git/rev_list_scanner: add --date-order

git/rev_list_scanner.go

@@ -37,6 +37,9 @@ const (
 	// results as given by git-rev-list(1) without any `--<t>-order`
 	// argument given. By default: reverse chronological order.
 	DefaultRevListOrder RevListOrder = iota
+	// DateRevListOrder gives the revisions such that no parents are shown
+	// before children, and otherwise in commit timestamp order.
+	DateRevListOrder
 )
 
 // ScanRefsOptions is an "options" type that is used to configure a scan
@@ -183,6 +186,11 @@ func revListArgs(l, r string, opt *ScanRefsOptions) (io.Reader, []string, error)
 	var stdin io.Reader
 	args := []string{"rev-list", "--objects"}
 
+	switch opt.Order {
+	case DateRevListOrder:
+		args = append(args, "--date-order")
+	}
+
 	switch opt.Mode {
 	case ScanRefsMode:
 		if opt.SkipDeletedBlobs {

git/rev_list_scanner_test.go

@@ -107,6 +107,13 @@ func TestRevListArgs(t *testing.T) {
 			},
 			ExpectedErr: "unknown scan type: -1",
 		},
+		"scan date order": {
+			Left: "left", Right: "right", Opt: &ScanRefsOptions{
+				Mode:  ScanRefsMode,
+				Order: DateRevListOrder,
+			},
+			ExpectedArgs: []string{"rev-list", "--objects", "--date-order", "--do-walk", "left", "right", "--"},
+		},
 	} {
 		t.Run(desc, c.Assert)
 	}