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>

scripts/qapi-types.py

@@ -269,7 +269,10 @@ def visit_array_type(self, name, info, element_type):
     def visit_object_type(self, name, info, base, members, variants):
         self._fwdecl += gen_fwd_object_or_array(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.decl += gen_union(name, base, variants)
         else:
             self.decl += gen_struct(name, base, members)

scripts/qapi-visit.py

@@ -364,7 +364,10 @@ def visit_array_type(self, name, info, element_type):
     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)

scripts/qapi.py

@@ -957,6 +957,9 @@ def visit(self, visitor):
 
 class QAPISchemaObjectType(QAPISchemaType):
     def __init__(self, name, info, base, local_members, variants):
+        # struct has local_members, optional base, and no variants
+        # flat union has base, variants, and no local_members
+        # simple union has local_members, variants, and no base
         QAPISchemaType.__init__(self, name, info)
         assert base is None or isinstance(base, str)
         for m in local_members:
@@ -1048,10 +1051,10 @@ def __init__(self, tag_name, tag_member, variants):
         self.variants = variants
 
     def check(self, schema, members, seen):
-        if self.tag_name:
+        if self.tag_name:    # flat union
             self.tag_member = seen[self.tag_name]
-        else:
-            self.tag_member.check(schema, members, seen)
+        if seen:
+            assert self.tag_member in seen.itervalues()
         assert isinstance(self.tag_member.type, QAPISchemaEnumType)
         for v in self.variants:
             vseen = dict(seen)
@@ -1085,6 +1088,7 @@ def __init__(self, name, info, variants):
         self.variants = variants
 
     def check(self, schema):
+        self.variants.tag_member.check(schema, [], {})
         self.variants.check(schema, [], {})
 
     def json_type(self):
@@ -1270,13 +1274,14 @@ def _def_union_type(self, expr, info):
         if tag_name:
             variants = [self._make_variant(key, value)
                         for (key, value) in data.iteritems()]
+            members = []
         else:
             variants = [self._make_simple_variant(key, value, info)
                         for (key, value) in data.iteritems()]
             tag_member = self._make_implicit_tag(name, info, variants)
+            members = [tag_member]
         self._def_entity(
-            QAPISchemaObjectType(name, info, base,
-                                 self._make_members(OrderedDict(), info),
+            QAPISchemaObjectType(name, info, base, members,
                                  QAPISchemaObjectTypeVariants(tag_name,
                                                               tag_member,
                                                               variants)))

tests/qapi-schema/qapi-schema-test.out

@@ -132,6 +132,7 @@ object UserDefFlatUnion2
     case value2: UserDefB
     case value3: UserDefA
 object UserDefNativeListUnion
+    member type: UserDefNativeListUnionKind optional=False
     case integer: :obj-intList-wrapper
     case s8: :obj-int8List-wrapper
     case s16: :obj-int16List-wrapper
@@ -187,6 +188,7 @@ object __org.qemu_x-Struct
 object __org.qemu_x-Struct2
     member array: __org.qemu_x-Union1List optional=False
 object __org.qemu_x-Union1
+    member type: __org.qemu_x-Union1Kind optional=False
     case __org.qemu_x-branch: :obj-str-wrapper
 enum __org.qemu_x-Union1Kind ['__org.qemu_x-branch']
 object __org.qemu_x-Union2

tests/qapi-schema/union-clash-data.out

@@ -2,5 +2,6 @@ object :empty
 object :obj-int-wrapper
     member data: int optional=False
 object TestUnion
+    member type: TestUnionKind optional=False
     case data: :obj-int-wrapper
 enum TestUnionKind ['data']

tests/qapi-schema/union-empty.out

@@ -1,3 +1,4 @@
 object :empty
 object Union
+    member type: UnionKind optional=False
 enum UnionKind []