On 12/22/2012 09:07 AM, Jef Driesen wrote: > On 22-12-12 16:18, Eric Blake wrote: >> [adding autoconf, as this question technically is independent of >> automake] >> > What I want to accomplish is as follows. I have a dc_version() function > in my library which returns the version number. The main part of the > version number is generated directly from configure.ac (with AC_SUBST > and a version.h.in file). But I also generate a revision.h file at build > time containing the git SHA1. So far no problem. But now I'm trying to > append this git revision info for non-release builds (e.g. > dc_version_suffix not empty).
You may be interested in seeing how GNU Coreutils approaches this. It uses a tool git-version-gen from gnulib, as well as some hooks into configure.ac and Makefile.am, so that if you are building from coreutils.git, then the git version is injected as a suffix into the generated version string via a file version.[ch], and if you are building from a tarball, then the information is hard-coded and there is no suffix. By sticking the version information in a separate .c file, it becomes merely a matter of linking to the new .o file (rather than recompiling the world) when the version number changes. > So my version.c file contains roughly this: > > #ifdef HAVE_CONFIG_H > #include "config.h" > #endif Within a single project, you should know whether you are using config.h; being conditional only matters for libraries like libtool that are designed to work even without autoconf. That is, these days, most people _don't_ need #ifdef HAVE_CONFIG_H, but can blindly assume that it is in use. > > #include <libdivecomputer/version.h> /* Defines the DC_VERSION macro. */ > > #ifdef USE_REVISION > #include "revision.h"/* Defines the DC_VERSION_REVISION macro. */ > #endif Makes sense. > So I wanted to have this USE_REVISION macro somehow end up in the > config.h header, such that the above code would work. > > The m4_ifset based test does that, but if the dc_version_suffix is > empty, the USE_REVISION macro is not present in the config.h file at > all. Usually when you define any sort of tests (e.g. AC_CHECK_*), then > the corresponding macros always ends up in the config.h file, but > uncommented when not available. Like this: > > /* Use the revision number. */ > /* #undef USE_REVISION */ Ah, so you want the template to be visible to autoheader, even when the template is not in use from a tarball. > > When using an AS_IF based test, that's the case too. So that's why I > thought the m4_ifset test was not the right tool. Yeah, m4_ifset hides the entire AC_DEFINE from view of any other tool, like autoheader, that scans for m4 calls. If you want the template to appear unconditionally, but only be defined when needed, you might try: if m4_ifset([dc_version_suffix], [:], [false]); then AC_DEFINE([USE_REVISION], [1], [Use the revision number.]) fi which then makes the AC_DEFINE() unconditionally expanded at m4 time (so autoheader will list the template), but the shell decision on whether to do anything is now minimized. -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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