[PATCH 1/1] read-cache: update index format default to v4

["Derrick Stolee via GitGitGadget" <gitgitgadget@gmail.com>]

From: Derrick Stolee <dstolee@microsoft.com>

The index v4 format has been available since 2012 with 9d22778
"reach-cache.c: write prefix-compressed names in the index". Since
the format has been stable for so long, almost all versions of Git
in use today understand version 4, removing one barrier to upgrade
-- that someone may want to downgrade and needs a working repo.

Despite being stable for a long time, this index version was never
adopted as the default. This prefix-compressed version of the format
can get significant space savings on repos with large working
directories (which naturally tend to have deep nesting). This version
is set as the default for some external tools, such as VFS for Git.
Because of this external use, the format has had a lot of "testing in
production" and also is subject to continuous integration in these
environments.

Previously, to test version 4 indexes, we needed to run the test
suite with GIT_TEST_INDEX_VERSION=4 (or TEST_GIT_INDEX_VERSION=4).

One potential, but short-term, downside is that we lose coverage of
the version 3 indexes. The trade-off is that we may want to cover
that version using GIT_TEST_INDEX_VERSION=3.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 read-cache.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/read-cache.c b/read-cache.c
index 372588260e..af6c8f2a67 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -1484,7 +1484,7 @@ struct cache_entry *refresh_cache_entry(struct cache_entry *ce,
  * Index File I/O
  *****************************************************************/
 
-#define INDEX_FORMAT_DEFAULT 3
+#define INDEX_FORMAT_DEFAULT 4
 
 static unsigned int get_index_format_default(void)
 {
-- 
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