Reading the index into an empty file has been broken by
5a56da5806, since it causes the existing
index to always be loaded first, and dies if it's an empty file:
$ GIT_INDEX_FILE=`mktemp` git read-tree master
fatal: index file smaller than expected
It breaks for instance committing from git.el. This patch reverts to the
previous behavior of only loading the index when merging it.
Signed-off-by: Alexandre Julliard <julliard@winehq.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>