difftool: don't assume that default sh is sanecb/mergetool-difftool

git-difftool used to create a command list script containing $( ... )
and explicitly call "sh -c" with this list.

Instead, allow mergetool --tool-help to take a mode parameter and call
mergetool directly to invoke the show_tool_help function. This mode
parameter is intented for use solely by difftool.

Signed-off-by: Charles Bailey <cbailey32@bloomberg.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

2 files changed, 12 insertions, 6 deletions

diff --git a/git-difftool.perl b/git-difftool.perl
index 18ca61e8d0..598fcc23b9 100755
--- a/git-difftool.perl
+++ b/git-difftool.perl
@@ -47,13 +47,9 @@ sub find_worktree
 
 sub print_tool_help
 {
-	my $cmd = 'TOOL_MODE=diff';
-	$cmd .= ' && . "$(git --exec-path)/git-mergetool--lib"';
-	$cmd .= ' && show_tool_help';
-
 	# See the comment at the bottom of file_diff() for the reason behind
 	# using system() followed by exit() instead of exec().
-	my $rc = system('sh', '-c', $cmd);
+	my $rc = system(qw(git mergetool --tool-help=diff));
 	exit($rc | ($rc >> 8));
 }
 
diff --git a/git-mergetool.sh b/git-mergetool.sh
index e969dd0149..d32b663491 100755
--- a/git-mergetool.sh
+++ b/git-mergetool.sh
@@ -320,7 +320,17 @@ guessed_merge_tool=false
 while test $# != 0
 do
 	case "$1" in
-	--tool-help)
+	--tool-help*)
+		case "$#,$1" in
+		1,*=*)
+			TOOL_MODE=$(expr "z$1" : 'z-[^=]*=\(.*\)')
+			;;
+		1,--tool-help)
+			;;
+		*)
+			usage
+			;;
+		esac
 		show_tool_help
 		;;
 	-t|--tool*)