Re: [PATCH 08/28] qapi: Support flat unions tag values with leading digit

[Markus Armbruster <armbru@redhat.com>]

Markus Armbruster <armbru@redhat.com> writes:

> John Snow <jsnow@redhat.com> writes:
>
>> On 3/23/21 5:40 AM, Markus Armbruster wrote:
>>> Flat union tag values get checked twice: as enum member name, and as
>>> union branch name.  The former accepts leading digits, the latter
>>> doesn't.  The restriction feels arbitrary.  Skip the latter check.
>>>
>>> This can expose c_name() to input it can't handle: a name starting
>>> with a digit.  Improve it to return a valid C identifier for any
>>> input.
>>>
>>> Signed-off-by: Markus Armbruster <armbru@redhat.com>
>>
>> Anything in particular inspire this?
>
> Just a desire for keeping things simple.  "Any enum type works as
> discriminator" is simpler than "any enum works, but branches
> corresponding to enum values starting with a digit cannot have members".
> Let me elaborate.
>
> This works:
>
>     {'enum': 'Enu', 'data': ['0', 'eins', '2']}
>     {'struct': 'St', 'data': {'s': 'str'}}
>     {'union': 'Uni',
>      'base': {'type': 'Enu'},
>      'discriminator': 'type',
>      'data': {
>        'eins': 'St'}}
>
> But if you change the last line to
>
>        '0': 'St'}}
>
> you get told off:
>
>     scripts/qapi-gen.py: /dev/stdin: In union 'Uni':
>     /dev/stdin:3: 'data' member '0' has an invalid name

Improved commit message:

    qapi: Permit flat union members for any tag value

    Flat union branch names match the tag enum's member names.  Omitted
    branches default to "no members for this tag value".

    Branch names starting with a digit get rejected like "'data' member
    '0' has an invalid name".  However, omitting the branch works.

    This is because flat union tag values get checked twice: as enum
    member name, and as union branch name.  The former accepts leading
    digits, the latter doesn't.

    Branches whose names start with a digit therefore cannot have members.
    Feels wrong.  Get rid of the restriction by skipping the latter check.

    This can expose c_name() to input it can't handle: a name starting
    with a digit.  Improve it to return a valid C identifier for any
    input.

    Signed-off-by: Markus Armbruster <armbru@redhat.com>

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