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Subject: Re: [Boost-build] How to specify build order so I can use svnversion?
From: Steve Soule (sts11dbxr_at_[hidden])
Date: 2010-04-24 13:23:53

On 04/23/2010 06:10 PM, Steve Soule wrote:
> I'm working on a project where the svn version number of my source code
> needs to be embedded in the executable (so that it can be viewed by the
> user). The "svnversion" command produces this svn version number. I
> need to put the output of svnversion in a source file that is compiled
> into the executable.
> I need to figure out how to make Boost Build do this correctly. The svn
> version number doesn't change very often--perhaps one in one hundred
> builds. So most of the time, the Jam code for including the svn version
> should not result in rebuilding anything.
> I've spent all day trying to figure this out. The best I've come up
> with so far is the following Jamroot.jam (greatly simplified):
> exe vprogram : [ glob src/*.cpp ] ;
> import notfile ;
> notfile write_svn_version : @write_svn_version_action ;
> actions write_svn_version_action
> {
> echo '"'`svnversion`'"' >svn_version_tmp.hpp
> if diff -N svn_version_tmp.hpp src/svn_version.hpp >/dev/null; then
> rm svn_version_tmp.hpp
> else
> mv svn_version_tmp.hpp src/svn_version.hpp
> fi
> }
> Effectively, this makes bjam check the output of svnversion; if the
> output has changed, it replaces the file src/svn_version.hpp with the
> new version.
> This works fine except for one problem: the write_svn_version target is
> built after the vprogram target, so the executable is built using the
> svn version from the last build rather than this build. All I have to
> do is remember to run bjam twice, and the result is correct, and
> practically no unnecessary rebuilding takes place.
> However, I might forget to execute bjam twice, so I would really like to
> know how to make bjam build the write_svn_version target before the
> vprogram target.
> I've spent all day working on this, and I've tried dozens of different
> things. Most of the things I've tried have resulted in creating a
> dependency between vprogram and write_svn_version. Because the
> write_svn_version target is always out-of-date, if any target depends on
> it, that target is always rebuilt. In many of my attempts, every source
> file in vprogram is rebuilt, even though nothing needs to be. I don't
> think it makes sense for vprogram to depend on write_svn_version.
> It seems like the solution should be simple. There should be an easy
> way to tell Boost Build to build write_svn_version before vprogram
> (without creating a dependency). But I haven't been able to find
> anything in the documentation. I'm stumped.
> What is the solution?

Well, apparently all I had to do was sleep on it, because I had no
trouble figuring it out this morning. Sorry for wasting everyone's
time. In case anyone's interested, here's my solution (greatly simplified):

cur_ver = [ SHELL "echo '\"'`svnversion`'\"'" ] ;
old_ver = [ SHELL "cat src/svn_version.hpp" ] ;
if $(cur_ver) != $(old_ver)
    import notfile ;
    notfile write_svn_version : @write_svn_version_action ;
    actions write_svn_version_action
        echo '"'`svnversion`'"' >src/svn_version.hpp
    alias write_svn_version ;

obj src/svn_version : src/svn_version.cpp : <dependency>write_svn_version ;

exe vprogram : [ glob src/*.cpp : src/svn_version.cpp ] ;

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