[PATCH wayland 3/3] scanner: check for wayland-scanner.pc before using variables

[Kristian Høgsberg]

On Wed, Aug 07, 2013 at 04:33:20PM +1000, Peter Hutterer wrote:
> On Wed, Aug 07, 2013 at 07:46:43AM +0200, Daiki Ueno wrote:
> > Hi,
> > 
> > Peter Hutterer <peter.hutterer at who-t.net> writes:
> > 
> > >  AC_DEFUN([WAYLAND_SCANNER_RULES], [
> > >      PKG_PROG_PKG_CONFIG
> > >  
> > > +    PKG_CHECK_MODULES([WAYLAND_SCANNER], [wayland-scanner])
> > > +
> > 
> > With this change, configure will abort if wayland-scanner.pc is not
> > found.  However, the current WAYLAND_SCANNER_RULES cannot be invoked
> > conditionally, because the make rules are expanded using AC_SUBST_FILE:
> > 
> >     wayland_scanner_rules=`$PKG_CONFIG --variable=pkgdatadir wayland-scanner`/wayland-scanner.mk
> >     AC_SUBST_FILE([wayland_scanner_rules])
> > 
> > and in Makefile.am:
> > 
> >     @wayland_scanner_rules@
> > 
> > which will be left unexpanded and cause a syntax error if
> > WAYLAND_SCANNER_RULES is not invoked.  Note that Automake conditionals
> > don't work for the multiline substitution variables.
> > 
> > Perhaps an idea is changing the substitution to:
> > 
> >     wayland_scanner_rules=`$PKG_CONFIG --variable=pkgdatadir wayland-scanner`/wayland-scanner.mk
> >     AC_SUBST_FILE([wayland_scanner_rules])
> >     AC_SUBST([wayland_scanner_makefile], [$wayland_scanner_rules])
> > 
> > and in Makefile.am, include the rule instead of embedding:
> > 
> >     -include $(wayland_scanner_makefile)
> > 
> > By the way,
> > 
> > > If wayland-scanner.pc can't be found the variables end up being set
> > > irrespectively, leaving the user with odd compiler errors about missing
> > > headers, etc.
> > 
> > Did you actually get any errors?  I didn't get any, when compiling the
> > Wayland support for IBus, without Wayland installation.
> 
> yep, I don't go searching for these things ;)
> happened when building weston, and the problem in my case was that
> PKG_CONFIG_PATH pointed to $prefix/lib/pkgconfig but not
> $prefix/share/pkgconfig. which is a setup problem, but we shouldn't trust
> that a package is there.
> 
> The real problem is that the error message is non-intuitive:
> make[2]: *** No rule to make target `screenshooter-server-protocol.h',
> needed by `all'.  Stop.
> 
> I guess the easiest alternative here would be to have a fixed dependency on
> wayland-scanner in weston.

I'm open to dropping this whole mess and just copy and paste the three
makefile rules around.  Trying to do this "right" through autotool has
been much more trouble than it's worth.

Kristian