fs: make BwTimetable.Set replace the timetable instead of appending to it

Set built the timetable with *x = append(*x, ts), so setting a bandwidth
timetable on a value that already held one kept both schedules. The single-value
branch of the same function has always done *x = BwTimetable{ts}, and the other
multi-token Set methods in this package build into a local and assign at the end.

The visible effect is through the rc API. The "main" options block registered in
fs.RegisterGlobalOptions is the live globalConfig, and options/set reshapes JSON
straight into it, so

  rclone rc options/set --json '{"main": {"BwLimit": "Mon-10:00,1Mi"}}'

added to the running daemon's timetable rather than replacing it, and the older
slot kept winning: LimitAt for a Sunday returned the previous 10Mi. The same
applies to a _config override on a single call, since AddConfig shallow-copies
the global.

Building into a local also stops a failed parse from leaving the previous
timetable partly overwritten, which the existing error cases already expect.

fs/bwtimetable.go

@@ -150,6 +150,8 @@ func (x *BwTimetable) Set(s string) error {
 		return nil
 	}
 
+	var newTimetable BwTimetable
+
 	// Split the timetable string by both spaces and semicolons
 	for tok := range strings.FieldsFuncSeq(s, func(r rune) bool {
 		return r == ' ' || r == ';'
@@ -178,7 +180,7 @@ func (x *BwTimetable) Set(s string) error {
 				if err := ts.Bandwidth.Set(tv[1]); err != nil {
 					return err
 				}
-				*x = append(*x, ts)
+				newTimetable = append(newTimetable, ts)
 			}
 		} else {
 			timespec := strings.Split(tv[0], "-")
@@ -205,9 +207,10 @@ func (x *BwTimetable) Set(s string) error {
 			if err := ts.Bandwidth.Set(tv[1]); err != nil {
 				return err
 			}
-			*x = append(*x, ts)
+			newTimetable = append(newTimetable, ts)
 		}
 	}
+	*x = newTimetable
 	return nil
 }
 

fs/bwtimetable_test.go

@@ -316,6 +316,52 @@ func TestBwTimetableSet(t *testing.T) {
 	}
 }
 
+func TestBwTimetableSetReplaces(t *testing.T) {
+	for _, test := range []struct {
+		first  string
+		second string
+		want   string
+	}{
+		{"Sun-00:00,10M", "Mon-10:00,1M", "Mon-10:00,1Mi"},
+		{"Mon-10:00,1M", "Mon-10:00,1M", "Mon-10:00,1Mi"},
+		{"Mon-10:00,1M", "2M", "2Mi"},
+		{"2M", "Mon-10:00,1M", "Mon-10:00,1Mi"},
+		{"11:00,333;13:40,666", "Mon-10:00,1M", "Mon-10:00,1Mi"},
+	} {
+		tt := BwTimetable{}
+		require.NoError(t, tt.Set(test.first), test.first)
+		require.NoError(t, tt.Set(test.second), test.second)
+		assert.Equal(t, test.want, tt.String(), "%q then %q", test.first, test.second)
+
+		var want BwTimetable
+		require.NoError(t, want.Set(test.second))
+		assert.Equal(t, want, tt, "%q then %q", test.first, test.second)
+	}
+}
+
+func TestBwTimetableSetErrorKeepsPrevious(t *testing.T) {
+	for _, in := range []string{
+		"Mon-11:00,333 bad",
+		"Mon-11:00,333 Tue-13:40,bad",
+		"Mon-11:00,333 24:01,666",
+		"11:00,333;bad",
+	} {
+		tt := BwTimetable{}
+		require.NoError(t, tt.Set("Sun-20:00,10M"))
+		require.Error(t, tt.Set(in), in)
+		assert.Equal(t, "Sun-20:00,10Mi", tt.String(), in)
+	}
+}
+
+func TestBwTimetableUnmarshalJSONReplaces(t *testing.T) {
+	var tt BwTimetable
+	require.NoError(t, json.Unmarshal([]byte(`"Sun-00:00,10M"`), &tt))
+	require.NoError(t, json.Unmarshal([]byte(`"Mon-10:00,1M"`), &tt))
+	assert.Equal(t, BwTimetable{
+		BwTimeSlot{DayOfTheWeek: 1, HHMM: 1000, Bandwidth: BwPair{Tx: 1024 * 1024, Rx: 1024 * 1024}},
+	}, tt)
+}
+
 func TestBwTimetableLimitAt(t *testing.T) {
 	for _, test := range []struct {
 		tt   BwTimetable