Re: [PATCH v2] qapi: pluggable backend code generators

[Markus Armbruster <armbru@redhat.com>]

Markus Armbruster <armbru@redhat.com> writes:

> Daniel P. Berrangé <berrange@redhat.com> writes:
>
>> The 'qapi.backend.QAPIBackend' class defines an API contract for code
>> generators. The current generator is put into a new class
>> 'qapi.backend.QAPICBackend' and made to be the default impl.
>>
>> A custom generator can be requested using the '-k' arg which takes a
>
> Missed an instance of -k.  Can fix this myself.
>
>> fully qualified python class name
>>
>>    qapi-gen.py -B the.python.module.QAPIMyBackend
>>
>> This allows out of tree code to use the QAPI generator infrastructure
>> to create new language bindings for QAPI schemas. This has the caveat
>> that the QAPI generator APIs are not guaranteed stable, so consumers
>> of this feature may have to update their code to be compatible with
>> future QEMU releases.
>>
>> Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

[...]

>> diff --git a/scripts/qapi/main.py b/scripts/qapi/main.py
>> index 324081b9fc..8a8b1e0121 100644
>> --- a/scripts/qapi/main.py
>> +++ b/scripts/qapi/main.py

[...]

>> @@ -29,32 +25,37 @@ def invalid_prefix_char(prefix: str) -> Optional[str]:
>>      return None
>>  
>>  
>> -def generate(schema_file: str,
>> -             output_dir: str,
>> -             prefix: str,
>> -             unmask: bool = False,
>> -             builtins: bool = False,
>> -             gen_tracing: bool = False) -> None:
>> -    """
>> -    Generate C code for the given schema into the target directory.
>> +def create_backend(path: str) -> QAPIBackend:
>> +    if path is None:
>> +        return QAPICBackend()
>>  
>> -    :param schema_file: The primary QAPI schema file.
>> -    :param output_dir: The output directory to store generated code.
>> -    :param prefix: Optional C-code prefix for symbol names.
>> -    :param unmask: Expose non-ABI names through introspection?
>> -    :param builtins: Generate code for built-in types?
>> +    if "." not in path:
>> +        print(f"Missing qualified module path in '{path}'", file=sys.stderr)
>> +        sys.exit(1)
>>  
>> -    :raise QAPIError: On failures.
>> -    """
>> -    assert invalid_prefix_char(prefix) is None
>> +    module_path, _, class_name = path.rpartition('.')
>
> I'd like to tweak this to
>
>        module_path, dot, class_name = path.rpartition('.')
>        if not dot:
>            print(f"argument of -B must be of the form MODULE.CLASS",
>                  file=sys.stderr)

This bothers flake8:

    scripts/qapi/main.py:34:15: F541 f-string is missing placeholders

I'll make it a plain string instead.

>            sys.exit(1)
>

[...]