Re: [RFC v3 03/32] scripts/qapi: teach c_param_type() to return const argument type

[Markus Armbruster]

marcandre.lureau@redhat.com writes:

> From: Marc-André Lureau <marcandre.lureau@redhat.com>
>
> The argument isn't owned by the callee, so it better be const.
> But a lot of code in QEMU rely on non-const arguments to tweak it (steal
> values etc).
>
> Since Rust types / bindings are derived from the C version, we have to
> be more accurate there to do correct ownership in the bindings.
>
> Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> ---
>  scripts/qapi/schema.py | 15 +++++++++++----
>  1 file changed, 11 insertions(+), 4 deletions(-)
>
> diff --git a/scripts/qapi/schema.py b/scripts/qapi/schema.py
> index 3d72c7dfc9..1f6301c394 100644
> --- a/scripts/qapi/schema.py
> +++ b/scripts/qapi/schema.py
> @@ -226,8 +226,15 @@ def c_type(self):
>          pass
>  
>      # Return the C type to be used in a parameter list.
> -    def c_param_type(self):
> -        return self.c_type()
> +    #
> +    # The argument should be considered const, since no ownership is given to
> +    # the callee, but qemu C code frequently tweaks it. Set const=True for a
> +    # stricter declaration.

This comment makes sense only if you're familiar with Rust, where "may
change" is actually tied to ownership.

However, I can't see a use of .c_param_type(True).  Sure you need this
patch in this series?

> +    def c_param_type(self, const: bool = False):
> +        c_type = self.c_type()
> +        if const and c_type.endswith(POINTER_SUFFIX):
> +            c_type = 'const ' + c_type
> +        return c_type
>  
>      # Return the C type to be used where we suppress boxing.
>      def c_unboxed_type(self):
> @@ -280,10 +287,10 @@ def c_name(self):
>      def c_type(self):
>          return self._c_type_name
>  
> -    def c_param_type(self):
> +    def c_param_type(self, const: bool = False):
>          if self.name == 'str':
>              return 'const ' + self._c_type_name
> -        return self._c_type_name
> +        return super().c_param_type(const)

Would

       def c_param_type(self, const: bool = False):
           return super().c_param_type(const or self.name == 'str')

do?

>  
>      def json_type(self):
>          return self._json_type_name