Second thoughts...
Marc-André Lureau <marcandre.lur...@redhat.com> writes:
> We commonly initialize attributes to None in .init(), then set their
> real value in .check(). Accessing the attribute before .check()
> yields None. If we're lucky, the code that accesses the attribute
> prematurely chokes on None.
>
> It won't for .ifcond, because None is a legitimate value.
>
> Leave the ifcond attribute undefined until check().
>
> Suggested-by: Markus Armbruster <arm...@redhat.com>
> Signed-off-by: Marc-André Lureau <marcandre.lur...@redhat.com>
> ---
> scripts/qapi.py | 21 +++++++++++++++++----
> 1 file changed, 17 insertions(+), 4 deletions(-)
>
> diff --git a/scripts/qapi.py b/scripts/qapi.py
> index 8f54dead8d..4d2c214f19 100644
> --- a/scripts/qapi.py
> +++ b/scripts/qapi.py
> @@ -1011,13 +1011,19 @@ class QAPISchemaEntity(object):
> # such place).
> self.info = info
> self.doc = doc
> - self.ifcond = listify_cond(ifcond)
> + self._ifcond = ifcond # self.ifcond is set after check()
>
> def c_name(self):
> return c_name(self.name)
>
> def check(self, schema):
> - pass
> + if isinstance(self._ifcond, QAPISchemaType):
> + # inherit the condition from a type
> + typ = self._ifcond
> + typ.check(schema)
> + self.ifcond = typ.ifcond
> + else:
> + self.ifcond = listify_cond(self._ifcond)
Whenever we add a .check(), we need to prove QAPISchema.check()'s
recursion still terminates, and terminates the right way.
Argument before this patch: we recurse only into types contained in
types, e.g. an object type's base type, and we detect and report cycles
as "Object %s contains itself", in QAPISchemaObjectType.check().
The .check() added here recurses into a type. If this creates a cycle,
it'll be caught and reported as "contains itself". We still need to
show that the error message remains accurate.
We .check() here to inherit .ifcond from a type. As far as I can tell,
we use this inheritance feature only to inherit an array's condition
from its element type. That's safe, because an array does contain its
elements.
This is hardly a rigorous proof. Just enough to make me believe your
code works.
However, I suspect adding the inheritance feature at the entity level
complicates the correctness argument without real need. Can we restrict
it to array elements? Have QAPISchemaArrayType.check() resolve
type-valued ._ifcond, and all the others choke on it?
>
> def is_implicit(self):
> return not self.info
> @@ -1138,6 +1144,7 @@ class QAPISchemaEnumType(QAPISchemaType):
> self.prefix = prefix
>
> def check(self, schema):
> + QAPISchemaType.check(self, schema)
> seen = {}
> for v in self.values:
> v.check_clash(self.info, seen)
> @@ -1170,8 +1177,10 @@ class QAPISchemaArrayType(QAPISchemaType):
> self.element_type = None
>
> def check(self, schema):
> + QAPISchemaType.check(self, schema)
> self.element_type = schema.lookup_type(self._element_type_name)
> assert self.element_type
> + self.element_type.check(schema)
This .check is locally obvious: an array contains its elements.
> self.ifcond = self.element_type.ifcond
>
> def is_implicit(self):
> @@ -1214,6 +1223,7 @@ class QAPISchemaObjectType(QAPISchemaType):
> self.members = None
>
> def check(self, schema):
> + QAPISchemaType.check(self, schema)
> if self.members is False: # check for cycles
> raise QAPISemError(self.info,
> "Object %s contains itself" % self.name)
> @@ -1396,6 +1406,7 @@ class QAPISchemaAlternateType(QAPISchemaType):
> self.variants = variants
>
> def check(self, schema):
> + QAPISchemaType.check(self, schema)
> self.variants.tag_member.check(schema)
> # Not calling self.variants.check_clash(), because there's nothing
> # to clash with
> @@ -1438,6 +1449,7 @@ class QAPISchemaCommand(QAPISchemaEntity):
> self.boxed = boxed
>
> def check(self, schema):
> + QAPISchemaEntity.check(self, schema)
> if self._arg_type_name:
> self.arg_type = schema.lookup_type(self._arg_type_name)
> assert (isinstance(self.arg_type, QAPISchemaObjectType) or
> @@ -1471,6 +1483,7 @@ class QAPISchemaEvent(QAPISchemaEntity):
> self.boxed = boxed
>
> def check(self, schema):
> + QAPISchemaEntity.check(self, schema)
> if self._arg_type_name:
> self.arg_type = schema.lookup_type(self._arg_type_name)
> assert (isinstance(self.arg_type, QAPISchemaObjectType) or
> @@ -1589,7 +1602,7 @@ class QAPISchema(object):
> # But it's not tight: the disjunction need not imply it. We
> # may end up compiling useless wrapper types.
> # TODO kill simple unions or implement the disjunction
> - assert ifcond == typ.ifcond
> + assert ifcond == typ._ifcond
pylint complains
W:1605,29: Access to a protected member _ifcond of a client class
(protected-access)
Layering violation. Tolerable, I think.
> else:
> self._def_entity(QAPISchemaObjectType(name, info, doc, ifcond,
> None, members, None))
> @@ -1635,7 +1648,7 @@ class QAPISchema(object):
> assert len(typ) == 1
> typ = self._make_array_type(typ[0], info)
> typ = self._make_implicit_object_type(
> - typ, info, None, self.lookup_type(typ).ifcond,
> + typ, info, None, self.lookup_type(typ),
> 'wrapper', [self._make_member('data', typ, info)])
> return QAPISchemaObjectTypeVariant(case, typ)
