Support isoWeekday when rounding (#7269)

Author: kurkle

src/scales/scale.time.js

@@ -70,7 +70,7 @@ function parse(scale, input) {
 
 	const adapter = scale._adapter;
 	const options = scale.options.time;
-	const parser = options.parser;
+	const {parser, round, isoWeekday} = options;
 	let value = input;
 
 	if (typeof parser === 'function') {
@@ -88,8 +88,10 @@ function parse(scale, input) {
 		return value;
 	}
 
-	if (options.round) {
-		value = scale._adapter.startOf(value, options.round);
+	if (round) {
+		value = round === 'week' && isoWeekday
+			? scale._adapter.startOf(value, 'isoWeek', isoWeekday)
+			: scale._adapter.startOf(value, round);
 	}
 
 	return +value;

test/specs/scale.time.tests.js

@@ -486,6 +486,37 @@ describe('Time scale tests', function() {
 		expect(xScale.getLabelForValue(value)).toBe('Jan 1, 2015, 8:00:00 pm');
 	});
 
+	it('should round to isoWeekday', function() {
+		var chart = window.acquireChart({
+			type: 'line',
+			data: {
+				datasets: [{
+					data: [{x: '2020-04-12T20:00:00', y: 1}, {x: '2020-04-13T20:00:00', y: 2}]
+				}]
+			},
+			options: {
+				scales: {
+					x: {
+						type: 'time',
+						ticks: {
+							source: 'data'
+						},
+						time: {
+							unit: 'week',
+							round: 'week',
+							isoWeekday: 1,
+							displayFormats: {
+								week: 'WW'
+							}
+						}
+					},
+				}
+			}
+		});
+
+		expect(getLabels(chart.scales.x)).toEqual(['15', '16']);
+	});
+
 	it('should get the correct label for a timestamp', function() {
 		var chart = window.acquireChart({
 			type: 'line',