mergetools/p4merge: Honor $TMPDIR for the /dev/null placeholder

Use $TMPDIR when creating the /dev/null placeholder for p4merge.
This prevents users from finding a seemingly random untracked file
in their worktree.

This is different than what mergetool does with $LOCAL and
$REMOTE because those files exist to aid users when resolving
merges.  p4merge's /dev/null placeholder is not helpful in that
situation so it is sensible to keep it out of the worktree.

Reported-by: Jeremy Morton <admin@game-point.net>
Signed-off-by: David Aguilar <davvid@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/mergetools/p4merge b/mergetools/p4merge
index 295361a8aa7d075bbb9fdb8173858e37f9a43211..52f7c8f70578929432becdd58a7fb423398f8de8 100644 (file)
--- a/mergetools/p4merge
+++ b/mergetools/p4merge
@@ -1,29 +1,21 @@
 diff_cmd () {
+       empty_file=
+
        # p4merge does not like /dev/null
-       rm_local=
-       rm_remote=
        if test "/dev/null" = "$LOCAL"
        then
-               LOCAL="./p4merge-dev-null.LOCAL.$$"
-               >"$LOCAL"
-               rm_local=true
+               LOCAL="$(create_empty_file)"
        fi
        if test "/dev/null" = "$REMOTE"
        then
-               REMOTE="./p4merge-dev-null.REMOTE.$$"
-               >"$REMOTE"
-               rm_remote=true
+               REMOTE="$(create_empty_file)"
        fi
 
        "$merge_tool_path" "$LOCAL" "$REMOTE"
 
-       if test -n "$rm_local"
-       then
-               rm -f "$LOCAL"
-       fi
-       if test -n "$rm_remote"
+       if test -n "$empty_file"
        then
-               rm -f "$REMOTE"
+               rm -f "$empty_file"
        fi
 }
 
@@ -33,3 +25,10 @@ merge_cmd () {
        "$merge_tool_path" "$BASE" "$LOCAL" "$REMOTE" "$MERGED"
        check_unchanged
 }
+
+create_empty_file () {
+       empty_file="${TMPDIR:-/tmp}/git-difftool-p4merge-empty-file.$$"
+       >"$empty_file"
+
+       printf "$empty_file"
+}