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>

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('''
 

scripts/qapi/common.py

@@ -1687,12 +1687,7 @@ def check(self, schema):
             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 @@ def check(self, schema):
             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'")
 

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);
 ''')

tests/Makefile.include

@@ -311,7 +311,6 @@ qapi-schema += args-array-empty.json
 qapi-schema += args-array-unknown.json
 qapi-schema += args-bad-boxed.json
 qapi-schema += args-boxed-anon.json
-qapi-schema += args-boxed-empty.json
 qapi-schema += args-boxed-string.json
 qapi-schema += args-int.json
 qapi-schema += args-invalid.json

tests/qapi-schema/args-boxed-empty.err

@@ -1 +0,0 @@
-tests/qapi-schema/args-boxed-empty.json:3: Cannot use 'boxed' with empty type

tests/qapi-schema/args-boxed-empty.exit

@@ -1 +0,0 @@
-1

tests/qapi-schema/args-boxed-empty.json

@@ -1,3 +0,0 @@
-# 'boxed' requires a non-empty type
-{ 'struct': 'Empty', 'data': {} }
-{ 'command': 'foo', 'boxed': true, 'data': 'Empty' }

tests/qapi-schema/qapi-schema-test.json

@@ -149,6 +149,7 @@
 { 'command': 'guest-sync', 'data': { 'arg': 'any' }, 'returns': 'any' }
 { 'command': 'boxed-struct', 'boxed': true, 'data': 'UserDefZero' }
 { 'command': 'boxed-union', 'data': 'UserDefListUnion', 'boxed': true }
+{ 'command': 'boxed-empty', 'boxed': true, 'data': 'Empty1' }
 
 # Smoke test on out-of-band and allow-preconfig-test
 { 'command': 'test-flags-command', 'allow-oob': true, 'allow-preconfig': true }
@@ -181,6 +182,7 @@
   'data': { 'a' : 'EventStructOne', 'b' : 'str', '*c': 'str', '*enum3': 'EnumOne' } }
 { 'event': 'EVENT_E', 'boxed': true, 'data': 'UserDefZero' }
 { 'event': 'EVENT_F', 'boxed': true, 'data': 'UserDefFlatUnion' }
+{ 'event': 'EVENT_G', 'boxed': true, 'data': 'Empty1' }
 
 # test that we correctly compile downstream extensions, as well as munge
 # ticklish names

tests/qapi-schema/qapi-schema-test.out

@@ -221,6 +221,8 @@ command boxed-struct UserDefZero -> None
    gen=True success_response=True boxed=True oob=False preconfig=False
 command boxed-union UserDefListUnion -> None
    gen=True success_response=True boxed=True oob=False preconfig=False
+command boxed-empty Empty1 -> None
+   gen=True success_response=True boxed=True oob=False preconfig=False
 command test-flags-command None -> None
    gen=True success_response=True boxed=False oob=True preconfig=True
 object UserDefOptions
@@ -254,6 +256,8 @@ event EVENT_E UserDefZero
    boxed=True
 event EVENT_F UserDefFlatUnion
    boxed=True
+event EVENT_G Empty1
+   boxed=True
 enum __org.qemu_x-Enum
     member __org.qemu_x-value
 object __org.qemu_x-Base

tests/test-qmp-cmds.c

@@ -97,6 +97,10 @@ void qmp_boxed_union(UserDefListUnion *arg, Error **errp)
 {
 }
 
+void qmp_boxed_empty(Empty1 *arg, Error **errp)
+{
+}
+
 __org_qemu_x_Union1 *qmp___org_qemu_x_command(__org_qemu_x_EnumList *a,
                                               __org_qemu_x_StructList *b,
                                               __org_qemu_x_Union2 *c,