[PATCH wayland 2/2] scanner: Generate all SINCE_VERSION macros for everyone

[Pekka Paalanen]

On Wed, 10 Aug 2016 14:47:06 +0200
Quentin Glidic <sardemff7+wayland at sardemff7.net> wrote:

> On 10/08/2016 14:36, Pekka Paalanen wrote:
> > On Tue, 9 Aug 2016 11:05:49 +0300
> > Pekka Paalanen <ppaalanen at gmail.com> wrote:
> >  
> >> On Mon, 8 Aug 2016 15:59:37 +0200
> >> Quentin Glidic <sardemff7+wayland at sardemff7.net> wrote:
> >>  
> >>> On 08/08/2016 15:45, Pekka Paalanen wrote:  
> >>>> On Tue,  5 Jul 2016 20:41:50 +0200
> >>>> Quentin Glidic <sardemff7+wayland at sardemff7.net> wrote:
> >>>>  
> >>>>> From: Quentin Glidic <sardemff7+git at sardemff7.net>
> >>>>>
> >>>>> Practical example: a client supporting version 2 of wl_output will wait
> >>>>> for the wl_output.done event before starting wl_output-related
> >>>>> operations. However, if the server only supports version 1, no event
> >>>>> will ever come, and it must fallback to use the wl_output.geometry event
> >>>>> alone.
> >>>>> Without this macro, it cannot check for that in a nice way.
> >>>>>
> >>>>> Signed-off-by: Quentin Glidic <sardemff7+git at sardemff7.net>
> >>>>> ---
> >>>>>
> >>>>> I do not have a real world use-case for the request macro on the server-side,
> >>>>> but I guess you could do the same: wait the for a "commit" request if client is
> >>>>> new enough, otherwise use some older request as commit.
> >>>>>
> >>>>> Actually I think there was something like that somewhere, now that I write that,
> >>>>> but I do not remember where exactly.
> >>>>>
> >>>>>
> >>>>>  src/scanner.c | 2 ++
> >>>>>  1 file changed, 2 insertions(+)
> >>>>>
> >>>>> diff --git a/src/scanner.c b/src/scanner.c
> >>>>> index 4708cae..a4c1984 100644
> >>>>> --- a/src/scanner.c
> >>>>> +++ b/src/scanner.c
> >>>>> @@ -1544,10 +1544,12 @@ emit_header(struct protocol *protocol, enum side side)
> >>>>>  			emit_structs(&i->request_list, i, side);
> >>>>>  			emit_opcodes(&i->event_list, i);
> >>>>>  			emit_opcode_versions(&i->event_list, i);
> >>>>> +			emit_opcode_versions(&i->request_list, i);
> >>>>>  			emit_event_wrappers(&i->event_list, i);
> >>>>>  		} else {
> >>>>>  			emit_structs(&i->event_list, i, side);
> >>>>>  			emit_opcodes(&i->request_list, i);
> >>>>> +			emit_opcode_versions(&i->event_list, i);
> >>>>>  			emit_opcode_versions(&i->request_list, i);
> >>>>>  			emit_stubs(&i->request_list, i);
> >>>>>  		}  
> >>>>
> >>>> Hi,
> >>>>
> >>>> I have just one question about this. Users must be able to include both
> >>>> server and client headers in the same compilation unit. Wouldn't this
> >>>> cause the same thing to be #defined in two different headers? More
> >>>> importantly, are we sure it won't cause problems?  
> >>>
> >>> At least with GCC, you can have twice the same #define (same name + same
> >>> value) without issue. I do not know about the C standard take on that
> >>> though.  
> >>
> >> Hi,
> >>
> >> I would need more proof/opinions than just a "it worked for me".
> >>  
> >>> If that would cause problems, it would be because a request and an event
> >>> have the same name, and come from different versions. But if a user must
> >>> be able to include both client and server headers, it is already an issue.  
> >>
> >> I think we can assume that client and server side should use the same
> >> version of the XML files.
> >>
> >> How is it already an issue? Do we already #define something in both
> >> headers?  
> 
> The issue shows up for this kind of protocol:
> <request name="something" since="3" />
> <event name="something" since="2" />
> 
> Currently, with this protocol, including both client and server headers 
> will fail, because one #define will be 3 and the other 2.
> This patch will break even when including one header.
> 
> I guess this kind of protocol is just considered bad design? :-)

Indeed. Are there any known cases of this?

If not, let's go ahead and see if we can get away with it.


Thanks,
pq

> 
> 
> >> At least we already seem to have a test in the Wayland test suite that
> >> includes both client and server protocol headers in the same
> >> compilation unit.
> >>  
> >>> If you really want, I can make server-side define events + prefixed
> >>> requests and the other way around.
> >>>
> >>> server.h:
> >>> #define NAMESPACE_INTERFACE_SOMEEV_SINCE_VERSION 2
> >>> #define NAMESPACE_INTERFACE_REQUEST_SOMEREQ_SINCE_VERSION 3
> >>> client.h:
> >>> #define NAMESPACE_INTERFACE_EVENT_SOMEEV_SINCE_VERSION 2
> >>> #define NAMESPACE_INTERFACE_SOMEREQ_SINCE_VERSION 3  
> >>
> >> I'd like to avoid that naming hassle if possible. I just want to know
> >> if it is possible.  
> >
> > Hi all,
> >
> > after talking to my colleagues and noting that no Microsoft
> > compiler would ever be used to compile this code, my worries have
> > cleared.
> >
> > GCC has this:
> > https://gcc.gnu.org/onlinedocs/cpp/Undefining-and-Redefining-Macros.html
> >
> > I assume Clang would be similar.
> >
> > We can add duplicate #defines just fine. In the unlikely case that it
> > will blow up something, we can fix the generator to emit
> > #ifndef/#define/#endif instead of just #define.
> >
> > How's that for a contingency plan?  
> 
> Good enough for me.
> 
> 
> > The patch is
> > Reviewed-by: Pekka Paalanen <pekka.paalanen at collabora.co.uk>  
> 
> Thanks,
> 

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