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

[Markus Armbruster <armbru@redhat.com>]

Paolo Bonzini <pbonzini@redhat.com> writes:

> From: Marc-André Lureau <marcandre.lureau@redhat.com>
>
> Generate high-level native Rust declarations for the QAPI types.
>
> - char* is mapped to String, scalars to there corresponding Rust types
>
> - enums use #[repr(u32)] and can be transmuted to their C counterparts
>
> - has_foo/foo members are mapped to Option<T>
>
> - lists are represented as Vec<T>
>
> - structures map fields 1:1 to Rust
>
> - alternate are represented as Rust enum, each variant being a 1-element
>   tuple
>
> - unions are represented in a similar way as in C: a struct S with a "u"
>   member (since S may have extra 'base' fields). The discriminant
>   isn't a member of S, since Rust enum already include it, but it can be
>   recovered with "mystruct.u.into()"
>
> Anything that includes a recursive struct puts it in a Box.  Lists are
> not considered recursive, because Vec breaks the recursion (it's possible
> to construct an object containing an empty Vec of its own type).
>
> Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> Link: https://lore.kernel.org/r/20210907121943.3498701-21-marcandre.lureau@redhat.com
> [Paolo: rewrite conversion of schema types to Rust types]
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Please mention how to actually generate Rust, because it's anything but
obvious: pass -B qapi.backend.QAPIRsBackend to qapi-gen.py.  Recommend
to mention it again in the cover letter.

Additionally, state that this is a hack we'll want to replace both in
the commit message and a TODO comment.  See review of v1's cover letter
for why.

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