[09/17] qapi: Add type.is_empty() helper

Commit Message

Eric Blake Feb. 20, 2016, 12:19 a.m. UTC

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, but
adding a check for variants adds verbosity; in the meantime,
add some asserts in places where we don't handle variants.

More immediately, the new .is_empty() helper will help fix a bug
in qapi-visit in the next patch, where the generator did not
handle an explicit empty type in the same was as a missing type.

No change to generated code.

Signed-off-by: Eric Blake <[e-mail]>

---
v1: add some asserts
Previously posted as part of qapi cleanup subset E:
v9: improve commit message
v8: no change
v7: rebase to context change
v6: new patch
---
 scripts/qapi.py       | 5 +++++
 scripts/qapi-event.py | 7 ++++---
 scripts/qapi-types.py | 2 +-
 3 files changed, 10 insertions(+), 4 deletions(-)

Patch

diff --git a/scripts/qapi.py b/scripts/qapi.py
index 8497777..8a4f952 100644
--- a/scripts/qapi.py
+++ b/scripts/qapi.py
@@ -962,6 +962,7 @@  class QAPISchemaObjectType(QAPISchemaType):
             assert isinstance(self.base, QAPISchemaObjectType)
             self.base.check(schema)
             self.base.check_clash(schema, self.info, seen)
+            assert not self.base.variants
         for m in self.local_members:
             m.check(schema)
             m.check_clash(self.info, seen)
@@ -983,6 +984,10 @@  class QAPISchemaObjectType(QAPISchemaType):
         # See QAPISchema._make_implicit_object_type()
         return self.name[0] == ':'

+    def is_empty(self):
+        assert self.members is not None
+        return not self.members and not self.variants
+
     def c_name(self):
         assert not self.is_implicit()
         return QAPISchemaType.c_name(self)
diff --git a/scripts/qapi-event.py b/scripts/qapi-event.py
index 544ae12..8be3b44 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 +58,8 @@  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():
+        assert not arg_type.variants
         ret += mcgen('''
     qov = qmp_output_visitor_new();
     v = qmp_output_get_visitor(qov);
@@ -88,7 +89,7 @@  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 b68e85a..1eb5622 100644
--- a/scripts/qapi-types.py
+++ b/scripts/qapi-types.py
@@ -90,7 +90,7 @@  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;
 ''')