Hi
On Tue, Jun 19, 2018 at 11:06 AM, Markus Armbruster <arm...@redhat.com> wrote:
> 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().
>
> Drawback: pylint complains. We'll live.
>
>>
>> Suggested-by: Markus Armbruster <arm...@redhat.com>
>> Signed-off-by: Marc-André Lureau <marcandre.lur...@redhat.com>
>> Reviewed-by: Markus Armbruster <arm...@redhat.com>
>
> Shouldn't this be squashed into the previous patch?
I would rather keep it seperate, as it makes reviewing both a bit
easier to me. But feel free to squash on commit.
>
>> ---
>> scripts/qapi/common.py | 21 +++++++++++++++++----
>> 1 file changed, 17 insertions(+), 4 deletions(-)
>>
>> diff --git a/scripts/qapi/common.py b/scripts/qapi/common.py
>> index d8ab3d8f7f..eb07d641ab 100644
>> --- a/scripts/qapi/common.py
>> +++ b/scripts/qapi/common.py
>> @@ -1026,13 +1026,19 @@ class QAPISchemaEntity(object):
>> # such place).
>> self.info = info
>> self.doc = doc
>> - self.ifcond = listify_cond(ifcond)
>> + self._ifcond = ifcond # self.ifcond is set only 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?
There is also implicit object types.
>
>>
>> def is_implicit(self):
>> return not self.info
>> @@ -1169,6 +1175,7 @@ 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)
>> @@ -1201,8 +1208,10 @@ 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)
>> self.ifcond = self.element_type.ifcond
>>
>> def is_implicit(self):
>> @@ -1245,6 +1254,7 @@ 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)
>> @@ -1427,6 +1437,7 @@ 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
>> @@ -1470,6 +1481,7 @@ class QAPISchemaCommand(QAPISchemaEntity):
>> self.allow_oob = allow_oob
>>
>> 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
>> @@ -1504,6 +1516,7 @@ 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
>> @@ -1633,7 +1646,7 @@ 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:1649,29: Access to a protected member _ifcond of a client class
> (protected-access)
>
> Layering violation. Tolerable, I think.
>
yeah, alternative would be to add an assert_ifcond() method in type..?
I'll add a # pylint: disable=protected-access for now
>> self._def_entity(QAPISchemaObjectType(name, info, doc, ifcond,
>> None, members, None))
>> @@ -1679,7 +1692,7 @@ 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)
>
> Perhaps other attributes that become valid only at .check() time should
> receive the same treatment. Not necessarily in this series, not
> necessarily by you. A TODO comment wouldn't hurt, though.
>
It doesn't look obvious to me which should receive the same
treatement. I'll leave that to you to figure out :)
--
Marc-André Lureau
