[PATCH v2 4/4] mergetools/meld: Use '--output' when available

[David Aguilar <davvid@gmail.com>]

meld 1.5.0 and newer allow the output file to be specified
when merging multiple files.  Check whether the meld command
supports '--output' and use it when available.

Signed-off-by: David Aguilar <davvid@gmail.com>
---
 mergetools/meld |   25 ++++++++++++++++++++++++-
 1 files changed, 24 insertions(+), 1 deletions(-)

Changes since v1 with help from Jonathan Nieder:

Use $LOCAL $BASE REMOTE when calling meld.
Avoid shell portability issues by using the return status.
of --output instead of parsing --version.

diff --git a/mergetools/meld b/mergetools/meld
index 73d70ae..eaa115c 100644
--- a/mergetools/meld
+++ b/mergetools/meld
@@ -3,7 +3,30 @@ diff_cmd () {
 }
 
 merge_cmd () {
+	if test -z "${meld_has_output_option:+set}"
+	then
+		check_meld_for_output_version
+	fi
 	touch "$BACKUP"
-	"$merge_tool_path" "$LOCAL" "$MERGED" "$REMOTE"
+	if test "$meld_has_output_option" = true
+	then
+		"$merge_tool_path" --output "$MERGED" \
+			"$LOCAL" "$BASE" "$REMOTE"
+	else
+		"$merge_tool_path" "$LOCAL" "$MERGED" "$REMOTE"
+	fi
 	check_unchanged
 }
+
+# Check whether 'meld --output <file>' is supported
+check_meld_for_output_version () {
+	meld_path="$(git config mergetool.meld.path)"
+	meld_path="${meld_path:-meld}"
+
+	if "$meld_path" --output /dev/null --help >/dev/null 2>&1
+	then
+		meld_has_output_option=true
+	else
+		meld_has_output_option=false
+	fi
+}
-- 
1.7.6.553.g1899