SI-7571 Allow nesting of anonymous classes in value classes

5d9cde105e added deep prohibition of nested classes within
a value class. This has the undesirable side effect of
prohibiting partial functions literals in method bodies
of a value class.

The intention of that prohibition was to avoid problems
in code using Type Tests, such as:

    class C(val inner: A) extends AnyVal {
      class D
    }
    def foo(a: Any, other: C) = a match { case _ : other.D }

Here, the pattern usually checks that `a.$outer == other`.
But that is incongruent with the way that `other` is erased
to `A`.

However, not all nested classes could lead us into this trap.
This commit slightly relaxes the restriction to allow anonymous
classes, which can't appear in a type test.

The test shows that the translation generates working code.

1 files changed, 3 insertions, 1 deletions

diff --git a/test/files/neg/valueclasses-impl-restrictions.scala b/test/files/neg/valueclasses-impl-restrictions.scala
index 137f3f854c..f0577a94aa 100644
--- a/test/files/neg/valueclasses-impl-restrictions.scala
+++ b/test/files/neg/valueclasses-impl-restrictions.scala
@@ -12,8 +12,10 @@ class X1(val s: String) extends AnyVal {
   }
 
   def y(x: X1) = {
-    val i2 = new I2 { val q = x.s }
+    val i2 = new I2 { val q = x.s } // allowed as of SI-7571
     i2.z
+
+    { case x => x } : PartialFunction[Int, Int] // allowed
   }
 }