t5310: factor out bitmap traversal comparison

We check the results of "rev-list --use-bitmap-index" by comparing it to
the same traversal without the bitmap option. However, this is a little
tricky to do because of some output differences (see the included
comment for details). Let's pull this out into a helper function, since
we'll be adding some similar tests.

While we're at it, let's also try to confirm that the bitmap output did
indeed use bitmaps. Since the code internally falls back to the
non-bitmap path in some cases, the tests are at risk of becoming trivial
noops.

This is a bit fragile, as not all outputs will differ (e.g., looking at
only the commits from a fully-bitmapped pack will end up exactly the
same as the normal traversal order, since it also matches the pack
order). So we'll provide an escape hatch by which tests can disable this
check (which should only be used after manually confirming that bitmaps
kicked in).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t5310-pack-bitmaps.sh

@@ -81,13 +81,9 @@ rev_list_tests() {
 	'
 
 	test_expect_success "enumerate --objects ($state)" '
-		git rev-list --objects --use-bitmap-index HEAD >tmp &&
-		cut -d" " -f1 <tmp >tmp2 &&
-		sort <tmp2 >actual &&
-		git rev-list --objects HEAD >tmp &&
-		cut -d" " -f1 <tmp >tmp2 &&
-		sort <tmp2 >expect &&
-		test_cmp expect actual
+		git rev-list --objects --use-bitmap-index HEAD >actual &&
+		git rev-list --objects HEAD >expect &&
+		test_bitmap_traversal expect actual
 	'
 
 	test_expect_success "bitmap --objects handles non-commit objects ($state)" '

t/test-lib-functions.sh

@@ -1516,3 +1516,30 @@ test_set_port () {
 	port=$(($port + ${GIT_TEST_STRESS_JOB_NR:-0}))
 	eval $var=$port
 }
+
+# Compare a file containing rev-list bitmap traversal output to its non-bitmap
+# counterpart. You can't just use test_cmp for this, because the two produce
+# subtly different output:
+#
+#   - regular output is in traversal order, whereas bitmap is split by type,
+#     with non-packed objects at the end
+#
+#   - regular output has a space and the pathname appended to non-commit
+#     objects; bitmap output omits this
+#
+# This function normalizes and compares the two. The second file should
+# always be the bitmap output.
+test_bitmap_traversal () {
+	if test "$1" = "--no-confirm-bitmaps"
+	then
+		shift
+	elif cmp "$1" "$2"
+	then
+		echo >&2 "identical raw outputs; are you sure bitmaps were used?"
+		return 1
+	fi &&
+	cut -d' ' -f1 "$1" | sort >"$1.normalized" &&
+	sort "$2" >"$2.normalized" &&
+	test_cmp "$1.normalized" "$2.normalized" &&
+	rm -f "$1.normalized" "$2.normalized"
+}