[PATCH 05/24] update-index: support backup log with --keep-backup

["Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>]

Since this is a plumbing command, backup log support remains off by
default and only active when both --keep-backup and core.backupLog=true
are specified.

The check of core.backupLog is mostly for convenient, the calling script
does not have to explicitly check core.backupLog every time it executes
update-index. Truly disabling backup log must be done with something
like

    git -c core.backupLog=false update-index ...

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 Documentation/git-update-index.txt |  3 +++
 builtin/update-index.c             |  7 +++++++
 t/t2080-backup-log.sh              | 11 +++++++++++
 3 files changed, 21 insertions(+)

diff --git a/Documentation/git-update-index.txt b/Documentation/git-update-index.txt
index 1c4d146a41..31fe330c88 100644
--- a/Documentation/git-update-index.txt
+++ b/Documentation/git-update-index.txt
@@ -218,6 +218,9 @@ will remove the intended effect of the option.
 	the configured value will take effect next time the index is
 	read and this will remove the intended effect of the option.
 
+--keep-backup::
+	Enable index backup log.
+
 \--::
 	Do not interpret any more arguments as options.
 
diff --git a/builtin/update-index.c b/builtin/update-index.c
index 31e7cce301..295b5f5277 100644
--- a/builtin/update-index.c
+++ b/builtin/update-index.c
@@ -28,6 +28,8 @@
 static int allow_add;
 static int allow_remove;
 static int allow_replace;
+static int update_backup_log;
+static int core_backup_log;
 static int info_only;
 static int force_remove;
 static int verbose;
@@ -289,6 +291,7 @@ static int add_one_path(const struct cache_entry *old, const char *path, int len
 	}
 	option = allow_add ? ADD_CACHE_OK_TO_ADD : 0;
 	option |= allow_replace ? ADD_CACHE_OK_TO_REPLACE : 0;
+	option |= update_backup_log && core_backup_log ? ADD_CACHE_LOG_UPDATES : 0;
 	if (add_cache_entry(ce, option)) {
 		discard_cache_entry(ce);
 		return error("%s: cannot add to the index - missing --add option?", path);
@@ -419,6 +422,7 @@ static int add_cacheinfo(unsigned int mode, const struct object_id *oid,
 		ce->ce_flags |= CE_VALID;
 	option = allow_add ? ADD_CACHE_OK_TO_ADD : 0;
 	option |= allow_replace ? ADD_CACHE_OK_TO_REPLACE : 0;
+	option |= update_backup_log && core_backup_log ? ADD_CACHE_LOG_UPDATES : 0;
 	if (add_cache_entry(ce, option))
 		return error("%s: cannot add to the index - missing --add option?",
 			     path);
@@ -969,6 +973,8 @@ int cmd_update_index(int argc, const char **argv, const char *prefix)
 			N_("let files replace directories and vice-versa"), 1),
 		OPT_SET_INT(0, "remove", &allow_remove,
 			N_("notice files missing from worktree"), 1),
+		OPT_SET_INT(0, "keep-backup", &update_backup_log,
+			N_("update index backup log if core.backupLog is set"), 1),
 		OPT_BIT(0, "unmerged", &refresh_args.flags,
 			N_("refresh even if index contains unmerged entries"),
 			REFRESH_UNMERGED),
@@ -1060,6 +1066,7 @@ int cmd_update_index(int argc, const char **argv, const char *prefix)
 		usage_with_options(update_index_usage, options);
 
 	git_config(git_default_config, NULL);
+	repo_config_get_bool(the_repository, "core.backupLog", &core_backup_log);
 
 	/* we will diagnose later if it turns out that we need to update it */
 	newfd = hold_locked_index(&lock_file, 0);
diff --git a/t/t2080-backup-log.sh b/t/t2080-backup-log.sh
index f7bdaaa3f6..6b3814c172 100755
--- a/t/t2080-backup-log.sh
+++ b/t/t2080-backup-log.sh
@@ -28,4 +28,15 @@ test_expect_success 'add writes backup log' '
 	test_cmp expected actual
 '
 
+test_expect_success 'update-index --keep-backup writes backup log' '
+	test_tick &&
+	echo update-index >>initial.t &&
+	OLD=$(git rev-parse :./initial.t) &&
+	git -c core.backupLog=true update-index --keep-backup initial.t &&
+	NEW=$(git hash-object initial.t) &&
+	echo "$OLD $NEW $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $test_tick -0700	initial.t" >expected &&
+	tail -n1 .git/index.bkl >actual &&
+	test_cmp expected actual
+'
+
 test_done
-- 
2.20.0.rc2.486.g9832c05c3d