Re: [Qemu-devel] [PATCH v12 22/36] qapi: Don't let implicit enum MAX member collide

[Eric Blake]

On 11/18/2015 06:12 AM, Markus Armbruster wrote:
> Eric Blake <address@hidden> writes:
> 
>> Now that we guarantee the user doesn't have any enum values
>> beginning with a single underscore, we can use that for our
>> own purposes.  Renaming ENUM_MAX to ENUM__MAX makes it obvious
>> that the sentinel is generated.
> 
> The ENUM__MAX are mildly ugly.  If we cared, we could get rid of most or
> all uses.  Right now, I don't.
> 
> Hmm, perhaps these ENUM__MAX are your motivation for rejecting adjacent
> [-_] in the previous patch, to catch clashes like (foolishly named) type
> 'FOO--MAX' with enumeration type 'Foo'.  I acknowledge the clash.

Yes, and that was part of my reasoning on 21/36 - but you've convinced
me to relax that one, so it no longer applies as an argument here.

> However, there are many more clashes we don't attempt to catch,
> e.g. type 'Foo-lookup' with enumeration type 'Foo'.  Perhaps we want to
> build a real fence later, but right now I don't want us to ram in more
> scattered fence laths.
> 
> Might want to say something like "Rejecting enum members named 'MAX' is
> now useless, and will be dropped in the next patch".

Yes, that helps the commit message. Can you handle it, or do I need to
send a fixup?

> 
>> This patch was mostly generated by applying a temporary patch:
>>
>> |diff --git a/scripts/qapi.py b/scripts/qapi.py
>> |index e6d014b..b862ec9 100644
>> |--- a/scripts/qapi.py
>> |+++ b/scripts/qapi.py
>> |@@ -1570,6 +1570,7 @@ const char *const %(c_name)s_lookup[] = {
>> |     max_index = c_enum_const(name, 'MAX', prefix)
>> |     ret += mcgen('''
>> |     [%(max_index)s] = NULL,
>> |+// %(max_index)s
>> | };
>> | ''',
>> |                max_index=max_index)
>>
>> then running:
>>
>> $ cat qapi-{types,event}.c tests/test-qapi-types.c |
>>     sed -n 's,^// \(.*\)MAX,s|\1MAX|\1_MAX|g,p' > list
>> $ git grep -l _MAX | xargs sed -i -f list
>>
>> The only things not generated are the changes in scripts/qapi.py.
>>
>> Signed-off-by: Eric Blake <address@hidden>
> 
> Patch looks good.

The fun part was coming up with the automation, and then making sure it
was reproducible. :)

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

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