[PATCH v2] mergetool: support setting path to tool as config var mergetool.<tool>.path

[Steffen Prohaska <prohaska@zib.de>]

This commit adds a mechanism to provide absolute paths to the
external programs called by 'git mergetool'. A path can be
specified in the configuation variable mergetool.<tool>.path.
The configuration variable is similar to how we name branches
and remotes. It is extensible if we need to specify more details
about a tool.

The mechanism added by this patch is orthogonal to the existing
merge.tool configuration variable:
1) merge.tool selects a tool from a list of known programs for which
command line arguments and the mechanism for returning merge results is know.
2) mergetool.<tool>.path provides details on how to locate the selected
tool in the filesystem. Paths for several tools can be configured simultaneously.

The mechanism is especially useful on Windows, where external
programs are unlikely to be in PATH.

Signed-off-by: Steffen Prohaska <prohaska@zib.de>
---
 Documentation/git-mergetool.txt |    6 ++
 git-mergetool.sh                |   97 +++++++++++++++++++++-----------------
 2 files changed, 60 insertions(+), 43 deletions(-)

This updated patch is based on the the comments and suggestions by
Theodor, Frank, and Johannes.

    Steffen

diff --git a/Documentation/git-mergetool.txt b/Documentation/git-mergetool.txt
index 6c32c6d..17a33e7 100644
--- a/Documentation/git-mergetool.txt
+++ b/Documentation/git-mergetool.txt
@@ -31,6 +31,12 @@ If a merge resolution program is not specified, 'git mergetool'
 will use the configuration variable merge.tool.  If the
 configuration variable merge.tool is not set, 'git mergetool'
 will pick a suitable default.
++
+You can explicitly provide a full path to the tool by setting the
+configuration variable mergetool.<tool>.path. For example, you
+can configure the absolute path to kdiff3 by setting
+mergetool.kdiff3.path. Otherise, 'git mergetool' assumes the tool
+is available in PATH.
 
 Author
 ------
diff --git a/git-mergetool.sh b/git-mergetool.sh
index 9f4f313..1e4583f 100755
--- a/git-mergetool.sh
+++ b/git-mergetool.sh
@@ -192,10 +192,10 @@ merge_file () {
     case "$merge_tool" in
 	kdiff3)
 	    if base_present ; then
-		(kdiff3 --auto --L1 "$path (Base)" --L2 "$path (Local)" --L3 "$path (Remote)" \
+		("$merge_tool_path" --auto --L1 "$path (Base)" --L2 "$path (Local)" --L3 "$path (Remote)" \
 		    -o "$path" -- "$BASE" "$LOCAL" "$REMOTE" > /dev/null 2>&1)
 	    else
-		(kdiff3 --auto --L1 "$path (Local)" --L2 "$path (Remote)" \
+		("$merge_tool_path" --auto --L1 "$path (Local)" --L2 "$path (Remote)" \
 		    -o "$path" -- "$LOCAL" "$REMOTE" > /dev/null 2>&1)
 	    fi
 	    status=$?
@@ -203,35 +203,35 @@ merge_file () {
 	    ;;
 	tkdiff)
 	    if base_present ; then
-		tkdiff -a "$BASE" -o "$path" -- "$LOCAL" "$REMOTE"
+		"$merge_tool_path" -a "$BASE" -o "$path" -- "$LOCAL" "$REMOTE"
 	    else
-		tkdiff -o "$path" -- "$LOCAL" "$REMOTE"
+		"$merge_tool_path" -o "$path" -- "$LOCAL" "$REMOTE"
 	    fi
 	    status=$?
 	    save_backup
 	    ;;
 	meld|vimdiff)
 	    touch "$BACKUP"
-	    $merge_tool -- "$LOCAL" "$path" "$REMOTE"
+	    "$merge_tool_path" -- "$LOCAL" "$path" "$REMOTE"
 	    check_unchanged
 	    save_backup
 	    ;;
 	gvimdiff)
 		touch "$BACKUP"
-		gvimdiff -f -- "$LOCAL" "$path" "$REMOTE"
+		"$merge_tool_path" -f -- "$LOCAL" "$path" "$REMOTE"
 		check_unchanged
 		save_backup
 		;;
 	xxdiff)
 	    touch "$BACKUP"
 	    if base_present ; then
-		xxdiff -X --show-merged-pane \
+		"$merge_tool_path" -X --show-merged-pane \
 		    -R 'Accel.SaveAsMerged: "Ctrl-S"' \
 		    -R 'Accel.Search: "Ctrl+F"' \
 		    -R 'Accel.SearchForward: "Ctrl-G"' \
 		    --merged-file "$path" -- "$LOCAL" "$BASE" "$REMOTE"
 	    else
-		xxdiff -X --show-merged-pane \
+		"$merge_tool_path" -X --show-merged-pane \
 		    -R 'Accel.SaveAsMerged: "Ctrl-S"' \
 		    -R 'Accel.Search: "Ctrl+F"' \
 		    -R 'Accel.SearchForward: "Ctrl-G"' \
@@ -243,18 +243,18 @@ merge_file () {
 	opendiff)
 	    touch "$BACKUP"
 	    if base_present; then
-		opendiff "$LOCAL" "$REMOTE" -ancestor "$BASE" -merge "$path" | cat
+		"$merge_tool_path" "$LOCAL" "$REMOTE" -ancestor "$BASE" -merge "$path" | cat
 	    else
-		opendiff "$LOCAL" "$REMOTE" -merge "$path" | cat
+		"$merge_tool_path" "$LOCAL" "$REMOTE" -merge "$path" | cat
 	    fi
 	    check_unchanged
 	    save_backup
 	    ;;
 	emerge)
 	    if base_present ; then
-		emacs -f emerge-files-with-ancestor-command "$LOCAL" "$REMOTE" "$BASE" "$(basename "$path")"
+		"$merge_tool_path" -f emerge-files-with-ancestor-command "$LOCAL" "$REMOTE" "$BASE" "$(basename "$path")"
 	    else
-		emacs -f emerge-files-command "$LOCAL" "$REMOTE" "$(basename "$path")"
+		"$merge_tool_path" -f emerge-files-command "$LOCAL" "$REMOTE" "$(basename "$path")"
 	    fi
 	    status=$?
 	    save_backup
@@ -297,17 +297,38 @@ do
     shift
 done
 
+valid_tool() {
+	case "$1" in
+		kdiff3 | tkdiff | xxdiff | meld | opendiff | emerge | vimdiff | gvimdiff)
+			;; # happy
+		*)
+			return 1
+			;;
+	esac
+}
+
+init_merge_tool_path() {
+	merge_tool_path=`git config mergetool.$1.path`
+	if test -z "$merge_tool_path" ; then
+		case "$merge_tool" in
+			emerge)
+				merge_tool_path=emacs
+				;;
+			*)
+				merge_tool_path=$merge_tool
+				;;
+		esac
+	fi
+}
+
+
 if test -z "$merge_tool"; then
     merge_tool=`git config merge.tool`
-    case "$merge_tool" in
-	kdiff3 | tkdiff | xxdiff | meld | opendiff | emerge | vimdiff | gvimdiff | "")
-	    ;; # happy
-	*)
+    test -n "$merge_tool" || valid_tool "$merge_tool" || {
 	    echo >&2 "git config option merge.tool set to unknown tool: $merge_tool"
 	    echo >&2 "Resetting to default..."
 	    unset merge_tool
-	    ;;
-    esac
+    }
 fi
 
 if test -z "$merge_tool" ; then
@@ -329,40 +350,30 @@ if test -z "$merge_tool" ; then
     merge_tool_candidates="$merge_tool_candidates opendiff emerge vimdiff"
     echo "merge tool candidates: $merge_tool_candidates"
     for i in $merge_tool_candidates; do
-        if test $i = emerge ; then
-            cmd=emacs
-        else
-            cmd=$i
-        fi
-        if type $cmd > /dev/null 2>&1; then
+        init_merge_tool_path $i
+        if type "$merge_tool_path" > /dev/null 2>&1; then
             merge_tool=$i
             break
         fi
     done
     if test -z "$merge_tool" ; then
-	echo "No available merge resolution programs available."
+	echo "No known merge resolution program available."
 	exit 1
     fi
+else
+    valid_tool "$merge_tool" || {
+        echo >&2 "Unknown merge_tool $merge_tool"
+        exit 1
+    }
+
+    init_merge_tool_path "$merge_tool"
+
+    if ! type "$merge_tool_path" > /dev/null 2>&1; then
+        echo "The merge tool $merge_tool is not available as '$merge_tool_path'"
+        exit 1
+    fi
 fi
 
-case "$merge_tool" in
-    kdiff3|tkdiff|meld|xxdiff|vimdiff|gvimdiff|opendiff)
-	if ! type "$merge_tool" > /dev/null 2>&1; then
-	    echo "The merge tool $merge_tool is not available"
-	    exit 1
-	fi
-	;;
-    emerge)
-	if ! type "emacs" > /dev/null 2>&1; then
-	    echo "Emacs is not available"
-	    exit 1
-	fi
-	;;
-    *)
-	echo "Unknown merge tool: $merge_tool"
-	exit 1
-	;;
-esac
 
 if test $# -eq 0 ; then
 	files=`git ls-files -u | sed -e 's/^[^	]*	//' | sort -u`
-- 
1.5.3.3.127.g40d17