font-patcher: Use git version tag for font version

[why]
When changes are made to the font-patcher and fonts are patched with
that version we can not see which patcher has been used in the fonts
afterwards.

Would be good to have the usual version-patchversion number in the fonts
in these cases (i.e. `v2.3.3-7` for 7 commits after `2.3.3`).

I did this manually before, but it is always a hassle.

[how]
If the font-patcher is run directly from a git repo and git is installed
we try to get the latest tag version including patch number.

If and only if that is successful and that version is 'newer' than the
version encoded in the font-patcher script the git version is trusted
more.

Signed-off-by: Fini Jastrow <[email protected]>

font-patcher

@@ -1588,6 +1588,34 @@ def check_fontforge_min_version():
         sys.stderr.write("{}: Please use at least version: {}\n".format(projectName, minimumVersion))
         sys.exit(1)
 
+def check_version_with_git(version):
+    """ Upgraded the version to the current git tag version (starting with 'v') """
+    git = subprocess.run("git describe --tags",
+            cwd=os.path.dirname(__file__),
+            shell=True,
+            stdout=subprocess.PIPE, stderr=subprocess.DEVNULL
+        ).stdout.decode('utf-8')
+    if len(git) == 0:
+        return False
+    tag = git.strip()
+    if len(tag) == 0 or not tag.startswith('v'):
+        return False
+    tag = tag[1:]
+    r = re.search('(.*?)(-[0-9]+)-g[0-9a-fA-F]+$', tag)
+    if r:
+        tag = r.group(1)
+        patchlevel = r.group(2)
+    else:
+        patchlevel = ""
+    # Inspired by Phaxmohdem's versiontuple https://stackoverflow.com/a/28568003
+
+    versiontuple = lambda v: tuple( p.zfill(8) for p in v.split(".") )
+    if versiontuple(tag) > versiontuple(version):
+        return tag + patchlevel
+    if versiontuple(tag) == versiontuple(version) and len(patchlevel) > 0:
+        return tag + patchlevel
+    return False
+
 def setup_arguments():
     parser = argparse.ArgumentParser(
         description=(
@@ -1716,7 +1744,12 @@ def setup_arguments():
 
 
 def main():
-    print("{} Patcher v{} ({}) executing".format(projectName, version, script_version))
+    global version
+    git_version = check_version_with_git(version)
+    print("{} Patcher v{} ({}) (ff {}) executing".format(
+        projectName, git_version if git_version else version, script_version, fontforge.version()))
+    if git_version:
+        version = git_version
     check_fontforge_min_version()
     args = setup_arguments()
     patcher = font_patcher(args)