qapi: Drop useless 'data' member of unions

We started moving away from the use of the 'void *data' member
in the C union corresponding to a QAPI union back in commit
544a3731; recent commits have gotten rid of other uses.  Now
that it is completely unused, we can remove the member itself
as well as the FIXME comment.  Update the testsuite to drop the
negative test union-clash-data.

Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Daniel P. Berrange <berrange@redhat.com>
Message-Id: <1457021813-10704-11-git-send-email-eblake@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

scripts/qapi-types.py

@@ -116,17 +116,8 @@ def gen_upcast(name, base):
 
 
 def gen_variants(variants):
-    # FIXME: What purpose does data serve, besides preventing a union that
-    # has a branch named 'data'? We use it in qapi-visit.py to decide
-    # whether to bypass the switch statement if visiting the discriminator
-    # failed; but since we 0-initialize structs, and cannot tell what
-    # branch of the union is in use if the discriminator is invalid, there
-    # should not be any data leaks even without a data pointer.  Or, if
-    # 'data' is merely added to guarantee we don't have an empty union,
-    # shouldn't we enforce that at .json parse time?
     ret = mcgen('''
     union { /* union tag is @%(c_name)s */
-        void *data;
 ''',
                 c_name=c_name(variants.tag_member.name))
 

tests/Makefile

@@ -358,7 +358,6 @@ qapi-schema += unicode-str.json
 qapi-schema += union-base-no-discriminator.json
 qapi-schema += union-branch-case.json
 qapi-schema += union-clash-branches.json
-qapi-schema += union-clash-data.json
 qapi-schema += union-empty.json
 qapi-schema += union-invalid-base.json
 qapi-schema += union-optional-branch.json

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

-0

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

-# Union branch 'data'
-# FIXME: this parses, but then fails to compile due to a duplicate 'data'
-# (one from the branch name, another as a filler to avoid an empty union).
-# we should either detect the collision at parse time, or change the
-# generated struct to allow this to compile.
-{ 'union': 'TestUnion',
-  'data': { 'data': 'int' } }

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

-object :empty
-object :obj-int-wrapper
-    member data: int optional=False
-enum QType ['none', 'qnull', 'qint', 'qstring', 'qdict', 'qlist', 'qfloat', 'qbool']
-    prefix QTYPE
-object TestUnion
-    member type: TestUnionKind optional=False
-    case data: :obj-int-wrapper
-enum TestUnionKind ['data']