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

[John Snow]

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 :)

> >   
> >   
> >   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.

> > +
> >           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...

> >           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)