Re: [PATCH v2 07/11] qapi/introspect.py: Unify return type of _make_tree()

[Markus Armbruster]

John Snow <jsnow@redhat.com> writes:

> On 11/16/20 4:46 AM, Markus Armbruster wrote:
>> John Snow <jsnow@redhat.com> writes:
>> 
>>> Returning two different types conditionally can be complicated to
>>> type. Let's always return a tuple for consistency. Prohibit the use of
>>> annotations with dict-values in this circumstance. It can be implemented
>>> later if and when the need for it arises.
>>>
>>> Signed-off-by: John Snow <jsnow@redhat.com>
>>> ---
>>>   scripts/qapi/introspect.py | 21 ++++++++++++---------
>>>   1 file changed, 12 insertions(+), 9 deletions(-)
>>>
>>> diff --git a/scripts/qapi/introspect.py b/scripts/qapi/introspect.py
>>> index 16282f2634b..ef469b6c06e 100644
>>> --- a/scripts/qapi/introspect.py
>>> +++ b/scripts/qapi/introspect.py
>>> @@ -77,14 +77,12 @@
>>>   
>>>   def _make_tree(obj: Union[_DObject, str], ifcond: List[str],
>>>                  extra: Optional[Annotations] = None
>>> -               ) -> TreeValue:
>>> +               ) -> Annotated:
>>>       if extra is None:
>>>           extra = {}
>>>       if ifcond:
>>>           extra['if'] = ifcond
>>> -    if extra:
>>> -        return (obj, extra)
>>> -    return obj
>>> +    return (obj, extra)
>> 
>> Less efficient, but that's okay.
>> 
>
> I have bad news about Python :)

Well played, sir!

>>>   
>>>   
>>>   def _tree_to_qlit(obj: TreeValue,
>>> @@ -98,12 +96,16 @@ def indent(level: int) -> str:
>>>           ifobj, extra = obj
>>>           ifcond = cast(Optional[Sequence[str]], extra.get('if'))
>>>           comment = extra.get('comment')
>>> +
>>> +        msg = "Comments and Conditionals not implemented for dict values"
>>> +        assert not (suppress_first_indent and (ifcond or comment)), msg
>> 
>> What exactly does this assertion guard?
>> 
>
> Something that Eduardo noticed in his review. It's ugly, and I explained 
> it poorly.
>
> We don't support annotations on dict *values*, basically. When this 
> function is called with suppress_first_indent, we know that we are being 
> called to process a dict *value* and not a dict *key*.
>
> What do you do with comments or conditionals on just one half of a key: 
> value pair?
>
> Well, break.

Your @msg is a bit misleading then: it suggests comments and
conditionals are not implemented for dict values, but could be.  Not
true for conditionals.

Minimally invasive patch correction: drop @msg.

But the actual impossibility to guard against is even simpler, I
believe:

          if isinstance(obj, tuple):
              assert not suppress_first_indent

But^2, I figure this can be made truly impossible: factor out the part
of _tree_to_qlit() that deals with non-tuple @obj into its own function
(the conditional at its end), then use that for the dict values.

>>> +
>>>           ret = ''
>>>           if comment:
>>>               ret += indent(level) + '/* %s */\n' % comment
>>>           if ifcond:
>>>               ret += gen_if(ifcond)
>>> -        ret += _tree_to_qlit(ifobj, level)
>>> +        ret += _tree_to_qlit(ifobj, level, suppress_first_indent)
>> 
>> Why do you need to pass on @suppress_first_indent now?
>> 
>
> We either never should or we always should have. This is just in the 
> case that "suppress first indent" is used on an annotated node. Which, 
> err, for the annotations we actually support right now (comment, ifcond) 
> -- we will reject in this case.
>
> But it felt precarious...

I suspect the factoring I suggested above will make this less
precarious, too.

>>>           if ifcond:
>>>               ret += '\n' + gen_endif(ifcond)
>>>           return ret
>>> @@ -152,7 +154,7 @@ def __init__(self, prefix: str, unmask: bool):
>>>               ' * QAPI/QMP schema introspection', __doc__)
>>>           self._unmask = unmask
>>>           self._schema: Optional[QAPISchema] = None
>>> -        self._trees: List[TreeValue] = []
>>> +        self._trees: List[Annotated] = []
>>>           self._used_types: List[QAPISchemaType] = []
>>>           self._name_map: Dict[str, str] = {}
>>>           self._genc.add(mcgen('''
>>> @@ -219,7 +221,8 @@ def _use_type(self, typ: QAPISchemaType) -> str:
>>>   
>>>       @classmethod
>>>       def _gen_features(cls,
>>> -                      features: List[QAPISchemaFeature]) -> 
>>> List[TreeValue]:
>>> +                      features: List[QAPISchemaFeature]
>>> +                      ) -> List[Annotated]:
>>>           return [_make_tree(f.name, f.ifcond) for f in features]
>>>   
>>>       def _gen_tree(self, name: str, mtype: str, obj: _DObject,
>>> @@ -239,7 +242,7 @@ def _gen_tree(self, name: str, mtype: str, obj: 
>>> _DObject,
>>>           self._trees.append(_make_tree(obj, ifcond, extra))
>>>   
>>>       def _gen_member(self,
>>> -                    member: QAPISchemaObjectTypeMember) -> TreeValue:
>>> +                    member: QAPISchemaObjectTypeMember) -> Annotated:
>>>           obj: _DObject = {
>>>               'name': member.name,
>>>               'type': self._use_type(member.type)
>>> @@ -255,7 +258,7 @@ def _gen_variants(self, tag_name: str,
>>>           return {'tag': tag_name,
>>>                   'variants': [self._gen_variant(v) for v in variants]}
>>>   
>>> -    def _gen_variant(self, variant: QAPISchemaVariant) -> TreeValue:
>>> +    def _gen_variant(self, variant: QAPISchemaVariant) -> Annotated:
>>>           obj: _DObject = {
>>>               'case': variant.name,
>>>               'type': self._use_type(variant.type)