[PATCH wayland] Add "enum" attribute to "arg" elements

Giulio Camuffo giuliocamuffo at gmail.com
Wed Sep 3 00:28:30 PDT 2014

2014-09-03 10:15 GMT+03:00 Pekka Paalanen <ppaalanen at gmail.com>:
> On Mon, 1 Sep 2014 22:07:44 +0200
> "Nils Chr. Brause" <nilschrbrause at gmail.com> wrote:
>> On Mon, Sep 1, 2014 at 10:45 AM, Pekka Paalanen <ppaalanen at gmail.com> wrote:
>> > Another problem with this patch is that while it adds new syntax to the
>> > protocol XML, it does not add anything that would either explain nor
>> > validate/enforce it. (We do not actually use the DTD for anything
>> > anymore.)
>> >
>> > Yes, we do not have a document describing the XML format, and that is a
>> > problem. Would be nice to start one, if anyone can work with Publican.
>> >
>> > The very least, wayland-scanner should be reading the enum attribute
>> > and check that the referenced enum exists. I'm not sure if it can
>> > generate a nice doc snippet into the generated code, but if there is a
>> > way to include that, it would be useful. We need *something* in the
>> > Wayland repository actually using these new attributes, so that they do
>> > not bit-rot immediately.
>> I will look into the scanner code then. That is probably the easiest
>> possibility
>> to prevent bit-rot, since I never did anything with Publican.
>> While I'm at that, I would also like to make use of the enum names in the
>> generated C code. As far as I can see, this would not break any existing
>> code, would it? Also, that would require the enum definitions to be at the
>> top
>> of the header files (just below the struct forward declarations), because
>> enums cannot be forward declared. Would that be acceptable?
> Perhaps, if it does not cause problems on C++. I'm not sure, but I
> recall C++ being more strict than C wrt. enums.

It is, in the sense that it doesn't automatically cast int to enums,
so that could break the API. Also, wouldn't it possibily be an ABI
break? Afaik enums don't have a very defined size, so what is now a
int32 could become e.g. a 16 bits enum field.


> I do not believe we can change the XML format so that some <enum>
> elements would become <bitfield> instead. Existing generators would
> probably ignore <bitfield> and we need to keep the XML format stable.
> Considering all that, I'm not really sure that supporting strictly
> typed languages is worth the effort. After all, this API is for toolkit
> developers, and app developers will be using toolkit APIs, not this.
> Thanks,
> pq
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