Re: [PATCH 00/19] rust: QObject and QAPI bindings

[Markus Armbruster <armbru@redhat.com>]

Paolo Bonzini <pbonzini@redhat.com> writes:

> On 12/9/25 07:01, Markus Armbruster wrote:
>> Markus Armbruster <armbru@redhat.com> writes:
>> 
>>> I applied, ran make, and it didn't create qapi-types.rs and
>>> test-qapi-types.rs for me.  What am I missing?
>> 
>> Looks like I have to run with -B qapi.backend.QAPIRsBackend.
>> 
>> -B is meant for out-of-tree backends.  Commit dde279925c9 explains:
>> 
>>      qapi: pluggable backend code generators
>>      
>>      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
>>      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.
>> 
>> Using it for the in-tree Rust backend is fine for a prototype.
>> Mentioning it in a commit message or the cover letter would've saved me
>> some digging.
>
> Well, it wasn't intentional - right now it does this:
>
> test_qapi_rs_files = custom_target('QAPI Rust',
>    output: 'test-qapi-types.rs',
>    input: [ files(meson.project_source_root() + 
> '/tests/qapi-schema/qapi-schema-test.json') ],
>    command: [ qapi_gen, '-o', meson.current_build_dir(), '-b', 
> '@INPUT0@', '-B', 'qapi.backend.QAPIRsBackend', '-p', 'test-' ],
>    depend_files: [ qapi_inputs, qapi_gen_depends ])
>
> so "make rust/tests/test-qapi-types.rs" will work, and so will "make" if 
> you have --enable-rust.
>
> Let us know what you'd prefer and we'll switch.  Alternatively, 
> retconning -B's meaning so that it applies to Rust will work too. :)

Any particular reason *not* to generate Rust unconditionally along with
C?

To do it, stick gen_rs_types() into QAPICodeBackend.generate().  Then
the build runs qapi-gen at most once[*].



[*] Lie.  Sphinx runs the *frontend* another time.