[PATCH 1/2 v3] mergetool--lib: don't call "exit" in setup_tool

[John Keeping <john@keeping.me.uk>]

This will make it easier to use setup_tool in places where we expect
that the selected tool will not support the current mode.

We need to introduce a new return code for setup_tool to differentiate
between the case of "the selected tool is invalid" and "the selected
tool is not a built-in" since we must call setup_tool when a custom
'merge.<tool>.path' is configured for a built-in tool but avoid failing
when the configured tool is not a built-in.

Signed-off-by: John Keeping <john@keeping.me.uk>
---
> On Fri, Jan 25, 2013 at 04:24:03PM -0800, Junio C Hamano wrote:
> > Applying this one on top of 1/7 thru 5/7 and 7/7 seems to break
> > t7610 rather badly.
> 
> Sorry about that.  The 'setup_tool' function should really be called
> 'setup_builtin_tool' - it isn't necessary when a custom mergetool is
> configured and will return 1 when called with an argument that isn't a
> builtin tool from $GIT_EXEC_PATH/mergetools.
> 
> The change is the second hunk below which now wraps the call to
> setup_tool in an if block as well as adding the "|| return".

Now that I've run the entire test suite, that still wasn't correct since
it did not correctly handle the case where the user overrides the path
for one of the built-in mergetools.

 git-mergetool--lib.sh | 23 ++++++++++++++++++++---
 1 file changed, 20 insertions(+), 3 deletions(-)

diff --git a/git-mergetool--lib.sh b/git-mergetool--lib.sh
index 4c1e129..dd4f088 100644
--- a/git-mergetool--lib.sh
+++ b/git-mergetool--lib.sh
@@ -58,7 +58,11 @@ setup_tool () {
 	. "$mergetools/defaults"
 	if ! test -f "$mergetools/$tool"
 	then
-		return 1
+		# Use a special return code for this case since we want to
+		# source "defaults" even when an explicit tool path is
+		# configured since the user can use that to override the
+		# default path in the scriptlet.
+		return 2
 	fi
 
 	# Load the redefined functions
@@ -67,11 +71,11 @@ setup_tool () {
 	if merge_mode && ! can_merge
 	then
 		echo "error: '$tool' can not be used to resolve merges" >&2
-		exit 1
+		return 1
 	elif diff_mode && ! can_diff
 	then
 		echo "error: '$tool' can only be used to resolve merges" >&2
-		exit 1
+		return 1
 	fi
 	return 0
 }
@@ -101,6 +105,19 @@ run_merge_tool () {
 
 	# Bring tool-specific functions into scope
 	setup_tool "$1"
+	exitcode=$?
+	case $exitcode in
+	0)
+		:
+		;;
+	2)
+		# The configured tool is not a built-in tool.
+		test -n "$merge_tool_path" || return 1
+		;;
+	*)
+		return $exitcode
+		;;
+	esac
 
 	if merge_mode
 	then
-- 
1.8.1