Git merge driver for PO files

git-merge-po.sh

#!/bin/sh
#
# *******************************************
# WARNING: this does *not* handle 3-way merges properly.
# Anything modified on the local branch since the common base will get ignored.
#
# FOR ANYONE LANDING HERE:
# This script is now updated as part of the git-whistles gem.
# https://github.com/mezis/git-whistles
# *******************************************
#
# Custom Git merge driver - merges PO files using msgcat(1)
#
# - Install gettext
#
# - Place this script in your PATH
# 
# - Add this to your .git/config :
#
#   [merge "pofile"]
#     name = Gettext merge driver
#     driver = git merge-po %O %A %B
# 
# - Add this to .gitattributes :
# 
#   *.po   merge=pofile
#   *.pot  merge=pofile
#
# - When merging branches, conflicts in PO files will be maked with "#-#-#-#"
# 
O=$1
A=$2
B=$3

# Extract the PO header from the current branch (top of file until first empty line)
header=$(mktemp /tmp/merge-po.XXXX)
sed -e '/^$/q' < $A > $header

# Merge files, then repair header
temp=$(mktemp /tmp/merge-po.XXXX)
msgcat -o $temp $A $B
msgcat --use-first -o $A $header $temp

# Clean up
rm $header $temp

# Check for conflicts
conflicts=$(grep -c "#-#" $A)
test $conflicts -gt 0 && exit 1
exit 0

What is a po files?

dbolser-ebi: I don't know how you hit this page without knowing what is a PO file.

A .po file is used as a source for GNU gettext tools. It's usually converted to .mo file format with command msgfmt which is also part of gettext. A .po file looks a lot like a normal text file but it really is a database format for gettext localizations. And if you allow normal git merge driver to do the merge as if the file was a normal text file, you'll end up with a corrupted .po file. The gettext does include a command called msgmerge but despite its name, it is not suitable for merging different versions of localizations.

There was a pull request to add msg3way to gettext around 4 years ago (http://lists.gnu.org/archive/html/bug-gnu-utils/2010-11/msg00051.html) but it never got any traction.

@mikkorantalainen: I found this page by searching on how to build a custom git merge strategy. This is one of the only examples that shows how you can build one and integrate it into your project.

For anyone still interested, git-whistles is getting a proper 3-way PO merger. Doesn't rely on Perl and string wrangling line the SO suggestions pointed to by @mikkorantalainen (which were a great source of inspiration).

mezis/git-whistles#39

Here's a link to 3-way merge for PO files that I currently use: https://stackoverflow.com/a/68799310/334451
It has some ideas from my older driver and some ideas that @mezis used and I partially re-wrote it to run on multiple CPU cores as much as possible. I've been using it for a couple of years without any invalid merges so I consider that the best solution until gettext includes proper 3-way merge one day.

@mikkorantalainen: I found this page by searching on how to build a custom git merge strategy. This is one of the only examples that shows how you can build one and integrate it into your project.

me too