qapi: Track simple union tag in object.local_members

We were previously creating all unions with an empty list for
local_members.  However, it will make it easier to unify struct
and union generation if we include the generated tag member in
local_members.  That way, we can have a common code pattern:
visit the base (if any), visit the local members (if any), visit
the variants (if any).  The local_members of a flat union
remains empty (because the discriminator is already visited as
part of the base).  Then, by visiting tag_member.check() during
AlternateType.check(), we no longer need to call it during
Variants.check().

The various front end entities now exist as follows:
struct: optional base, optional local_members, no variants
simple union: no base, one-element local_members, variants with tag_member
  from local_members
flat union: base, no local_members, variants with tag_member from base
alternate: no base, no local_members, variants

With the new local members, we require a bit of finesse to
avoid assertions in the clients.

No change to generated code.

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1447836791-369-2-git-send-email-eblake@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

1 files changed, 4 insertions, 1 deletions

diff --git a/scripts/qapi-visit.py b/scripts/qapi-visit.py
index 3ef5c16a66..94cd11335e 100644
--- a/scripts/qapi-visit.py
+++ b/scripts/qapi-visit.py
@@ -364,7 +364,10 @@ class QAPISchemaGenVisitVisitor(QAPISchemaVisitor):
     def visit_object_type(self, name, info, base, members, variants):
         self.decl += gen_visit_decl(name)
         if variants:
-            assert not members      # not implemented
+            if members:
+                # Members other than variants.tag_member not implemented
+                assert len(members) == 1
+                assert members[0] == variants.tag_member
             self.defn += gen_visit_union(name, base, variants)
         else:
             self.defn += gen_visit_struct(name, base, members)