SI-6793 Don't use super param accessors if inaccessible.

"Alias replacement" has been with us since 2005 (13c59adf9).

Given:

    package a {
      class C1(val v0: String)
      class C2(v1: String) extends a.C1(v1) { v1 }
    }

The reference to `v1` is rewritten as `C2.super.v0()`, and
no field is generated in `C2`.

(Oddly, this optimization doesn't seem to kick in if
these classes are in the empty package. That's probably
a distinct bug.)

However, this rewriting is done without consideration of
the accessibility of `v0` from `C2`.

This commit disables this optimization if there if `v0` is
not accessible.

4 files changed, 40 insertions, 2 deletions

diff --git a/src/compiler/scala/tools/nsc/typechecker/SuperAccessors.scala b/src/compiler/scala/tools/nsc/typechecker/SuperAccessors.scala
index 67639eb530..fa72ad64bf 100644
--- a/src/compiler/scala/tools/nsc/typechecker/SuperAccessors.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/SuperAccessors.scala
@@ -267,9 +267,16 @@ abstract class SuperAccessors extends transform.Transform with transform.TypingT
                 }
               }
 
-              // direct calls to aliases of param accessors to the superclass in order to avoid
+
+              def isAccessibleFromSuper(sym: Symbol) = {
+                val pre = SuperType(sym.owner.tpe, qual.tpe)
+                localTyper.context.isAccessible(sym, pre, superAccess = true)
+              }
+
+              // Direct calls to aliases of param accessors to the superclass in order to avoid
               // duplicating fields.
-              if (sym.isParamAccessor && sym.alias != NoSymbol) {
+              // ... but, only if accessible (SI-6793)
+              if (sym.isParamAccessor && sym.alias != NoSymbol && isAccessibleFromSuper(sym.alias)) {
                 val result = (localTyper.typedPos(tree.pos) {
                   Select(Super(qual, tpnme.EMPTY) setPos qual.pos, sym.alias)
                 }).asInstanceOf[Select]
diff --git a/test/files/run/t6793.scala b/test/files/run/t6793.scala
new file mode 100644
index 0000000000..0b1f1619af
--- /dev/null
+++ b/test/files/run/t6793.scala
@@ -0,0 +1,9 @@
+package a { class C1(private[a] val v0: String) }
+package b { class C2(v1: String) extends a.C1(v1) { def foo = v1 } }
+
+object Test extends App {
+  new b.C2("x")
+
+  val c2Fields = classOf[b.C2].getDeclaredFields
+  assert(c2Fields.size == 1, c2Fields.map(_.getName).toList)
+}
diff --git a/test/files/run/t6793b.scala b/test/files/run/t6793b.scala
new file mode 100644
index 0000000000..cb3f2fb2fa
--- /dev/null
+++ b/test/files/run/t6793b.scala
@@ -0,0 +1,11 @@
+package a {
+  class C1(val v0: String)
+  class C2(v1: String) extends a.C1(v1) { def foo = v1 }
+}
+
+object Test extends App {
+  new a.C2("x")
+
+  val c2Fields = classOf[a.C2].getDeclaredFields
+  assert(c2Fields.isEmpty, c2Fields.map(_.getName).mkString(", "))
+}
diff --git a/test/files/run/t6793c.scala b/test/files/run/t6793c.scala
new file mode 100644
index 0000000000..e28c7c81a1
--- /dev/null
+++ b/test/files/run/t6793c.scala
@@ -0,0 +1,11 @@
+package a {
+  class C1(private[a] val v0: String)
+  class C2(v1: String) extends a.C1(v1) { def foo = v1 }
+}
+
+object Test extends App {
+  new a.C2("x").foo
+
+  val c2Fields = classOf[a.C2].getDeclaredFields
+  assert(c2Fields.isEmpty, c2Fields.map(_.getName).toList)
+}