qapi: Add type.is_empty() helper

In the near future, we want to lift our artificial restriction of
no variants at the top level of an event, at which point the
currently open-coded check for empty members will become
insufficient.  Factor it out into a new helper method is_empty()
now, and future-proof it by checking variants, too, along with an
assert that it is not used prior to the completion of .check().
Update places that were checking for (non-)empty .members to use
the new helper.

All of the current callers assert that there are no variants (either
directly, or by qapi.py asserting that base types have no variants),
so this is not a semantic change.

No change to generated code.

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1468468228-27827-6-git-send-email-eblake@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

4 files changed, 11 insertions, 7 deletions

diff --git a/scripts/qapi-commands.py b/scripts/qapi-commands.py
index 34b6a3a07f..c93470cf2a 100644
--- a/scripts/qapi-commands.py
+++ b/scripts/qapi-commands.py
@@ -107,7 +107,7 @@ def gen_marshal(name, arg_type, ret_type):
 ''',
                      c_type=ret_type.c_type())
 
-    if arg_type and arg_type.members:
+    if arg_type and not arg_type.is_empty():
         ret += mcgen('''
     Visitor *v;
     %(c_name)s arg = {0};
@@ -137,7 +137,7 @@ def gen_marshal(name, arg_type, ret_type):
     ret += gen_call(name, arg_type, ret_type)
 
     # 'goto out' produced above for arg_type, and by gen_call() for ret_type
-    if (arg_type and arg_type.members) or ret_type:
+    if (arg_type and not arg_type.is_empty()) or ret_type:
         ret += mcgen('''
 
 out:
@@ -145,7 +145,7 @@ out:
     ret += mcgen('''
     error_propagate(errp, err);
 ''')
-    if arg_type and arg_type.members:
+    if arg_type and not arg_type.is_empty():
         ret += mcgen('''
     visit_free(v);
     v = qapi_dealloc_visitor_new();
diff --git a/scripts/qapi-event.py b/scripts/qapi-event.py
index 9c88627c9f..09c0a2a5d6 100644
--- a/scripts/qapi-event.py
+++ b/scripts/qapi-event.py
@@ -69,7 +69,7 @@ def gen_event_send(name, arg_type):
 ''',
                 proto=gen_event_send_proto(name, arg_type))
 
-    if arg_type and arg_type.members:
+    if arg_type and not arg_type.is_empty():
         ret += mcgen('''
     QObject *obj;
     Visitor *v;
@@ -88,7 +88,7 @@ def gen_event_send(name, arg_type):
 ''',
                  name=name)
 
-    if arg_type and arg_type.members:
+    if arg_type and not arg_type.is_empty():
         ret += mcgen('''
     v = qmp_output_visitor_new(&obj);
 
@@ -116,7 +116,7 @@ def gen_event_send(name, arg_type):
 ''',
                  c_enum=c_enum_const(event_enum_name, name))
 
-    if arg_type and arg_type.members:
+    if arg_type and not arg_type.is_empty():
         ret += mcgen('''
 out:
     visit_free(v);
diff --git a/scripts/qapi-types.py b/scripts/qapi-types.py
index 5ace2cf065..dabc42e047 100644
--- a/scripts/qapi-types.py
+++ b/scripts/qapi-types.py
@@ -91,7 +91,7 @@ struct %(c_name)s {
     # potential issues with attempting to malloc space for zero-length
     # structs in C, and also incompatibility with C++ (where an empty
     # struct is size 1).
-    if not (base and base.members) and not members and not variants:
+    if (not base or base.is_empty()) and not members and not variants:
         ret += mcgen('''
     char qapi_dummy_for_empty_struct;
 ''')
diff --git a/scripts/qapi.py b/scripts/qapi.py
index 400c4ef4a6..27284be144 100644
--- a/scripts/qapi.py
+++ b/scripts/qapi.py
@@ -999,6 +999,10 @@ class QAPISchemaObjectType(QAPISchemaType):
         # _def_predefineds()
         return self.name.startswith('q_')
 
+    def is_empty(self):
+        assert self.members is not None
+        return not self.members and not self.variants
+
     def c_name(self):
         assert self.name != 'q_empty'
         return QAPISchemaType.c_name(self)