Re: [PATCH v2 12/16] scripts/qapi: generate high-level Rust bindings

Markus Armbruster
2026-03-03T12:31:59Z

Paolo Bonzini <pbonzini@redhat.com> writes:

> On 2/25/26 15:39, Markus Armbruster wrote:
>>> +def rs_name(name: str) -> str:
>>> + """
>>> + Map @name to a valid, possibly raw Rust identifier.
>>> + """
>>> + name = re.sub(r'[^A-Za-z0-9_]', '_', name)
>>> + if name[0].isnumeric():
>>
>> .isdigit()? It's what c_name() uses...
>>
>>> + name = '_' + name
>>
>> In review of v1, I pointed to "The Rust Reference"
>>
>> Identifiers starting with an underscore are typically used to
>> indicate an identifier that is intentionally unused, and will
>> silence the unused warning in rustc.
>>
>> https://doc.rust-lang.org/reference/identifiers.html
>>
>> You replied "In this case it doesn't really matter: public items (such
>> as QAPI enum entries, or struct fields) do not raise the unused warning
>> anyway."
>>
>> What gives us confidence rs_name() will only be used where it doesn't
>> really matter?
>
> The fact that all QAPI type definitions are (more or less by design) public.

Any particular reason not to use the same 'q_' prefix as in C?

>>> + # avoid some clashes with the standard library
>>> + if name in ('String',):
>>> + name = 'Qapi' + name
>>
>> This hides the unwise use of 'String' in qapi/net.json from Rust. I'd
>> rather rename that one.
>
> Ok, BoxedString?

Works for me.

>>> +
>>> + return name
>>> +
>>> +
>>> +def to_camel_case(value: str) -> str:
>>> + return ''.join('_' + word if word[0].isdigit()
>>> + else word[:1].upper() + word[1:]
>>> + for word in filter(None, re.split("[-_]+", value)))
>>
>> Please use r'...' for regular expressions always.
>>
>> Why do you need filter()?
>
> To handle - or _ at the beginning or ending of a string, where an empty
> string would cause an IndexError in word[0].isdigit().

Got it, thanks.

>> This maps 'foo-0123-bar' to 'Foo_0123Bar'. Intentional? I'd kind of
>> expect 'Foo0123Bar'.
>
> Will fix (it is meant for 0123-45). New version is:
>
> def to_camel_case(value: str) -> str:
> result = ''
> for p in re.split(r'[-_]+', value):
> if not p:
> pass
> elif p[0].isalpha() or (result and result[-1].isalpha()):
> result += p[0].upper() + p[1:]
> else:
> result += '_' + p
> return result

Maps '0123-45' to '_0123_45'. Is the leading '_' intentional?

>>> +def mcgen(s: str, **kwds: object) -> str:
>>> + s = mcgen_common(s, **kwds)
>>> + return re.sub(r'(?: *\n)+', '\n', s)
>>
>> This eats trailing spaces and blank lines. The latter is a big hammer.
>> Without it, I see unwanted blank lines generated. With it, I see wanted
>> blank lines eaten. For instance:
>
> Ok, I can look into adding rstrip here and there.
>
>>> + except FileNotFoundError:
>>> + pass
>>
>> This runs rustfmt to clean up the generated file. Silently does nothing
>> if we don't have rustfmt.
>>
>> Should we make rustfmt a hard requirement? Please discuss this briefly
>> in the commit message.

I'm fine with not running rustfmt, and I'm fine with running it always
(makes it a hard requirement). Running it sometimes feels like more
trouble than it's worth.

> It's unnecessary, but it does make the output look nicer. If I add
> rstrip, I don't need it.
>
>>> + # Return the Rust type for common use
>>
>> Are the uncommon uses?
>>
>> There are for C types, and that's why we have both .c_type(),
>> .c_param_type(), nad .c_unboxed_type().
>
> Yes, Box<> and Vec<>. They just don't deserve their own function unlike C.

I see.