Java protected member
+package p1;
+
+public class A {
+  protected int foo() { return 1; }
+}

tests/run/i17021.ext-java/Test.scala

@@ -0,0 +1,14 @@
+// Derives from run/i17021.defs
+// but with a Java protected member
+// which changes the behaviour
+package p2:
+  trait B extends p1.A:
+    def bar: Int = foo
+
+  class C extends B:
+    override def foo: Int = 2
+
+object Test:
+  def main(args: Array[String]): Unit =
+    val n = new p2.C().bar
+    assert(n == 1, n) // B can only call super.foo