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)

8 files changed, 107 insertions, 7 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/pos/t5508-min-okay.scala b/test/files/pos/t5508-min-okay.scala
new file mode 100644
index 0000000000..3a38b9c5ea
--- /dev/null
+++ b/test/files/pos/t5508-min-okay.scala
@@ -0,0 +1,6 @@
+object Test {
+  trait NestedTrait { // must be nested and a trait
+    private val _st : Int = 0 // crashes if changed to private[this]
+    val escape = { () => _st }
+  }
+}
diff --git a/test/files/pos/t5508-min-okay2.scala b/test/files/pos/t5508-min-okay2.scala
new file mode 100644
index 0000000000..935f28609c
--- /dev/null
+++ b/test/files/pos/t5508-min-okay2.scala
@@ -0,0 +1,4 @@
+trait TopTrait { // must be nested and a trait
+  private[this] val _st : Int = 0 // crashes if TopTrait is not top level
+  val escape = { () => _st }
+}
diff --git a/test/files/pos/t5508-min.scala b/test/files/pos/t5508-min.scala
new file mode 100644
index 0000000000..f59d2bd6ad
--- /dev/null
+++ b/test/files/pos/t5508-min.scala
@@ -0,0 +1,6 @@
+object Test {
+  trait NestedTrait { // must be nested and a trait
+    private[this] val _st : Int = 0 // must be private[this]
+    val escape = { () => _st }
+  }
+}
diff --git a/test/files/pos/t5508.scala b/test/files/pos/t5508.scala
new file mode 100644
index 0000000000..2b49758045
--- /dev/null
+++ b/test/files/pos/t5508.scala
@@ -0,0 +1,83 @@
+package TestTestters
+
+trait Test1 {
+  private[this] var _st : Int = 0
+  def close : PartialFunction[Any,Any] = {
+    case x : Int =>
+      _st = identity(_st)
+  }
+}
+
+object Base1 {
+  trait Test2 {
+    private[this] var _st : Int = 0
+    def close : PartialFunction[Any,Any] = {
+      case x : Int =>
+  _st = identity(_st)
+    }
+  }
+}
+
+class Test3 {
+  private[this] var _st : Int = 0
+  def close : PartialFunction[Any,Any] = {
+    case x : Int =>
+      _st = 1
+  }
+}
+
+object Base2 {
+  class Test4 {
+    private[this] var _st : Int = 0
+    def close : PartialFunction[Any,Any] = {
+      case x : Int =>
+  _st = 1
+    }
+  }
+}
+
+class Base3 {
+  trait Test5 {
+    private[this] var _st : Int = 0
+    def close : PartialFunction[Any,Any] = {
+      case x : Int =>
+  _st = 1
+    }
+  }
+}
+
+object Base4 {
+  trait Test6 {
+    private[this] var _st : Int = 0
+    def close : PartialFunction[Any,Any] = {
+      case x : Int => ()
+    }
+  }
+}
+
+object Base5 {
+  trait Test7 {
+    private[this] var _st : Int = 0
+    def close = () => {
+      _st = 1
+    }
+  }
+}
+
+object Base6 {
+  class Test8 {
+    private[this] var _st : Int = 0
+    def close = () => {
+      _st = 1
+    }
+  }
+}
+
+object Base7 {
+  trait Test9 {
+    var st : Int = 0
+    def close = () => {
+      st = 1
+    }
+  }
+}
diff --git a/test/files/neg/t6231.scala b/test/files/pos/t6231.scala
index 1e5b4e0e1a..1e5b4e0e1a 100644
--- a/test/files/neg/t6231.scala
+++ b/test/files/pos/t6231.scala
diff --git a/test/files/pos/t6231b.scala b/test/files/pos/t6231b.scala
new file mode 100644
index 0000000000..b4ddfe785b
--- /dev/null
+++ b/test/files/pos/t6231b.scala
@@ -0,0 +1,8 @@
+class Test {
+  def f1(t: String) = {
+    trait T {
+      def xs = Nil map (_ => t)
+    }
+    ()
+  }
+}