repack: respect kept objects with '--write-midx -b'

Historically, we needed a single packfile in order to have reachability
bitmaps. This introduced logic that when 'git repack' had a '-b' option
that we should stop sending the '--honor-pack-keep' option to the 'git
pack-objects' child process, ensuring that we create a packfile
containing all reachable objects.

In the world of multi-pack-index bitmaps, we no longer need to repack
all objects into a single pack to have valid bitmaps. Thus, we should
continue sending the '--honor-pack-keep' flag to 'git pack-objects'.

The fix is very simple: only disable the flag when writing bitmaps but
also _not_ writing the multi-pack-index.

This opens the door to new repacking strategies that might want to keep
some historical set of objects in a stable pack-file while only
repacking more recent objects.

To test, create a new 'test_subcommand_inexact' helper that is more
flexible than 'test_subcommand'. This allows us to look for the
--honor-pack-keep flag without over-indexing on the exact set of
arguments.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

2 files changed, 40 insertions, 0 deletions

diff --git a/t/t7700-repack.sh b/t/t7700-repack.sh
index 0260ad6f0e..63c9a247f5 100755
--- a/t/t7700-repack.sh
+++ b/t/t7700-repack.sh
@@ -372,4 +372,10 @@ test_expect_success '--write-midx with preferred bitmap tips' '
 	)
 '
 
+test_expect_success '--write-midx -b packs non-kept objects' '
+	GIT_TRACE2_EVENT="$(pwd)/trace.txt" \
+		git repack --write-midx -a -b &&
+	test_subcommand_inexact git pack-objects --honor-pack-keep <trace.txt
+'
+
 test_done
diff --git a/t/test-lib-functions.sh b/t/test-lib-functions.sh
index eef2262a36..5c623f0d5c 100644
--- a/t/test-lib-functions.sh
+++ b/t/test-lib-functions.sh
@@ -1749,6 +1749,40 @@ test_subcommand () {
 }
 
 # Check that the given command was invoked as part of the
+# trace2-format trace on stdin, but without an exact set of
+# arguments.
+#
+#	test_subcommand [!] <command> <args>... < <trace>
+#
+# For example, to look for an invocation of "git pack-objects"
+# with the "--honor-pack-keep" argument, use
+#
+#	GIT_TRACE2_EVENT=event.log git repack ... &&
+#	test_subcommand git pack-objects --honor-pack-keep <event.log
+#
+# If the first parameter passed is !, this instead checks that
+# the given command was not called.
+#
+test_subcommand_inexact () {
+	local negate=
+	if test "$1" = "!"
+	then
+		negate=t
+		shift
+	fi
+
+	local expr=$(printf '"%s".*' "$@")
+	expr="${expr%,}"
+
+	if test -n "$negate"
+	then
+		! grep "\"event\":\"child_start\".*\[$expr\]"
+	else
+		grep "\"event\":\"child_start\".*\[$expr\]"
+	fi
+}
+
+# Check that the given command was invoked as part of the
 # trace2-format trace on stdin.
 #
 #	test_region [!] <category> <label> git <command> <args>...