Re: [PATCH v2 4/4] qapi: expose all schema features to code

["Daniel P. Berrangé" <berrange@redhat.com>]

On Thu, Nov 14, 2024 at 01:48:28PM +0100, Markus Armbruster wrote:
> Daniel P. Berrangé <berrange@redhat.com> writes:
> 
> > This replaces use of the constants from the QapiSpecialFeatures
> > enum, with constants from the auto-generate QapiFeatures enum
> > in qapi-features.h
> >
> > The 'deprecated' and 'unstable' features still have a little bit of
> > special handling, being force defined to be the 1st + 2nd features
> > in the enum, regardless of whether they're used in the schema. This
> > retains compatibility with common code that references the features
> > via the QapiSpecialFeatures constants.
> >
> > Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
> > ---
> >  meson.build              |  1 +
> >  scripts/qapi/commands.py |  1 +
> >  scripts/qapi/features.py | 62 ++++++++++++++++++++++++++++++++++++++++
> >  scripts/qapi/gen.py      |  4 +--
> >  scripts/qapi/main.py     |  2 ++
> >  scripts/qapi/schema.py   | 19 +++++++++++-
> >  scripts/qapi/types.py    |  6 ++--
> >  scripts/qapi/visit.py    |  3 +-
> >  8 files changed, 92 insertions(+), 6 deletions(-)
> >  create mode 100644 scripts/qapi/features.py
> >
> > diff --git a/meson.build b/meson.build
> > index d26690ce20..b9d58be66f 100644
> > --- a/meson.build
> > +++ b/meson.build
> > @@ -3332,6 +3332,7 @@ qapi_gen_depends = [ meson.current_source_dir() / 'scripts/qapi/__init__.py',
> >                       meson.current_source_dir() / 'scripts/qapi/schema.py',
> >                       meson.current_source_dir() / 'scripts/qapi/source.py',
> >                       meson.current_source_dir() / 'scripts/qapi/types.py',
> > +                     meson.current_source_dir() / 'scripts/qapi/features.py',
> >                       meson.current_source_dir() / 'scripts/qapi/visit.py',
> >                       meson.current_source_dir() / 'scripts/qapi-gen.py'
> >  ]
> > diff --git a/scripts/qapi/commands.py b/scripts/qapi/commands.py
> > index d629d2d97e..bf88bfc442 100644
> > --- a/scripts/qapi/commands.py
> > +++ b/scripts/qapi/commands.py
> > @@ -355,6 +355,7 @@ def visit_begin(self, schema: QAPISchema) -> None:
> >  #include "qemu/osdep.h"
> >  #include "%(prefix)sqapi-commands.h"
> >  #include "%(prefix)sqapi-init-commands.h"
> > +#include "%(prefix)sqapi-features.h"
> >  
> >  void %(c_prefix)sqmp_init_marshal(QmpCommandList *cmds)
> >  {
> > diff --git a/scripts/qapi/features.py b/scripts/qapi/features.py
> > new file mode 100644
> > index 0000000000..dc10c7cea0
> > --- /dev/null
> > +++ b/scripts/qapi/features.py
> > @@ -0,0 +1,62 @@
> > +"""
> > +QAPI types generator
> 
> QAPI features generator
> 
> > +
> > +Copyright 2024 Red Hat
> > +
> > +This work is licensed under the terms of the GNU GPL, version 2.
> > +# See the COPYING file in the top-level directory.
> > +"""
> > +
> > +from typing import List, Optional
> 
> pylint gripes

Sigh, I really wish we had pylint/mypy/pycodestyle being run as
part of 'make check' by default. I don't like making the mistake
of sending patches which fail extra non-default checks maintainers
need compliance with.

> 
>     scripts/qapi/features.py:10:0: W0611: Unused List imported from typing (unused-
>     import)
>     scripts/qapi/features.py:10:0: W0611: Unused Optional imported from typing (unused-import)
> 
> > +
> > +from .common import c_enum_const, mcgen, c_name
> 
>     scripts/qapi/features.py:12:0: W0611: Unused mcgen imported from common (unused-import)
> 
> > +from .gen import QAPISchemaMonolithicCVisitor
> > +from .schema import (
> > +    QAPISchema,
> > +    QAPISchemaFeature,
> > +)
> > +from .source import QAPISourceInfo
> 
>     scripts/qapi/features.py:18:0: W0611: Unused QAPISourceInfo imported from source (unused-import)
> 
> > +
> > +
> > +class QAPISchemaGenFeatureVisitor(QAPISchemaMonolithicCVisitor):
> > +
> > +    def __init__(self, prefix: str):
> > +        super().__init__(
> > +            prefix, 'qapi-features',
> > +            ' * Schema-defined QAPI features',
> > +            __doc__)
> > +
> > +        self.features = {}
> 
> mypy gripes
> 
>     scripts/qapi/features.py:29: error: Need type annotation for "features" (hint: "features: Dict[<type>, <type>] = ...")  [var-annotated]
> 
> Elsewhere, we avoid rummaging in QAPISchema's innards by defining
> suitable visit.  If that's too much trouble for you now, I can take this
> as is an clean up on top.
> 
> > +
> > +    def visit_begin(self, schema: QAPISchema):
> 
> mypy gripes
> 
>     scripts/qapi/features.py:31: error: Function is missing a return type annotation  [no-untyped-def]
> 
> > +        self.features = schema._feature_dict
> 
> pylint gripes
> 
>     scripts/qapi/features.py:32:24: W0212: Access to a protected member _feature_dict of a client class (protected-access)
> 
> > +
> > +    def visit_end(self) -> None:
> > +        features = [
> > +            self.features[f]
> > +            for f in QAPISchemaFeature.SPECIAL_NAMES
> > +        ]
> > +
> > +        features.extend(
> > +            sorted(
> > +                filter(lambda f: not f.is_special(),
> > +                       self.features.values()),
> > +                key=lambda f: f.name)
> > +        )
> 
> @features is schema._feature_dict.values() sorted by name in a certain
> way, namely first the .SPECIAL_NAMES in order, then all the others in
> alphabetical order.
> 
> Why you do this is not immediately obvious.  I guess it's to make the
> generated enum a compatible extension of enum QapiSpecialFeature.  That
> one exists for use by schema-independent support code such
> compat_policy_input_ok() and qobject_output_policy_skip().

Yes, I wanted the overlapping enums vaules to match.

> I further guess you sort the non-special features just to make the
> generated code easier for humans to navigate.
> 
> Correct?

The remaining sort was just to give a predictable stable output,
should QAPI usage of features be reordered.

> > +
> > +        self._genh.add("typedef enum {\n")
> > +        for f in features:
> > +            self._genh.add(f"    {c_enum_const('qapi_feature', f.name)}")
> > +            if f.name in QAPISchemaFeature.SPECIAL_NAMES:
> > +                self._genh.add(f" = {c_enum_const('qapi', f.name)},\n" )
> 
> pycodestyle gripes
> 
>     scripts/qapi/features.py:51:71: E202 whitespace before ')'
> 
> > +            else:
> > +                self._genh.add(",\n")
> > +
> > +        self._genh.add("} " + c_name('QapiFeature') + ";\n")
> > +
> 
> pycodestyle gripes
> 
>     scripts/qapi/features.py:57:1: E302 expected 2 blank lines, found 1
> 
> This part generates a C enum.  It's similar to gen_enum() from types.py,
> except we work with a list of QAPISchemaFeature here, and a list of
> QAPISchemaEnumMember there.
> 
> To reuse gen_enum() here, we'd have to make up a member list, like we do
> in events.py for enum QAPIEvent.

I'll have a look at that.

> > diff --git a/scripts/qapi/schema.py b/scripts/qapi/schema.py
> > index e97c978d38..5e14b1829b 100644
> > --- a/scripts/qapi/schema.py
> > +++ b/scripts/qapi/schema.py
> > @@ -933,8 +933,11 @@ def connect_doc(self, doc: Optional[QAPIDoc]) -> None:
> >  class QAPISchemaFeature(QAPISchemaMember):
> >      role = 'feature'
> >  
> > +    # Features which are standardized across all schemas
> > +    SPECIAL_NAMES = ['deprecated', 'unstable']
> > +
> >      def is_special(self) -> bool:
> > -        return self.name in ('deprecated', 'unstable')
> > +        return self.name in QAPISchemaFeature.SPECIAL_NAMES
> >  
> >  
> >  class QAPISchemaObjectTypeMember(QAPISchemaMember):
> > @@ -1138,6 +1141,11 @@ def __init__(self, fname: str):
> >          self._entity_list: List[QAPISchemaEntity] = []
> >          self._entity_dict: Dict[str, QAPISchemaDefinition] = {}
> >          self._module_dict: Dict[str, QAPISchemaModule] = OrderedDict()
> > +        self._feature_dict: Dict[str, QAPISchemaFeature] = {}
> > +
> > +        for f in QAPISchemaFeature.SPECIAL_NAMES:
> > +            self._feature_dict[f] = QAPISchemaFeature(f, "special feature")
> 
> mypy gripes
> 
>     scripts/qapi/schema.py:1147: error: Argument 2 to "QAPISchemaFeature" has incompatible type "str"; expected "Optional[QAPISourceInfo]"  [arg-type]
> 
> We commonly use None as info value for built-in stuff, and that's why
> it's Optional[QAPISourceInfo], not just QAPISourceInfo.

Yeah, not sure what I was thinking here, looking again I
should have passed "None"

> But do we really need to make up some QAPISchemaFeature?  Hmm.  The
> appended patch dumbs down ._feature_dict to a set.

I was following the same pattern as self._entity_dict and
self._module_dict, rather than dumbing down to the bare
minimum needed by my current use case. I don't mind which
strategy we take.

> 
> > +
> >          self._schema_dir = os.path.dirname(fname)
> >          self._make_module(QAPISchemaModule.BUILTIN_MODULE_NAME)
> >          self._make_module(fname)
> > @@ -1258,6 +1266,15 @@ def _make_features(
> >      ) -> List[QAPISchemaFeature]:
> >          if features is None:
> >              return []
> > +
> > +        for f in features:
> > +            feat = QAPISchemaFeature(f['name'], info)
> > +            if feat.name not in self._feature_dict:
> > +                if len(self._feature_dict) == 64:
> > +                    raise Exception("Maximum of 64 schema features is permitted")
> 
> The limit is an implementation restriction.  Okay, we can lift it when
> it bites us.
> 
> However, the reporting is less than nice:
> 
>     $ python scripts/qapi-gen.py -o $$ tests/qapi-schema/features-too-many.json 
>     Traceback (most recent call last):
>       File "/work/armbru/qemu/scripts/qapi-gen.py", line 19, in <module>
>         sys.exit(main.main())
>                  ^^^^^^^^^^^
>       File "/work/armbru/qemu/scripts/qapi/main.py", line 96, in main
>         generate(args.schema,
>       File "/work/armbru/qemu/scripts/qapi/main.py", line 51, in generate
>         schema = QAPISchema(schema_file)
>                  ^^^^^^^^^^^^^^^^^^^^^^^
>       File "/work/armbru/qemu/scripts/qapi/schema.py", line 1155, in __init__
>         self._def_exprs(exprs)
>       File "/work/armbru/qemu/scripts/qapi/schema.py", line 1482, in _def_exprs
>         self._def_struct_type(expr)
>       File "/work/armbru/qemu/scripts/qapi/schema.py", line 1377, in _def_struct_type
>         features = self._make_features(expr.get('features'), info)
>                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>       File "/work/armbru/qemu/scripts/qapi/schema.py", line 1274, in _make_features
>         raise Exception("Maximum of 64 schema features is permitted")
>     Exception: Maximum of 64 schema features is permitted

Is there any better way to approach this error reporting ?

With regards,
Daniel
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