Re: [Qemu-devel] [PATCH v11 23/24] qapi: Reserve 'u' member name

[Eric Blake]

On 10/27/2015 02:21 AM, Markus Armbruster wrote:
> Eric Blake <address@hidden> writes:
> 
>> Now that we have separated union tag values from colliding with
>> non-variant C names, by naming the union 'u', we should reserve
>> this name for our use.  Note that we want to forbid 'u' even in
>> a struct with no variants, because it is possible for a future
>> qemu release to extend QMP in a backwards-compatible manner while
>> converting from a struct to a flat union.  Fortunately, no
>> existing clients were using this member name.  If we ever find
>> the need for QMP to have a member 'u', we could at that time
>> relax things, perhaps by having c_name() munge the QMP member to
>> 'q_u'.
>>
>> Note that we cannot forbid 'u' everywhere (by adding the
>> rejection code to check_name()), because the existing QKeyCode
>> enum already uses it; therefore we only reserve it as a struct
>> type member name.
>>
>> Signed-off-by: Eric Blake <address@hidden>
>>
>> ---
>> v11: commit message tweaks, use c_name(), tweak test names

>> -        if c_name(key).startswith('has_'):
>> +        if c_name(key, False) == 'u' or c_name(key).startswith('has_'):
> 
> Slightly odd: new c_name() has protect=False, the existing one doesn't.
> While we don't really need protect=False, it feels a bit cleaner.  If
> you like, I can add it to the existing one when it gets added in PATCH
> 05.

You're right - either both places need it, or neither place does.
Argument _for_ using c_name(, False): that's what we do in check_name()
when looking for 'q_', because we have to (if we use the default
c_name(, True), then the name gets munged and starts with q_ even though
the original did not).  So even though we don't munge 'u' or 'has_' now,
if c_name() starts munging them in the future, consistently using
c_name(, False) here will protect us.  So yes, make the change in patch 5.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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