Re: [PATCH 08/12] qapi/schema: make QAPISourceInfo mandatory

[John Snow]

On 12/16/20 5:18 AM, Markus Armbruster wrote:
> John Snow <jsnow@redhat.com> writes:
>
> > --
> >
> > events.py had an info to route, was it by choice that it wasn't before?
>
> See below.
>
> I figure this is intentionally below the -- line, but ...
>
> > Signed-off-by: John Snow <jsnow@redhat.com>
>
> ... this should be above it.

Script failure. Or human failure, because I used '--' instead of '---'.

> > ---
> >   scripts/qapi/events.py |  2 +-
> >   scripts/qapi/schema.py | 23 +++++++++++++----------
> >   scripts/qapi/types.py  |  9 +++++----
> >   scripts/qapi/visit.py  |  6 +++---
> >   4 files changed, 22 insertions(+), 18 deletions(-)
> >
> > diff --git a/scripts/qapi/events.py b/scripts/qapi/events.py
> > index 9851653b9d11..9ba4f109028d 100644
> > --- a/scripts/qapi/events.py
> > +++ b/scripts/qapi/events.py
> > @@ -225,7 +225,7 @@ def visit_event(self,
> >                                             self._event_emit_name))
> >           # Note: we generate the enum member regardless of @ifcond, to
> >           # keep the enumeration usable in target-independent code.
> > -        self._event_enum_members.append(QAPISchemaEnumMember(name, None))
> > +        self._event_enum_members.append(QAPISchemaEnumMember(name, info))
>
> We pass None because errors should never happen, and None makes that
> quite clear.

Not clear: *why* should errors never happen? This is the only place we 
pass None for SourceInfo that isn't explicitly a literal built-in type. 
This is not obvious.

> We don't actually have a built-in QAPISchemaEnumType for the event enum.
> We merely generate a C enum QAPIEvent along with macro QAPIEvent_str(),
> by passing self._event_emit_name, self._event_enum_members straight to
> gen_enum() and gen_enum_lookup().
>
> If we did build a QAPISchemaEnumType, and used it to diagnose clashes,
> then clashes would be reported like
>
>      mumble.json: In event 'A-B':
>      mumble.json: 2: value 'A-B' collides with value 'A_B'
>
> leaving you guessing what "value" means, and where 'A_B' may be.
>
> Bug: we don't diagnose certain event name clashes.  I'll fix it.

Not clear to me: If I want interface consistency, what *should* be 
passed downwards as the info? it's not quite a builtin as much as it is 
an inferred enum, so should I just ... leave it like this, or wait for 
you to offer a better fix?

> >   
> >   
> >   def gen_events(schema: QAPISchema,
> > diff --git a/scripts/qapi/schema.py b/scripts/qapi/schema.py
> > index 720449feee4d..d5f19732b516 100644
> > --- a/scripts/qapi/schema.py
> > +++ b/scripts/qapi/schema.py
> > @@ -23,6 +23,7 @@
> >   from .error import QAPIError, QAPISemError
> >   from .expr import check_exprs
> >   from .parser import QAPISchemaParser
> > +from .source import QAPISourceInfo
> >   
> >   
> >   class QAPISchemaEntity:
> > @@ -36,10 +37,10 @@ def __init__(self, name, info, doc, ifcond=None, 
> > features=None):
> >           self.name = name
> >           self._module = None
> >           # For explicitly defined entities, info points to the (explicit)
> > -        # definition.  For builtins (and their arrays), info is None.
> > -        # For implicitly defined entities, info points to a place that
> > -        # triggered the implicit definition (there may be more than one
> > -        # such place).
> > +        # definition.  For builtins (and their arrays), info is a null-object
> > +        # sentinel that evaluates to False. For implicitly defined entities,
> > +        # info points to a place that triggered the implicit definition
> > +        # (there may be more than one such place).
>
> s/builtins/built-in types/
>
> The meaning of "a null object sentinel" is less than clear.  Perhaps "a
> special object".

OK.

> >           self.info = info
> >           self.doc = doc
> >           self._ifcond = ifcond or []
> > @@ -209,7 +210,7 @@ class QAPISchemaBuiltinType(QAPISchemaType):
> >       meta = 'built-in'
> >   
> >       def __init__(self, name, json_type, c_type):
> > -        super().__init__(name, None, None)
> > +        super().__init__(name, QAPISourceInfo.builtin(), None)
> >           assert not c_type or isinstance(c_type, str)
> >           assert json_type in ('string', 'number', 'int', 'boolean', 'null',
> >                                'value')
> > @@ -871,7 +872,7 @@ def resolve_type(self, name, info, what):
> >           return typ
> >   
> >       def _module_name(self, fname):
> > -        if fname is None:
> > +        if not fname:
> >               return None
> >           return os.path.relpath(fname, self._schema_dir)
> >   
>
> Sure this hunk belongs to this patch?

Accident.

"info and info.fname" does not behave the same with a falsey info object 
as it does when info was genuinely None; I compensated for that *here*, 
but I should have compensated for it elsewhere.

> > @@ -897,9 +898,11 @@ def _def_builtin_type(self, name, json_type, c_type):
> >           # be nice, but we can't as long as their generated code
> >           # (qapi-builtin-types.[ch]) may be shared by some other
> >           # schema.
> > -        self._make_array_type(name, None)
> > +        self._make_array_type(name, QAPISourceInfo.builtin())
> >   
> >       def _def_predefineds(self):
> > +        info = QAPISourceInfo.builtin()
> > +
>
> Everything else gets its very own copy of the "no source info" object,
> except for the stuff defined here, which gets to share one.  Isn't that
> odd?

It's also the only function where we define so many built-ins in the 
same place, so spiritually they do have the same SourceInfo, right? :)

(OK, no, it wasn't a conscious design choice, but it also seems 
harmless. I am going to assume you'd prefer I not do this?)

> >           for t in [('str',    'string',  'char' + POINTER_SUFFIX),
> >                     ('number', 'number',  'double'),
> >                     ('int',    'int',     'int64_t'),
> > @@ -917,15 +920,15 @@ def _def_predefineds(self):
> >                     ('null',   'null',    'QNull' + POINTER_SUFFIX)]:
> >               self._def_builtin_type(*t)
> >           self.the_empty_object_type = QAPISchemaObjectType(
> > -            'q_empty', None, None, None, None, None, [], None)
> > +            'q_empty', info, None, None, None, None, [], None)
> >           self._def_entity(self.the_empty_object_type)
> >   
> >           qtypes = ['none', 'qnull', 'qnum', 'qstring', 'qdict', 'qlist',
> >                     'qbool']
> >           qtype_values = self._make_enum_members(
> > -            [{'name': n} for n in qtypes], None)
> > +            [{'name': n} for n in qtypes], info)
> >   
> > -        self._def_entity(QAPISchemaEnumType('QType', None, None, None, None,
> > +        self._def_entity(QAPISchemaEnumType('QType', info, None, None, None,
> >                                               qtype_values, 'QTYPE'))
> >   
> >       def _make_features(self, features, info):
> > diff --git a/scripts/qapi/types.py b/scripts/qapi/types.py
> > index 2b4916cdaa1b..a3a16284006b 100644
> > --- a/scripts/qapi/types.py
> > +++ b/scripts/qapi/types.py
> > @@ -71,7 +71,8 @@ def gen_enum(name: str,
> >                members: List[QAPISchemaEnumMember],
> >                prefix: Optional[str] = None) -> str:
> >       # append automatically generated _MAX value
> > -    enum_members = members + [QAPISchemaEnumMember('_MAX', None)]
> > +    enum_members = members + [
> > +        QAPISchemaEnumMember('_MAX', QAPISourceInfo.builtin())]
> >   
> >       ret = mcgen('''
> >   
> > @@ -306,7 +307,7 @@ def _gen_type_cleanup(self, name: str) -> None:
> >   
> >       def visit_enum_type(self,
> >                           name: str,
> > -                        info: Optional[QAPISourceInfo],
> > +                        info: QAPISourceInfo,
> >                           ifcond: List[str],
> >                           features: List[QAPISchemaFeature],
> >                           members: List[QAPISchemaEnumMember],
> > @@ -317,7 +318,7 @@ def visit_enum_type(self,
> >   
> >       def visit_array_type(self,
> >                            name: str,
> > -                         info: Optional[QAPISourceInfo],
> > +                         info: QAPISourceInfo,
> >                            ifcond: List[str],
> >                            element_type: QAPISchemaType) -> None:
> >           with ifcontext(ifcond, self._genh, self._genc):
> > @@ -327,7 +328,7 @@ def visit_array_type(self,
> >   
> >       def visit_object_type(self,
> >                             name: str,
> > -                          info: Optional[QAPISourceInfo],
> > +                          info: QAPISourceInfo,
> >                             ifcond: List[str],
> >                             features: List[QAPISchemaFeature],
> >                             base: Optional[QAPISchemaObjectType],
> > diff --git a/scripts/qapi/visit.py b/scripts/qapi/visit.py
> > index 339f1521524c..3f49c307c566 100644
> > --- a/scripts/qapi/visit.py
> > +++ b/scripts/qapi/visit.py
> > @@ -336,7 +336,7 @@ def _begin_user_module(self, name: str) -> None:
> >   
> >       def visit_enum_type(self,
> >                           name: str,
> > -                        info: QAPISourceInfo,
> > +                        info: Optional[QAPISourceInfo],
> >                           ifcond: List[str],
> >                           features: List[QAPISchemaFeature],
> >                           members: List[QAPISchemaEnumMember],
> > @@ -347,7 +347,7 @@ def visit_enum_type(self,
> >   
> >       def visit_array_type(self,
> >                            name: str,
> > -                         info: Optional[QAPISourceInfo],
> > +                         info: QAPISourceInfo,
> >                            ifcond: List[str],
> >                            element_type: QAPISchemaType) -> None:
> >           with ifcontext(ifcond, self._genh, self._genc):
> > @@ -356,7 +356,7 @@ def visit_array_type(self,
> >   
> >       def visit_object_type(self,
> >                             name: str,
> > -                          info: Optional[QAPISourceInfo],
> > +                          info: QAPISourceInfo,
> >                             ifcond: List[str],
> >                             features: List[QAPISchemaFeature],
> >                             base: Optional[QAPISchemaObjectType],