Fix #2099: avoid loading a private member when recomputing a NamedType denot

ParamForwarding creates the following forwarder in B:
  private[this] def member: Int = super.member
Where the type for `super.member` is `TermRef(SubA, member)` and the
  symbol is the `val member` in `A`.
So far this is correct, but in later phases we might call `loadDenot` on
this `TermRef` which will end up calling `asMemberOf`, which before this
commit just did:
  prefix.member(name)
This is incorrect in our case because `SubA` also happens to have a
private `def member`, which means that our forwarder in B now forwards
to a private method in a superclass, this subsequently crashes in
`ExpandPrivate`.
(Note: in the bytecode, a private method cannot have the same name as an
overriden method, but this is already worked around in EnsurePrivate.)

The fix is simple: when we recompute a member, we should only look at
private members if the previous denotation was private.

3 files changed, 28 insertions, 0 deletions

diff --git a/tests/run/paramForwarding_separate.check b/tests/run/paramForwarding_separate.check
new file mode 100644
index 000000000..8df0c3100
--- /dev/null
+++ b/tests/run/paramForwarding_separate.check
@@ -0,0 +1,6 @@
+# Fields in A:
+private final int A.member$$local
+# Fields in SubA:
+
+# Fields in B:
+
diff --git a/tests/run/paramForwarding_separate/A_1.scala b/tests/run/paramForwarding_separate/A_1.scala
new file mode 100644
index 000000000..7e01f3ef1
--- /dev/null
+++ b/tests/run/paramForwarding_separate/A_1.scala
@@ -0,0 +1,3 @@
+class A(val member: Int)
+
+class SubA(member: Int) extends A(member)
diff --git a/tests/run/paramForwarding_separate/B_2.scala b/tests/run/paramForwarding_separate/B_2.scala
new file mode 100644
index 000000000..774967101
--- /dev/null
+++ b/tests/run/paramForwarding_separate/B_2.scala
@@ -0,0 +1,19 @@
+class B(member: Int) extends SubA(member)
+
+object Test {
+  def printFields(cls: Class[_]) =
+    println(cls.getDeclaredFields.map(_.toString).sorted.deep.mkString("\n"))
+
+  def main(args: Array[String]): Unit = {
+    val a = new A(10)
+    val subA = new SubA(11)
+    val b = new B(12)
+
+    println("# Fields in A:")
+    printFields(classOf[A])
+    println("# Fields in SubA:")
+    printFields(classOf[SubA])
+    println("# Fields in B:")
+    printFields(classOf[B])
+  }
+}