SI-5508 Fix crasher with private[this] in nested traits

Currently, accessors for private local trait fields are added
very late in the game when the `Mixin` tree transformer treats the
trait. By contrast, fields with weaker access have accessors created
eagerly in `Namers`.

    // Mixin#addLateInterfaceMembers
    val getter = member.getter(clazz)
    if (getter == NoSymbol) addMember(clazz, newGetter(member))

`addMember` mutates the type of the interface to add the getter.
(This seems like a pretty poor design: usually if a phase changes
types, it should do in an `InfoTransformer`.)

However, if an inner class or anonymous function of the trait
has been flattened to a spot where it precedes the trait in the
enclosing packages info, this code hasn't had a chance to run,
and the lookup of the getter crashes as mixins `postTransform`
runs over a selection of the not-yet-materialized getter.

    // Mixin#postTransform
	case Select(qual, name) if sym.owner.isImplClass && !isStaticOnly(sym) =>
	  val iface  = toInterface(sym.owner.tpe).typeSymbol
	  val ifaceGetter = sym getter iface

This commit ensures that `Flatten` lifts inner classes to
a position *after* the enclosing class in the stats of the
enclosing package.

Bonus fix: SI-7012 (the followup ticket to SI-6231 / SI-2897)

3 files changed, 0 insertions, 22 deletions

diff --git a/test/files/neg/t6231.check b/test/files/neg/t6231.check
deleted file mode 100644
index 6e107c97c7..0000000000
--- a/test/files/neg/t6231.check
+++ /dev/null
@@ -1,6 +0,0 @@
-t6231.scala:4: error: Implementation restriction: local trait Bug$X$1 is unable to automatically capture the
-free variable value ev$1 on behalf of <$anon: Function0>. You can manually assign it to a val inside the trait,
-and refer to that val in <$anon: Function0>. For more details, see SI-6231.
-      def qux = { () => ev }
-                        ^
-one error found
diff --git a/test/files/neg/t6231.flags b/test/files/neg/t6231.flags
deleted file mode 100644
index ac96850b69..0000000000
--- a/test/files/neg/t6231.flags
+++ /dev/null
@@ -1 +0,0 @@
--Ydelambdafy:inline
\ No newline at end of file
diff --git a/test/files/neg/t6231.scala b/test/files/neg/t6231.scala
deleted file mode 100644
index 1e5b4e0e1a..0000000000
--- a/test/files/neg/t6231.scala
+++ /dev/null
@@ -1,15 +0,0 @@
-object Bug {
-  def bar(ev: Any) = {
-    trait X {
-      def qux = { () => ev }
-    }
-    new X {}.qux()
-
-    // workaround
-    trait Y {
-      val ev2 = ev // manually capture `ev` so that `ev2` is added to the trait interface.
-      def qux = { () => ev2 }
-    }
-  }
-}
-