[Qemu-devel] [PATCH for-2.5 1/4] qapi: Add type.is_empty() helper

[Eric Blake <eblake@redhat.com>]

And use it in qapi-types and qapi-event.  Down the road, we may
want to lift our artificial restriction of no variants at the
top level of an event, at which point, inlining our check for
whether members is empty will no longer be sufficient.  More
immediately, the new .is_empty() helper will help fix a bug in
qapi-visit.

Signed-off-by: Eric Blake <eblake@redhat.com>
---
 scripts/qapi-event.py | 6 +++---
 scripts/qapi-types.py | 2 +-
 scripts/qapi.py       | 3 +++
 3 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/scripts/qapi-event.py b/scripts/qapi-event.py
index 720486f..51128f4 100644
--- a/scripts/qapi-event.py
+++ b/scripts/qapi-event.py
@@ -39,7 +39,7 @@ 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('''
     QmpOutputVisitor *qov;
     Visitor *v;
@@ -58,7 +58,7 @@ 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('''
     qov = qmp_output_visitor_new();
     g_assert(qov);
@@ -90,7 +90,7 @@ 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:
     qmp_output_visitor_cleanup(qov);
diff --git a/scripts/qapi-types.py b/scripts/qapi-types.py
index b37900f..2d843a5 100644
--- a/scripts/qapi-types.py
+++ b/scripts/qapi-types.py
@@ -83,7 +83,7 @@ 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:
+    if (not base or base.is_empty()) and not members:
         ret += mcgen('''
     char qapi_dummy_field_for_empty_struct;
 ''')
diff --git a/scripts/qapi.py b/scripts/qapi.py
index 7c50cc4..744dc23 100644
--- a/scripts/qapi.py
+++ b/scripts/qapi.py
@@ -996,6 +996,9 @@ class QAPISchemaObjectType(QAPISchemaType):
         # See QAPISchema._make_implicit_object_type()
         return self.name[0] == ':'

+    def is_empty(self):
+        return not self.members and not self.variants
+
     def c_name(self):
         assert not self.is_implicit()
         return QAPISchemaType.c_name(self)
-- 
2.4.3