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

[Pekka Paalanen]

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?
> 
> 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?

The patch is
Reviewed-by: Pekka Paalanen <pekka.paalanen at collabora.co.uk>


Thanks,
pq
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