.gitattributes

*.php merge=gumtree

.git|config

[merge "gumtree"]
	name = GumTree merge driver
	driver = .git/gumtree-driver %O %A %B "path-to-gumtree"
	recursive = binary

.git|gumtree-driver

#!/usr/bin/env bash
set -euo pipefail
IFS=$'\n\t'

# https://git-scm.com/docs/gitattributes/2.11.1#_defining_a_custom_merge_driver

# The merge.*.driver variable’s value is used to construct
# a command to run to merge ancestor’s version (%O),
# current version (%A) and the other branches' version (%B).
# These three tokens are replaced with the names of temporary
# files that hold the contents of these versions when the
# command line is built. Additionally, %L will be replaced
# with the conflict marker size (see below).
# The merge driver is expected to leave the result of the
# merge in the file named with %A by overwriting it, and exit
# with zero status if it managed to merge them cleanly,
# or non-zero if there were conflicts.
# The merge driver can learn the pathname in which the merged
# result will be stored via placeholder %P.

if [[ "$#" -ne 4 ]]; then
	echo "Error: Unexpected number of arguments.
Usage:

## .git/config
[merge \"gumtree\"]
	name = GumTree merge driver
	driver = $0 %O %A %B \"path-to-gumtree\"
	recursive = binary

## .gitattributes
*.php merge=gumtree
"
	exit 1
fi

BASE="$1"
OURS="$2"
THEIRS="$3"
GUMTREE="$4"

# GumTree requires valid extension on merged files
cp "$BASE" "$BASE.php"
cp "$OURS" "$OURS.php"
cp "$THEIRS" "$THEIRS.php"

# Clean those temp files regardless of final merge status
function finish {
	rm -f "$BASE.php" "$OURS.php" "$THEIRS.php"
}
trap finish EXIT

# Attemp to merge and save result into "%A" as per Git documentation:
"$GUMTREE" merge "$BASE.php" "$OURS.php" "$THEIRS.php" > "$OURS"

README.md

GumTree merge driver for Git

Setup

1. Download GumTree with Merge Client from https://github.com/Mikulas/gumtree/releases/tag/2.1.0-merge
2. Extract the archive and note the path to gumtree binary
3. In your Git repository, update your .git/config according to the example above. Replace "path-to-gumtree" with the real path.
4. Copy the merge driver into .git/gumtree-driver (also in your git repository)
5. Finally, apply .gitattributes changes to enable the new merge driver.

Usage

After the initial setup, merging is completely transparent. Git will automatically invoke the GumTree merge driver when attempting a merge of two php files.