[groff] version and revision management

[Bertrand Garrigues]

Hi,

I was starting to prepare the next release and would like to propose a
little change in the version system.  Currently groff's version is set
in 'VERSION' and 'REVISION' files in the top source directory.  When a
new release was planned, the VERSION and/or REVISION files were first
upgraded, then an initial tag was created (for example tag 1.22.3), and
after some testing and fixes the final tag was created with a 'real'
suffix (last tag was: '1.22.3.real').

In order to track more finely the version used when people report an
issue, I propose to use gnulib's script 'git-version-gen' to generate a
unique version.  The other advantage is that installation bugs could be
more easily detected: groff install some data in
/usr/share/groff/<version>, so currently if a commit breaks the
installation of a file this can be unnoticed if the user did not
uninstall its previous version of groff.

'git-version-gen' relies on the command 'git describe' and works roughly
like this:

- From a git repository:

  . if the current commit corresponds to a tag, then the version is
    simply the tag name.

  . Otherwise the version has the following format:
  
      <tag>-<nb_commits>-<commit>

    With:
    -- tag: the most recent tag reachable from the current commit
    -- nb_commits: number of commits between the most recent tag and
      the current commit.
    -- current commit sha1, abbreviated.
    
    For example: 1.22.3.real.434-5aafd

    If there are some local diff the script will also add a 'dirty'
    suffix.
    
  The version is stored in a file '.version'.

- From a tarball, the version is taken from a file '.tarball-version',
  which is generated by the build system.

I've made the necessary changes on a branch 'unique-version'; to test
it:

  git clone https://git.savannah.gnu.org/git/groff.git
  cd groff
  git checkout --track origin/unique-version
  ./bootstrap
  mkdir build
  cd build
  ../configure
  make -j

and to generate the tarball:

  make dist

Note: the full version is propagated in the various executables
generated by the build system (for example 'groff --verrsion' will give
something like "GNU troff (groff) version 1.22.3.real.434-5aafd").
However there is a register '\n[.Y]' that correspond to the revision of
groff; as I can't pass non alphanumeric characters to it (in the above
example the revision would be equal to '3.real.434-5aafd') this register
will be defined as the first alphanumeric digits of the revision.

If no one object to this change then I'll merge it on master.

Regards,

Bertrand Garrigues