git-meld

#!/bin/bash

tmpdir=/tmp/.git-meld
lock="$tmpdir"/.lock
lock_timeout=30
link=meld-git
umask 077


if [[ "$(basename "$0")" = git-meld ]]
then
	mkdir -p "$tmpdir"

	exec 4>>"$lock"
	flock -w "$lock_timeout" -E 43 4
	[[ $? -eq 43 ]] && {
		echo >&2 "Failed to acquire lock for git-meld: $lock"
		# notify-send -i meld\
		# 	'Failed to acquire lock for git-meld'\
		# 	"Lock path: ${lock}, timeout: ${lock_timeout}s"
		exit 1
	}
	:>"$lock" # flush old contents

	GIT_EXTERNAL_DIFF=$link GIT_PAGER= git diff "$@" || exit

	lock_meld="$lock".$$
	readarray -t files <"$lock"
	cp "$lock" "$lock_meld"

	exec 5>>"$lock_meld"
	flock -n 5 || exit 2

	src= meld_args=()
	for p in "${files[@]}"; do
		[[ -z "$src" ]] && { src=$p; continue; }
		meld_args+=( --diff "$src" "$p" ) src=
	done
	[[ -n "$src" ]] && {
		echo >&2 "Uneven number of diff-files (leftover: $src)"
		exit 1
	}

	# Do cleanup for old diffs
	for p in "$lock".*; do
		pid=${p##*.}
		exec 6>>"$p"
		flock -n 6 || continue # meld is still alive
		readarray -t files <"$p"
		rm -f "$p"
		for p in "${files[@]}"; do
			[[ "$p" =~ ^"$tmpdir"/ ]] && { rm -f "$p"; continue; }
			echo >&2 "BUG: tried to remove non-tmpdir ($tmpdir) file - $p (left from pid: $pid)"
			exit 3
		done
	done

	[[ "${#meld_args[@]}" -eq 0 ]] && exit 0
	exec 1>/dev/null 2>/dev/null # meld is very noisy ;(
	exec meld "${meld_args[@]}"

else
	# Gather files into tmpdir, pushing names to lockfile
	# Expected to be called multiple times by git-diff
	[[ ! ( -f "$2" || "$2" = /dev/null ) || ! ( -f "$5" || "$5" = /dev/null ) || "$3" = "$6" ]] && {
		echo >&2 "Skipping diff for: $2 ($3) $5 ($6)"
		exit 0
	}

	# old
	dst="${tmpdir}/$$.$3.$(basename "$1")"
	cp "$2" "$dst" || exit
	echo "$dst" >>"$lock"

	# new
	dst="${tmpdir}/$$.$6.$(basename "$1")"
	cp "$5" "$dst" || exit
	echo "$dst" >>"$lock"

fi