[Spice-devel] [PATCH] Fix build when builddir != srcdir

[Frediano Ziglio]

> On Wed, 2016-11-16 at 11:18 -0500, Frediano Ziglio wrote:
> > > 
> > > 
> > > On Wed, 2016-11-16 at 06:20 -0500, Frediano Ziglio wrote:
> > > > 
> > > > > 
> > > > > 
> > > > > 
> > > > > 
> > > > > Acked-by: Christophe Fergeau <cfergeau at redhat.com>
> > > > > 
> > > > > On Tue, Nov 15, 2016 at 12:13:21PM -0600, Jonathon Jongsma
> > > > > wrote:
> > > > > > 
> > > > > > 
> > > > > > The following build error occurs when building outside of the
> > > > > > source
> > > > > > directory:
> > > > > > 
> > > > > > glib-mkenums --template spice-server-enums.tmpl.c
> > > > > > ../../server/spice-server.h > spice-server-enums.c
> > > > > > Can't open spice-server-enums.tmpl.c: No such file or
> > > > > > directory
> > > > > > Makefile:1111: recipe for target 'spice-server-enums.c'
> > > > > > failed
> > > > > > 
> > > > > > GNU Make does some magic to know that the spice-server-
> > > > > > enums.tmpl.c file
> > > > 
> > > > It's a combination of automake and VPATH (which is currently
> > > > quite
> > > > standard
> > > > so it's more a automake setting).
> > > > 
> > > > > 
> > > > > 
> > > > > > 
> > > > > > 
> > > > > > listed in the prerequisites for the rule is located in the
> > > > > > srcdir. But
> > > > > > when we use the bare filename in the rule definition, it
> > > > > > assumes
> > > > > > that it is
> > > > > > in the builddir. If there was an automatic variable that we
> > > > > > could
> > > > > > use
> > > > > > (like $< that we already use for the first prerequisite), the
> > > > > > srdir
> > > > 
> > > > From this part of the comment seems there is no way to extract
> > > > the
> > > > second prerequisite. In GNU make you can use $(word 2,$^) if you
> > > > want to do this without using some hacks.
> > > > Also is not that make assumes that is in builddir is that make
> > > > does not parse much the rules definitions as doing so would cause
> > > > problems. Is not defined for instance that you want to use
> > > > spice-server-enums.tmpl.c as a filename so should try to find
> > > > the file. As far as make is concern it's just a string. The
> > > > parsing
> > > > of rule body is limited to $ (which can be quoted) and line
> > > > joiningm
> > > > beside that lines are passed verbatim to the shell (which can be
> > > > changed).
> > > 
> > > True, we could use a make function, but I'd still prefer to just
> > > prepend
> > > $(srcdir) explicitly. I think it's more straightforward.
> > > 
> > > > 
> > > > 
> > > > > 
> > > > > 
> > > > > > 
> > > > > > 
> > > > > > would be automatically prepended to the filename, but there's
> > > > > > nothing we
> > > > > > can use for the second prerequisite. So we need to explicitly
> > > > > > specify
> > > > > > the location of the input template file.
> > > > 
> > > > I would remove this part.
> > > 
> > > 
> > > How about this?
> > > 
> > >     Make/Automake uses VPATH to determine that the spice-server-
> > > enums.tmpl.c
> > >     file listed in the prerequisites for the rule is located in the
> > > srcdir.
> > >     When we use an automatic variable (e.g. $<), the srcdir path
> > > gets
> > >     automatically prepended to the filename. But when we use the
> > > filename
> > >     directly within the rule definition, this won't happen. So we
> > > need to
> > >     explicitly specify that the input template file is located in
> > > srcdir.
> > > 
> > > Jonathon
> > > 
> > 
> > Not exactly. Specifically
> > 
> > "When we use an automatic variable (e.g. $<), the srcdir path gets
> >  automatically prepended to the filename."
> > 
> > It's not that $< is expanded is that when the prerequisite
> > are evaluated (which is distinct from where are parsed) make try to
> > resolve
> > the files and potentially expand them if needed (or create them, but
> > this is OT). So when the rule is called the prerequisites are already
> > resolved
> > with proper paths. When $< is used in this case the first
> > prerequisite is
> > picked up (kind of $(word 1,$^)) which is already resolved.
> > 
> > Frediano
> 
> 
> I thought that's basically what I said, although perhaps I didn't use
> precise language. How about:
> 
> Make/Automake uses VPATH to determine that the spice-server-
> enums.tmpl.c file listed in the prerequisites for the rule is located
> in the srcdir. When we use an automatic variable (e.g. $<), the full
> path to the resolved file is used. But when we use the literal filename
> directly within the rule definition, this won't happen. So we need to
> explicitly specify that the input template file is located in srcdir.
> 

Yes, today I'm move picky than usual.

Acked-by: Frediano Ziglio <fziglio at redhat.com>

Frediano