qapi: Permit 'boxed' with empty type

We reject empty types with 'boxed': true.  We don't really need that
to work, but making it work is actually simpler than rejecting it, so
do that.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20190913201349.24332-9-armbru@redhat.com>

3 files changed, 9 insertions, 19 deletions

diff --git a/scripts/qapi/commands.py b/scripts/qapi/commands.py
index b929e07be4..7e3dd1068a 100644
--- a/scripts/qapi/commands.py
+++ b/scripts/qapi/commands.py
@@ -30,7 +30,7 @@ def gen_call(name, arg_type, boxed, ret_type):
 
     argstr = ''
     if boxed:
-        assert arg_type and not arg_type.is_empty()
+        assert arg_type
         argstr = '&arg, '
     elif arg_type:
         assert not arg_type.variants
@@ -96,7 +96,7 @@ def gen_marshal_decl(name):
 
 
 def gen_marshal(name, arg_type, boxed, ret_type):
-    have_args = arg_type and not arg_type.is_empty()
+    have_args = boxed or (arg_type and not arg_type.is_empty())
 
     ret = mcgen('''
 
diff --git a/scripts/qapi/common.py b/scripts/qapi/common.py
index 0fb1d1956a..c5c71287c3 100644
--- a/scripts/qapi/common.py
+++ b/scripts/qapi/common.py
@@ -1687,12 +1687,7 @@ class QAPISchemaCommand(QAPISchemaEntity):
             self.arg_type = schema.lookup_type(self._arg_type_name)
             assert isinstance(self.arg_type, QAPISchemaObjectType)
             self.arg_type.check(schema)
-            if self.boxed:
-                if self.arg_type.is_empty():
-                    raise QAPISemError(self.info,
-                                       "Cannot use 'boxed' with empty type")
-            else:
-                assert not self.arg_type.variants
+            assert not self.arg_type.variants or self.boxed
         elif self.boxed:
             raise QAPISemError(self.info, "Use of 'boxed' requires 'data'")
         if self._ret_type_name:
@@ -1721,12 +1716,7 @@ class QAPISchemaEvent(QAPISchemaEntity):
             self.arg_type = schema.lookup_type(self._arg_type_name)
             assert isinstance(self.arg_type, QAPISchemaObjectType)
             self.arg_type.check(schema)
-            if self.boxed:
-                if self.arg_type.is_empty():
-                    raise QAPISemError(self.info,
-                                       "Cannot use 'boxed' with empty type")
-            else:
-                assert not self.arg_type.variants
+            assert not self.arg_type.variants or self.boxed
         elif self.boxed:
             raise QAPISemError(self.info, "Use of 'boxed' requires 'data'")
 
diff --git a/scripts/qapi/events.py b/scripts/qapi/events.py
index b732581046..e0abfef7b0 100644
--- a/scripts/qapi/events.py
+++ b/scripts/qapi/events.py
@@ -65,6 +65,8 @@ def gen_event_send(name, arg_type, boxed, event_enum_name, event_emit):
     # practice, we can rename our local variables with a leading _ prefix,
     # or split the code into a wrapper function that creates a boxed
     # 'param' object then calls another to do the real work.
+    have_args = boxed or (arg_type and not arg_type.is_empty())
+
     ret = mcgen('''
 
 %(proto)s
@@ -73,15 +75,13 @@ def gen_event_send(name, arg_type, boxed, event_enum_name, event_emit):
 ''',
                 proto=build_event_send_proto(name, arg_type, boxed))
 
-    if arg_type and not arg_type.is_empty():
+    if have_args:
         ret += mcgen('''
     QObject *obj;
     Visitor *v;
 ''')
         if not boxed:
             ret += gen_param_var(arg_type)
-    else:
-        assert not boxed
 
     ret += mcgen('''
 
@@ -90,7 +90,7 @@ def gen_event_send(name, arg_type, boxed, event_enum_name, event_emit):
 ''',
                  name=name)
 
-    if arg_type and not arg_type.is_empty():
+    if have_args:
         ret += mcgen('''
     v = qobject_output_visitor_new(&obj);
 ''')
@@ -121,7 +121,7 @@ def gen_event_send(name, arg_type, boxed, event_enum_name, event_emit):
                  event_emit=event_emit,
                  c_enum=c_enum_const(event_enum_name, name))
 
-    if arg_type and not arg_type.is_empty():
+    if have_args:
         ret += mcgen('''
     visit_free(v);
 ''')