diff: don't read index when --no-index is given
authorThomas Gummerer <t.gummerer@gmail.com>
Wed, 11 Dec 2013 09:58:43 +0000 (10:58 +0100)
committerJunio C Hamano <gitster@pobox.com>
Thu, 12 Dec 2013 20:23:02 +0000 (12:23 -0800)
commit6df5762db354ca55a0cf77451d06b332b7de0b82
tree5f64e40da39f8969e1a34f04a993cbe0a453ec62
parent470faf96544c1844ad775c695dfa370fe0ef3756
diff: don't read index when --no-index is given

git diff --no-index ... currently reads the index, during setup, when
calling gitmodules_config().  This results in worse performance when the
index is not actually needed.  This patch avoids calling
gitmodules_config() when the --no-index option is given.  The times for
executing "git diff --no-index" in the WebKit repository are improved as
follows:

Test                      HEAD~3            HEAD
------------------------------------------------------------------
4001.1: diff --no-index   0.24(0.15+0.09)   0.01(0.00+0.00) -95.8%

An additional improvement of this patch is that "git diff --no-index" no
longer breaks when the index file is corrupt, which makes it possible to
use it for investigating the broken repository.

To improve the possible usage as investigation tool for broken
repositories, setup_git_directory_gently() is also not called when the
--no-index option is given.

Also add a test to guard against future breakages, and a performance
test to show the improvements.

Signed-off-by: Thomas Gummerer <t.gummerer@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
builtin/diff.c
t/perf/p4001-diff-no-index.sh [new file with mode: 0755]
t/t4053-diff-no-index.sh