3 files changed, 122 insertions, 5 deletions

diff --git a/t/t2108-update-index-refresh-racy.sh b/t/t2108-update-index-refresh-racy.sh
new file mode 100755
index 0000000000..bc5f2886fa
--- /dev/null
+++ b/t/t2108-update-index-refresh-racy.sh
@@ -0,0 +1,64 @@
+#!/bin/sh
+
+test_description='update-index refresh tests related to racy timestamps'
+
+TEST_PASSES_SANITIZE_LEAK=true
+. ./test-lib.sh
+
+reset_files () {
+	echo content >file &&
+	echo content >other &&
+	test_set_magic_mtime file &&
+	test_set_magic_mtime other
+}
+
+update_assert_changed () {
+	test_set_magic_mtime .git/index &&
+	test_might_fail git update-index "$1" &&
+	! test_is_magic_mtime .git/index
+}
+
+test_expect_success 'setup' '
+	reset_files &&
+	# we are calling reset_files() a couple of times during tests;
+	# test-tool chmtime does not change the ctime; to not weaken
+	# or even break our tests, disable ctime-checks entirely
+	git config core.trustctime false &&
+	git add file other &&
+	git commit -m "initial import"
+'
+
+test_expect_success '--refresh has no racy timestamps to fix' '
+	reset_files &&
+	# set the index time far enough to the future;
+	# it must be at least 3 seconds for VFAT
+	test_set_magic_mtime .git/index +60 &&
+	git update-index --refresh &&
+	test_is_magic_mtime .git/index +60
+'
+
+test_expect_success '--refresh should fix racy timestamp' '
+	reset_files &&
+	update_assert_changed --refresh
+'
+
+test_expect_success '--really-refresh should fix racy timestamp' '
+	reset_files &&
+	update_assert_changed --really-refresh
+'
+
+test_expect_success '--refresh should fix racy timestamp if other file needs update' '
+	reset_files &&
+	echo content2 >other &&
+	test_set_magic_mtime other &&
+	update_assert_changed --refresh
+'
+
+test_expect_success '--refresh should fix racy timestamp if racy file needs update' '
+	reset_files &&
+	echo content2 >file &&
+	test_set_magic_mtime file &&
+	update_assert_changed --refresh
+'
+
+test_done
diff --git a/t/t7508-status.sh b/t/t7508-status.sh
index 05c6c02435..2b7ef6c41a 100755
--- a/t/t7508-status.sh
+++ b/t/t7508-status.sh
@@ -1647,13 +1647,33 @@ test_expect_success '"Initial commit" should not be noted in commit template' '
 '
 
 test_expect_success '--no-optional-locks prevents index update' '
-	test-tool chmtime =1234567890 .git/index &&
+	test_set_magic_mtime .git/index &&
 	git --no-optional-locks status &&
-	test-tool chmtime --get .git/index >out &&
-	grep ^1234567890 out &&
+	test_is_magic_mtime .git/index &&
 	git status &&
-	test-tool chmtime --get .git/index >out &&
-	! grep ^1234567890 out
+	! test_is_magic_mtime .git/index
+'
+
+test_expect_success 'racy timestamps will be fixed for clean worktree' '
+	echo content >racy-dirty &&
+	echo content >racy-racy &&
+	git add racy* &&
+	git commit -m "racy test files" &&
+	# let status rewrite the index, if necessary; after that we expect
+	# no more index writes unless caused by racy timestamps; note that
+	# timestamps may already be racy now (depending on previous tests)
+	git status &&
+	test_set_magic_mtime .git/index &&
+	git status &&
+	! test_is_magic_mtime .git/index
+'
+
+test_expect_success 'racy timestamps will be fixed for dirty worktree' '
+	echo content2 >racy-dirty &&
+	git status &&
+	test_set_magic_mtime .git/index &&
+	git status &&
+	! test_is_magic_mtime .git/index
 '
 
 test_done
diff --git a/t/test-lib-functions.sh b/t/test-lib-functions.sh
index c3d38aaccb..85385d2ede 100644
--- a/t/test-lib-functions.sh
+++ b/t/test-lib-functions.sh
@@ -1840,3 +1840,36 @@ test_region () {
 test_readlink () {
 	perl -le 'print readlink($_) for @ARGV' "$@"
 }
+
+# Set mtime to a fixed "magic" timestamp in mid February 2009, before we
+# run an operation that may or may not touch the file.  If the file was
+# touched, its timestamp will not accidentally have such an old timestamp,
+# as long as your filesystem clock is reasonably correct.  To verify the
+# timestamp, follow up with test_is_magic_mtime.
+#
+# An optional increment to the magic timestamp may be specified as second
+# argument.
+test_set_magic_mtime () {
+	local inc=${2:-0} &&
+	local mtime=$((1234567890 + $inc)) &&
+	test-tool chmtime =$mtime "$1" &&
+	test_is_magic_mtime "$1" $inc
+}
+
+# Test whether the given file has the "magic" mtime set.  This is meant to
+# be used in combination with test_set_magic_mtime.
+#
+# An optional increment to the magic timestamp may be specified as second
+# argument.  Usually, this should be the same increment which was used for
+# the associated test_set_magic_mtime.
+test_is_magic_mtime () {
+	local inc=${2:-0} &&
+	local mtime=$((1234567890 + $inc)) &&
+	echo $mtime >.git/test-mtime-expect &&
+	test-tool chmtime --get "$1" >.git/test-mtime-actual &&
+	test_cmp .git/test-mtime-expect .git/test-mtime-actual
+	local ret=$?
+	rm -f .git/test-mtime-expect
+	rm -f .git/test-mtime-actual
+	return $ret
+}