[PATCH v4 1/2] auto gc: don't write bitmaps for incremental repacks

[David Turner <dturner@twosigma.com>]

When git gc --auto does an incremental repack of loose objects, we do
not expect to be able to write a bitmap; it is very likely that
objects in the new pack will have references to objects outside of the
pack.  So we shouldn't try to write a bitmap, because doing so will
likely issue a warning.

This warning was making its way into gc.log.  When the gc.log was
present, future auto gc runs would refuse to run.

Patch by Jeff King.
Bug report, test, and commit message by David Turner.

Signed-off-by: David Turner <dturner@twosigma.com>
Signed-off-by: Jeff King <peff@peff.net>
---
 builtin/gc.c  |  9 ++++++++-
 t/t6500-gc.sh | 25 +++++++++++++++++++++++++
 2 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/builtin/gc.c b/builtin/gc.c
index 069950d..331f219 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -191,6 +191,11 @@ static void add_repack_all_option(void)
 	}
 }
 
+static void add_repack_incremental_option(void)
+{
+       argv_array_push(&repack, "--no-write-bitmap-index");
+}
+
 static int need_to_gc(void)
 {
 	/*
@@ -208,7 +213,9 @@ static int need_to_gc(void)
 	 */
 	if (too_many_packs())
 		add_repack_all_option();
-	else if (!too_many_loose_objects())
+	else if (too_many_loose_objects())
+		add_repack_incremental_option();
+	else
 		return 0;
 
 	if (run_hook_le(NULL, "pre-auto-gc", NULL))
diff --git a/t/t6500-gc.sh b/t/t6500-gc.sh
index 5d7d414..def2aca 100755
--- a/t/t6500-gc.sh
+++ b/t/t6500-gc.sh
@@ -43,4 +43,29 @@ test_expect_success 'gc is not aborted due to a stale symref' '
 	)
 '
 
+test_expect_success 'auto gc with too many loose objects does not attempt to create bitmaps' '
+	test_config gc.auto 3 &&
+	test_config gc.autodetach false &&
+	test_config pack.writebitmaps true &&
+	# We need to create two object whose sha1s start with 17
+	# since this is what git gc counts.  As it happens, these
+	# two blobs will do so.
+	test_commit 263 &&
+	test_commit 410 &&
+	# Our first gc will create a pack; our second will create a second pack
+	git gc --auto &&
+	ls .git/objects/pack | grep -v bitmap | sort >existing_packs &&
+	test_commit 523 &&
+	test_commit 790 &&
+
+	git gc --auto 2>err &&
+	test_i18ngrep ! "^warning:" err &&
+	ls .git/objects/pack/ | grep -v bitmap | sort >post_packs &&
+	comm --output-delimiter , -1 -3 existing_packs post_packs >new &&
+	comm --output-delimiter , -2 -3 existing_packs post_packs >del &&
+	test_line_count = 0 del && # No packs are deleted
+	test_line_count = 2 new # There is one new pack and its .idx
+'
+
+
 test_done
-- 
2.8.0.rc4.22.g8ae061a