qapi: Fix command with named empty argument type

The generator special-cased

 { 'command':'foo', 'data': {} }

to avoid emitting a visitor variable, but failed to see that

 { 'struct':'NamedEmptyType, 'data': {} }
 { 'command':'foo', 'data':'NamedEmptyType' }

needs the same treatment.  There, the generator happily generates a
visitor to get no arguments, and a visitor to destroy no arguments;
and the compiler isn't happy with that, as demonstrated by the updated
qapi-schema-test.json:

  tests/test-qmp-marshal.c: In function ‘qmp_marshal_user_def_cmd0’:
  tests/test-qmp-marshal.c:264:14: error: variable ‘v’ set but not used [-Werror=unused-but-set-variable]
       Visitor *v;
                ^

No change to generated code except for the testsuite addition.

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1458254921-17042-3-git-send-email-eblake@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/scripts/qapi-commands.py b/scripts/qapi-commands.py
index edcbd10128..3784f33fcc 100644
--- a/scripts/qapi-commands.py
+++ b/scripts/qapi-commands.py
@@ -66,7 +66,7 @@ def gen_marshal_vars(arg_type, ret_type):
 ''',
                      c_type=ret_type.c_type())
 
-    if arg_type:
+    if arg_type and arg_type.members:
         ret += mcgen('''
     QmpInputVisitor *qiv = qmp_input_visitor_new_strict(QOBJECT(args));
     QapiDeallocVisitor *qdv;
@@ -98,7 +98,7 @@ def gen_marshal_vars(arg_type, ret_type):
 def gen_marshal_input_visit(arg_type, dealloc=False):
     ret = ''
 
-    if not arg_type:
+    if not arg_type or not arg_type.members:
         return ret
 
     if dealloc: