SI-8708 Fix pickling of LOCAL_CHILD child of sealed classes

When a sealed class or trait has local children, they are not pickled
in as part of the children of the symbol (introduced in 12a2b3b to fix
Aladdin bug 1055). Instead the compiler adds a single child class
named LOCAL_CHILD. The parents of its ClassInfoType were wrong: the
first parent should be a class. For sealed traits, we were using the
trait itself.

Also, the LOCAL_CHILD dummy class was entered as a member of its
enclosing class, which is wrong: it represents a local (non-member)
class, and it's a synthetic dummy anyway.

1 files changed, 10 insertions, 1 deletions

diff --git a/src/compiler/scala/tools/nsc/symtab/classfile/Pickler.scala b/src/compiler/scala/tools/nsc/symtab/classfile/Pickler.scala
index 592c5497b5..34c5a899b7 100644
--- a/src/compiler/scala/tools/nsc/symtab/classfile/Pickler.scala
+++ b/src/compiler/scala/tools/nsc/symtab/classfile/Pickler.scala
@@ -186,7 +186,16 @@ abstract class Pickler extends SubComponent {
             val (locals, globals) = sym.children partition (_.isLocalClass)
             val children =
               if (locals.isEmpty) globals
-              else globals + sym.newClassWithInfo(tpnme.LOCAL_CHILD, List(sym.tpe), EmptyScope, pos = sym.pos)
+              else {
+                // The LOCAL_CHILD was introduced in 12a2b3b to fix Aladdin bug 1055. When a sealed
+                // class/trait has local subclasses, a single <local child> class symbol is added
+                // as pickled child (instead of a reference to the anonymous class; that was done
+                // initially, but seems not to work, as the bug shows).
+                // Adding the LOCAL_CHILD is necessary to retain exhaustivity warnings under separate
+                // compilation. See test neg/aladdin1055.
+                val parents = (if (sym.isTrait) List(definitions.ObjectTpe) else Nil) ::: List(sym.tpe)
+                globals + sym.newClassWithInfo(tpnme.LOCAL_CHILD, parents, EmptyScope, pos = sym.pos)
+              }
 
             putChildren(sym, children.toList sortBy (_.sealedSortName))
           }