Re: [PATCH v3 2/3] qapi: Do not generate empty enum

[Markus Armbruster]

Philippe Mathieu-Daudé <philmd@linaro.org> writes:

> Can we meet half-way only generating the MAX definitions for
> unconditional enums, keeping the conditional ones as is?
>
> -- >8 --
> diff --git a/scripts/qapi/types.py b/scripts/qapi/types.py
> @@ -88,16 +88,18 @@ def gen_enum(name: str,
>               members: List[QAPISchemaEnumMember],
>               prefix: Optional[str] = None) -> str:
>      assert members
> -    # append automatically generated _MAX value
> -    enum_members = members + [QAPISchemaEnumMember('_MAX', None)]
> -
>      ret = mcgen('''
>
>  typedef enum %(c_name)s {
>  ''',
>                  c_name=c_name(name))
>
> -    for memb in enum_members:
> +    has_cond = any(memb.ifcond.is_present() for memb in members)
> +    if has_cond:
> +        # append automatically generated _MAX value
> +        members += [QAPISchemaEnumMember('_MAX', None)]
> +
> +    for memb in members:
>          ret += memb.ifcond.gen_if()
>          ret += mcgen('''
>      %(c_enum)s,
> @@ -105,6 +107,13 @@ def gen_enum(name: str,
>                       c_enum=c_enum_const(name, memb.name, prefix))
>          ret += memb.ifcond.gen_endif()
>
> +    if not has_cond:
> +        ret += mcgen('''
> +#define %(c_name)s %(c_length)s
> +''',
> +                     c_name=c_enum_const(name, '_MAX', prefix),
> +                     c_length=len(members))
> +
>      ret += mcgen('''
>  } %(c_name)s;
>  ''',
> ---

I doubt the benefit "we need a silly case FOO__MAX only sometimes" is
worth the special case.

We could generate something like

    #if [last_member's condition]
    #define FOO__MAX (FOO_last_member + 1)
    #elif [second_to_last_member's condition]
    #define FOO__MAX (FOO_second_to_last_member + 1)
    ...
    #else
    #define FOO__MAX (FOO_last_unconditional_member + 1)
    #endif

but whether that is worth the additional complexity seems doubtful, too.