mergetools/diffmerge: support DiffMerge as a git mergetool

DiffMerge is a non-free (but gratis) tool that supports OS X, Windows and Linux.

    See http://www.sourcegear.com/diffmerge/

DiffMerge includes a script `/usr/bin/diffmerge` that can be used to launch the
graphical compare tool.

This change adds mergetool support for DiffMerge and adds 'diffmerge' as an
option to the mergetool help.
Signed-off-by: NStefan Saasen <ssaasen@atlassian.com>
Acked-by: NDavid Aguilar <davvid@gmail.com>
Signed-off-by: NJonathan Nieder <jrnieder@gmail.com>

contrib/completion/git-completion.bash

@@ -1188,7 +1188,7 @@ _git_diff ()
 	__git_complete_revlist_file
 }
 
-__git_mergetools_common="diffuse ecmerge emerge kdiff3 meld opendiff
+__git_mergetools_common="diffuse diffmerge ecmerge emerge kdiff3 meld opendiff
 			tkdiff vimdiff gvimdiff xxdiff araxis p4merge bc3 codecompare
 "
 

git-mergetool--lib.sh

@@ -250,7 +250,8 @@ list_merge_tool_candidates () {
 		else
 			tools="opendiff kdiff3 tkdiff xxdiff meld $tools"
 		fi
-		tools="$tools gvimdiff diffuse ecmerge p4merge araxis bc3 codecompare"
+		tools="$tools gvimdiff diffuse diffmerge ecmerge"
+		tools="$tools p4merge araxis bc3 codecompare"
 	fi
 	case "${VISUAL:-$EDITOR}" in
 	*vim*)

mergetools/diffmerge

+diff_cmd () {
+	"$merge_tool_path" "$LOCAL" "$REMOTE" >/dev/null 2>&1
+}
+
+merge_cmd () {
+	if $base_present
+	then
+		"$merge_tool_path" --merge --result="$MERGED" \
+			"$LOCAL" "$BASE" "$REMOTE"
+	else
+		"$merge_tool_path" --merge \
+			--result="$MERGED" "$LOCAL" "$REMOTE"
+	fi
+	status=$?
+}