Merge branch 'ms/update-index-racy'

"git update-index --refresh" has been taught to deal better with
racy timestamps (just like "git status" already does).

* ms/update-index-racy:
  update-index: refresh should rewrite index in case of racy timestamps
  t7508: add tests capturing racy timestamp handling
  t7508: fix bogus mtime verification
  test-lib: introduce API for verifying file mtime

builtin/update-index.c

@@ -787,6 +787,17 @@ static int refresh(struct refresh_params *o, unsigned int flag)
 	setup_work_tree();
 	read_cache();
 	*o->has_errors |= refresh_cache(o->flags | flag);
+	if (has_racy_timestamp(&the_index)) {
+		/*
+		 * Even if nothing else has changed, updating the file
+		 * increases the chance that racy timestamps become
+		 * non-racy, helping future run-time performance.
+		 * We do that even in case of "errors" returned by
+		 * refresh_cache() as these are no actual errors.
+		 * cmd_status() does the same.
+		 */
+		active_cache_changed |= SOMETHING_CHANGED;
+	}
 	return 0;
 }
 

cache.h

@@ -889,6 +889,7 @@ void *read_blob_data_from_index(struct index_state *, const char *, unsigned lon
 #define CE_MATCH_IGNORE_FSMONITOR 0X20
 int is_racy_timestamp(const struct index_state *istate,
 		      const struct cache_entry *ce);
+int has_racy_timestamp(struct index_state *istate);
 int ie_match_stat(struct index_state *, const struct cache_entry *, struct stat *, unsigned int);
 int ie_modified(struct index_state *, const struct cache_entry *, struct stat *, unsigned int);
 

read-cache.c

@@ -2775,7 +2775,7 @@ static int repo_verify_index(struct repository *repo)
 	return verify_index_from(repo->index, repo->index_file);
 }
 
-static int has_racy_timestamp(struct index_state *istate)
+int has_racy_timestamp(struct index_state *istate)
 {
 	int entries = istate->cache_nr;
 	int i;

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

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

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
+}