SI-5954 Implementation restriction preventing companions in package objs

Companion objects (and thus also case classes) in package objects caused
an assert about an overloaded symbol when everything was compiled twice.
It's a hairy problem that doesn't fit in 2.10.1. So this fix adds an
implementation restriction. It also has a test to make sure the error
messages are clean and reasonably friendly, and does not catch other
things defined in package objects. The test includes a
commented out test in case somebody thinks they've solved the underlying
problem.

A handful of tests were falling afoul of the new implementation
restriction. I verified that they do in fact fail on second compile so
they aren't false casualties. But they do test real things we'd like
to work once the re-compile issue is fixed. So I added a -X flag to
disable the implementation restriction and made all the tests
accidentally clobbered by the restriction use that flag.

7 files changed, 67 insertions, 0 deletions

diff --git a/test/files/neg/t5954.check b/test/files/neg/t5954.check
new file mode 100644
index 0000000000..3ca47cd430
--- /dev/null
+++ b/test/files/neg/t5954.check
@@ -0,0 +1,16 @@
+t5954.scala:36: error: implementation restriction: package object A cannot contain case class D. Instead, class D should be placed directly in package A.
+  case class D()
+             ^
+t5954.scala:35: error: implementation restriction: package object A cannot contain companion object C. Instead, object C should be placed directly in package A.
+  object C
+         ^
+t5954.scala:34: error: implementation restriction: package object A cannot contain companion trait C. Instead, trait C should be placed directly in package A.
+  trait C
+        ^
+t5954.scala:33: error: implementation restriction: package object A cannot contain companion object B. Instead, object B should be placed directly in package A.
+  object B
+         ^
+t5954.scala:32: error: implementation restriction: package object A cannot contain companion class B. Instead, class B should be placed directly in package A.
+  class B
+        ^
+5 errors found
diff --git a/test/files/neg/t5954.scala b/test/files/neg/t5954.scala
new file mode 100644
index 0000000000..9e6f5392c7
--- /dev/null
+++ b/test/files/neg/t5954.scala
@@ -0,0 +1,46 @@
+// if you ever think you've fixed the underlying reason for the implementation restrictions
+// imposed by SI-5954, then here's a test that should pass with two "succes"es
+//
+//import scala.tools.partest._
+//
+//object Test extends DirectTest {
+//  def code = ???
+//
+//  def problemCode = """
+//    package object A {
+//      class B
+//      object B
+//      case class C()
+//    }
+//  """
+//
+//  def compileProblemCode() = {
+//    val classpath = List(sys.props("partest.lib"), testOutput.path) mkString sys.props("path.separator")
+//    compileString(newCompiler("-cp", classpath, "-d", testOutput.path))(problemCode)
+//  }
+//
+//  def show() : Unit = {
+//    for (i <- 0 until 2) {
+//      compileProblemCode()
+//      println(s"success ${i + 1}")
+//    }
+//  }
+//}
+
+package object A {
+  // these should be prevented by the implementation restriction
+  class B
+  object B
+  trait C
+  object C
+  case class D()
+  // all the rest of these should be ok
+  class E
+  object F
+  val g = "omg"
+  var h = "wtf"
+  def i = "lol"
+  type j = String
+  class K(val k : Int) extends AnyVal
+  implicit class L(val l : Int)
+}
diff --git a/test/files/pos/package-case.flags b/test/files/pos/package-case.flags
new file mode 100644
index 0000000000..2f174c4732
--- /dev/null
+++ b/test/files/pos/package-case.flags
@@ -0,0 +1 @@
+-Ycompanions-in-pkg-objs
diff --git a/test/files/pos/t2130-1.flags b/test/files/pos/t2130-1.flags
new file mode 100644
index 0000000000..2f174c4732
--- /dev/null
+++ b/test/files/pos/t2130-1.flags
@@ -0,0 +1 @@
+-Ycompanions-in-pkg-objs
diff --git a/test/files/pos/t2130-2.flags b/test/files/pos/t2130-2.flags
new file mode 100644
index 0000000000..2f174c4732
--- /dev/null
+++ b/test/files/pos/t2130-2.flags
@@ -0,0 +1 @@
+-Ycompanions-in-pkg-objs
diff --git a/test/files/pos/t3999b.flags b/test/files/pos/t3999b.flags
new file mode 100644
index 0000000000..2f174c4732
--- /dev/null
+++ b/test/files/pos/t3999b.flags
@@ -0,0 +1 @@
+-Ycompanions-in-pkg-objs
diff --git a/test/files/pos/t4052.flags b/test/files/pos/t4052.flags
new file mode 100644
index 0000000000..2f174c4732
--- /dev/null
+++ b/test/files/pos/t4052.flags
@@ -0,0 +1 @@
+-Ycompanions-in-pkg-objs