Put more implementation restrictions on value classes.

Nested objects, classes and lazy vals are disallowed at any
nesting level in value classes; e.g. lazy vals local to a
method defined in a value class. There are still allowed in
universal traits.

This is a temporary, implementation restriction that is planned
to be addressed in future releases of Scala. Error messages has
been updated to communicate that intent.

Moved tests for SI-5582 and SI-6408 to pending folder. They have
to stay there until implementation restrictions are addressed.

Closes SI-6408 and SI-6432.

Review by @odersky, @harrah and @adriaanm.

6 files changed, 57 insertions, 4 deletions

diff --git a/test/files/neg/t5882.check b/test/files/neg/t5882.check
index b9ca5a1b2a..e0958e19d9 100644
--- a/test/files/neg/t5882.check
+++ b/test/files/neg/t5882.check
@@ -1,7 +1,9 @@
-t5882.scala:4: error: nested object is not allowed in value class
+t5882.scala:4: error: implementation restriction: nested class is not allowed in value class
+This restriction is planned to be removed in subsequent releases.
   case class Scope()
              ^
-t5882.scala:5: error: nested object is not allowed in value class
+t5882.scala:5: error: implementation restriction: nested object is not allowed in value class
+This restriction is planned to be removed in subsequent releases.
   object Bar
          ^
 two errors found
diff --git a/test/files/neg/t6359.check b/test/files/neg/t6359.check
index 2aa1ac5035..5bcdc57331 100644
--- a/test/files/neg/t6359.check
+++ b/test/files/neg/t6359.check
@@ -1,7 +1,9 @@
-t6359.scala:3: error: value class may not have nested module definitions
+t6359.scala:3: error: implementation restriction: nested object is not allowed in value class
+This restriction is planned to be removed in subsequent releases.
       object X
              ^
-t6359.scala:4: error: value class may not have nested class definitions
+t6359.scala:4: error: implementation restriction: nested class is not allowed in value class
+This restriction is planned to be removed in subsequent releases.
       class Y
             ^
 two errors found
diff --git a/test/files/neg/valueclasses-impl-restrictions.check b/test/files/neg/valueclasses-impl-restrictions.check
new file mode 100644
index 0000000000..17d07ba960
--- /dev/null
+++ b/test/files/neg/valueclasses-impl-restrictions.check
@@ -0,0 +1,21 @@
+valueclasses-impl-restrictions.scala:3: error: implementation restriction: nested object is not allowed in value class
+This restriction is planned to be removed in subsequent releases.
+      object X
+             ^
+valueclasses-impl-restrictions.scala:4: error: implementation restriction: lazy val is not allowed in value class
+This restriction is planned to be removed in subsequent releases.
+      lazy val y = 1
+               ^
+valueclasses-impl-restrictions.scala:10: error: implementation restriction: nested trait is not allowed in value class
+This restriction is planned to be removed in subsequent releases.
+  trait I2 {
+        ^
+valueclasses-impl-restrictions.scala:16: error: implementation restriction: nested class is not allowed in value class
+This restriction is planned to be removed in subsequent releases.
+    val i2 = new I2 { val q = x.s }
+                 ^
+valueclasses-impl-restrictions.scala:22: error: implementation restriction: nested class is not allowed in value class
+This restriction is planned to be removed in subsequent releases.
+  private[this] class I2(val q: String)
+                      ^
+5 errors found
diff --git a/test/files/neg/valueclasses-impl-restrictions.scala b/test/files/neg/valueclasses-impl-restrictions.scala
new file mode 100644
index 0000000000..53396db958
--- /dev/null
+++ b/test/files/neg/valueclasses-impl-restrictions.scala
@@ -0,0 +1,28 @@
+class M(val t: Int) extends AnyVal {
+   def lazyString = {
+      object X
+      lazy val y = 1
+      () => X
+   }
+}
+
+class X1(val s: String) extends AnyVal {
+  trait I2 {
+   val q: String
+   def z = s + q
+  }
+
+  def y(x: X1) = {
+    val i2 = new I2 { val q = x.s }
+    i2.z
+  }
+}
+
+class X2(val s: String) extends AnyVal {
+  private[this] class I2(val q: String)
+
+  def y(i: Int) = {
+    val i2 = new I2(i.toString)
+    i2.q + s
+  }
+}
diff --git a/test/files/run/t5882.scala b/test/pending/run/t5882.scala
index 47996d3068..47996d3068 100644
--- a/test/files/run/t5882.scala
+++ b/test/pending/run/t5882.scala
diff --git a/test/files/run/t6408.scala b/test/pending/run/t6408.scala
index ff17480b35..ff17480b35 100644
--- a/test/files/run/t6408.scala
+++ b/test/pending/run/t6408.scala