[Bug] Changing area chart to step chart is not removing the area shading

[dirslashls]

Version

5.3.1

Link to Minimal Reproduction

No response

Steps to Reproduce

1. Go to https://echarts.apache.org/examples/en/editor.html?c=area-basic

2. At the end place the following code

setTimeout(() => {
  option.series.map(s => {
    s.step = 'end';
    delete s.areaStyle;
  });
  myChart.setOption(option,{ notMerge: true });
},4000);

Current Behavior

After the 4 seconds timeout, the chart changes to step line chart but the area shading is not removed.

Expected Behavior

The area shading should be removed.

Note that, if instead of setting the step to 'end', only the areaStyle is deleted, it does remove the area shading and show only the line chart as expected.

Environment

- OS:
- Browser:
- Framework:

Any additional comments?

No response

[jiawulin001]

This seems to be a bug.

Problem Analysis

The problem comes at Lineview.ts.
When notMerge is set to true, Echart tries rendering from scratch.
Echarts finds that 'step' has changed so it enters this if branch:

echarts/src/chart/line/LineView.ts

Lines 701 to 703 in 977bba1

	if (
	!(polyline && prevCoordSys.type === coordSys.type && step === this._step)
	) {

But when it comes to here:

echarts/src/chart/line/LineView.ts

Lines 729 to 733 in 977bba1

	if (isAreaChart) {
	polygon = this._newPolygon(
	points, stackedOnPoints
	);
	}

isAreaChart is false, but the polygon in the previous view is not cleared!

Note: Such situation is dealt with inside its else branch:

echarts/src/chart/line/LineView.ts

Lines 744 to 755 in 977bba1

	else {
	if (isAreaChart && !polygon) {
	// If areaStyle is added
	polygon = this._newPolygon(
	points, stackedOnPoints
	);
	}
	else if (polygon && !isAreaChart) {
	// If areaStyle is removed
	lineGroup.remove(polygon);
	polygon = this._polygon = null;
	}

Plan to fix

My plan is to add an else to dump polygon if isAreaChart is false.
Submitting a PR to solve this.

[dirslashls]

As I am trying the changing of chart types, I am noticing a few more discrepancies.

1. First bar chart and then change the type to 'pie'. The legend is not shown.
2. First pie chart with %age labels inside the sectors and then change the type to 'bar'/'line'/'area'. The data labels are showing.

I thought 'noMerge' is as good as completely replacing the old options with the new ones.