ref-filter.c: sort formatted dates by byte value

Update the ref sorting functions of 'ref-filter.c' so that when date fields
are specified with a format string (such as in 'git for-each-ref
--sort=creatordate:<something>'), they are sorted by their formatted string
value rather than by the underlying numeric timestamp. Currently, date
fields are always sorted by timestamp, regardless of whether formatting
information is included in the '--sort' key.

Leaving the default (unformatted) date sorting unchanged, sorting by the
formatted date string adds some flexibility to 'for-each-ref' by allowing
for behavior like "sort by year, then by refname within each year" or "sort
by time of day". Because the inclusion of a format string previously had no
effect on sort behavior, this change likely will not affect existing usage
of 'for-each-ref' or other ref listing commands.

Additionally, update documentation & tests to document the new sorting
mechanism.

Signed-off-by: Victoria Dye <vdye@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 46 insertions, 0 deletions

diff --git a/t/t6300-for-each-ref.sh b/t/t6300-for-each-ref.sh
index 843a7fe143..eb6c8204e8 100755
--- a/t/t6300-for-each-ref.sh
+++ b/t/t6300-for-each-ref.sh
@@ -1356,6 +1356,52 @@ test_expect_success '--no-sort without subsequent --sort prints expected refs' '
 	test_cmp expected actual
 '
 
+test_expect_success 'set up custom date sorting' '
+	# Dates:
+	# - Wed Feb 07 2024 21:34:20 +0000
+	# - Tue Dec 14 1999 00:05:22 +0000
+	# - Fri Jun 04 2021 11:26:51 +0000
+	# - Mon Jan 22 2007 16:44:01 GMT+0000
+	i=1 &&
+	for when in 1707341660 945129922 1622806011 1169484241
+	do
+		GIT_COMMITTER_DATE="@$when +0000" \
+		GIT_COMMITTER_EMAIL="user@example.com" \
+		git tag -m "tag $when" custom-dates-$i &&
+		i=$(($i+1)) || return 1
+	done
+'
+
+test_expect_success 'sort by date defaults to full timestamp' '
+	cat >expected <<-\EOF &&
+	945129922 refs/tags/custom-dates-2
+	1169484241 refs/tags/custom-dates-4
+	1622806011 refs/tags/custom-dates-3
+	1707341660 refs/tags/custom-dates-1
+	EOF
+
+	git for-each-ref \
+		--format="%(creatordate:unix) %(refname)" \
+		--sort=creatordate \
+		"refs/tags/custom-dates-*" >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'sort by custom date format' '
+	cat >expected <<-\EOF &&
+	00:05:22 refs/tags/custom-dates-2
+	11:26:51 refs/tags/custom-dates-3
+	16:44:01 refs/tags/custom-dates-4
+	21:34:20 refs/tags/custom-dates-1
+	EOF
+
+	git for-each-ref \
+		--format="%(creatordate:format:%H:%M:%S) %(refname)" \
+		--sort="creatordate:format:%H:%M:%S" \
+		"refs/tags/custom-dates-*" >actual &&
+	test_cmp expected actual
+'
+
 test_expect_success 'do not dereference NULL upon %(HEAD) on unborn branch' '
 	test_when_finished "git checkout main" &&
 	git for-each-ref --format="%(HEAD) %(refname:short)" refs/heads/ >actual &&