[Qemu-devel] [PATCH v8 26/35] 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>

---
v8: no change
v7: rebase to context change
v6: new patch
---
 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 1bef611..7103ec6 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('''
     QObject *obj;
     QmpOutputVisitor *qov;
@@ -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();
     v = qmp_output_get_visitor(qov);
@@ -88,7 +88,7 @@ out_obj:
 ''',
                  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 d3f631a..c70fae1 100644
--- a/scripts/qapi-types.py
+++ b/scripts/qapi-types.py
@@ -76,7 +76,7 @@ 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_field_for_empty_struct;
 ''')
diff --git a/scripts/qapi.py b/scripts/qapi.py
index 3b4c62e..a13c110 100644
--- a/scripts/qapi.py
+++ b/scripts/qapi.py
@@ -973,6 +973,9 @@ 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