Re: [PATCH v3 15/19] scripts/qapi: generate high-level Rust bindings

[Zhao Liu <zhao1.liu@intel.com>]

On Tue, May 26, 2026 at 07:56:14PM +0200, Paolo Bonzini wrote:
> Date: Tue, 26 May 2026 19:56:14 +0200
> From: Paolo Bonzini <pbonzini@redhat.com>
> Subject: [PATCH v3 15/19] scripts/qapi: generate high-level Rust bindings
> X-Mailer: git-send-email 2.54.0
> 
> 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).
> 
> Given the experimental nature of Rust, and the incompleteness of the
> backend (it lacks commands and events), QAPIRsBackend is not modular
> and is not built together with the C and trace-event files.  It can
> be used by specifying "-B qapi.backend.QAPIRsBackend" on the qapi-gen
> command line.
> 
> 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 leaf types]
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  meson.build              |   4 +-
>  scripts/qapi/backend.py  |  25 +++
>  scripts/qapi/common.py   |  49 ++++++
>  scripts/qapi/rs.py       |  50 ++++++
>  scripts/qapi/rs_types.py | 372 +++++++++++++++++++++++++++++++++++++++
>  scripts/qapi/schema.py   |  59 +++++--
>  6 files changed, 540 insertions(+), 19 deletions(-)
>  create mode 100644 scripts/qapi/rs.py
>  create mode 100644 scripts/qapi/rs_types.py

[snip]

> +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():
> +        name = '_' + name
> +    # based from the list:
> +    # https://doc.rust-lang.org/reference/keywords.html
> +    if name in ('Self', 'abstract', 'as', 'async',
                    ^^^^
> +                'await', 'become', 'box', 'break',
> +                'const', 'continue', 'crate', 'do',
                                         ^^^^^
> +                'dyn', 'else', 'enum', 'extern',
> +                'false', 'final', 'fn', 'for',
> +                'if', 'impl', 'in', 'let',
> +                'loop', 'macro', 'match', 'mod',
> +                'move', 'mut', 'override', 'priv',
> +                'pub', 'ref', 'return', 'self',
                                            ^^^^
> +                'static', 'struct', 'super', 'trait',
                                        ^^^^^
> +                'true', 'try', 'type', 'typeof',
> +                'union', 'unsafe', 'unsized', 'use',
> +                'virtual', 'where', 'while', 'yield'):
> +        name = 'r#' + name

EMM, r#self, r#Self, r#crate and r#super are "RESERVED_RAW_IDENTIFIER",
and "It is an error to use the RESERVED_RAW_IDENTIFIER token". [*]

[*]: https://doc.rust-lang.org/reference/identifiers.html#grammar-RESERVED_RAW_IDENTIFIER

We can't use 'q_' prefix for these special case, or what about
name + '_'?

e.g.,

if name in ('self', 'Self', 'crate', 'super'):
   name = name + '_'
elif name in (...)
   name = 'r#' + name

> +
> +    return name
> +

[snip]

> @@ -502,6 +515,9 @@ def is_implicit(self) -> bool:
>      def c_type(self) -> str:
>          return c_name(self.name) + POINTER_SUFFIX
>  
> +    def rs_type(self) -> str:

Only a nit, it's better to check _checked before accessing element_type
(just refer Markus' suggestion in v2)

assert self._checked

> +        return 'Vec<%s>' % self.element_type.rs_type()
> +

Regards,
Zhao