mergetool: Provide an empty file when neededda/maint-mergetool-twoway

Some merge tools cannot cope when $LOCAL, $BASE, or $REMOTE are missing.
$BASE can be missing when two branches independently add the same
filename.

Provide an empty file to make these tools happy.

When a delete/modify conflict occurs, $LOCAL and $REMOTE can also be
missing. We have special case code to handle such case so this change
may not affect that codepath, but try to be consistent and create an
empty file for them anyway.

Reported-by: Jason Wenger <jcwenger@gmail.com>
Signed-off-by: David Aguilar <davvid@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 8 insertions, 4 deletions

diff --git a/git-mergetool.sh b/git-mergetool.sh
index 085e213a12..a9f23f7fcd 100755
--- a/git-mergetool.sh
+++ b/git-mergetool.sh
@@ -181,10 +181,14 @@ stage_submodule () {
 }
 
 checkout_staged_file () {
-    tmpfile=$(expr "$(git checkout-index --temp --stage="$1" "$2")" : '\([^	]*\)	')
+    tmpfile=$(expr \
+	    "$(git checkout-index --temp --stage="$1" "$2" 2>/dev/null)" \
+	    : '\([^	]*\)	')
 
     if test $? -eq 0 -a -n "$tmpfile" ; then
 	mv -- "$(git rev-parse --show-cdup)$tmpfile" "$3"
+    else
+	>"$3"
     fi
 }
 
@@ -224,9 +228,9 @@ merge_file () {
     mv -- "$MERGED" "$BACKUP"
     cp -- "$BACKUP" "$MERGED"
 
-    base_present   && checkout_staged_file 1 "$MERGED" "$BASE"
-    local_present  && checkout_staged_file 2 "$MERGED" "$LOCAL"
-    remote_present && checkout_staged_file 3 "$MERGED" "$REMOTE"
+    checkout_staged_file 1 "$MERGED" "$BASE"
+    checkout_staged_file 2 "$MERGED" "$LOCAL"
+    checkout_staged_file 3 "$MERGED" "$REMOTE"
 
     if test -z "$local_mode" -o -z "$remote_mode"; then
 	echo "Deleted merge conflict for '$MERGED':"