From 5e6fb37646d7d04465c3cd094f724228e2078639 Mon Sep 17 00:00:00 2001
From: Jukka Kurkela <jukka.kurkela@gmail.com>
Date: Tue, 14 Jan 2020 02:33:25 +0200
Subject: [PATCH] Detect stack change (#6947)

* Detect stack change
* Add test
---
 src/core/core.datasetController.js         | 19 +++++++++-
 test/specs/core.datasetController.tests.js | 44 ++++++++++++++++++++++
 2 files changed, 62 insertions(+), 1 deletion(-)

diff --git a/src/core/core.datasetController.js b/src/core/core.datasetController.js
index c240d7844..db0bcd736 100644
--- a/src/core/core.datasetController.js
+++ b/src/core/core.datasetController.js
@@ -443,13 +443,30 @@ helpers.extend(DatasetController.prototype, {
 		const labelsChanged = me._labelCheck();
 		const scaleChanged = me._scaleCheck();
 		const meta = me._cachedMeta;
+		const dataset = me.getDataset();
+		let stackChanged = false;
 
 		// make sure cached _stacked status is current
 		meta._stacked = isStacked(meta.vScale, meta);
 
+		// detect change in stack option
+		if (meta.stack !== dataset.stack) {
+			stackChanged = true;
+			// remove values from old stack
+			meta._parsed.forEach(function(parsed) {
+				delete parsed._stacks[meta.vScale.id][meta.index];
+			});
+			meta.stack = dataset.stack;
+		}
+
 		// Re-sync meta data in case the user replaced the data array or if we missed
 		// any updates and so make sure that we handle number of datapoints changing.
-		me.resyncElements(dataChanged | labelsChanged | scaleChanged);
+		me.resyncElements(dataChanged | labelsChanged | scaleChanged | stackChanged);
+
+		// if stack changed, update stack values for the whole dataset
+		if (stackChanged) {
+			updateStacks(me, meta._parsed);
+		}
 	},
 
 	/**
diff --git a/test/specs/core.datasetController.tests.js b/test/specs/core.datasetController.tests.js
index 8d04dbee3..b69afb6c5 100644
--- a/test/specs/core.datasetController.tests.js
+++ b/test/specs/core.datasetController.tests.js
@@ -388,6 +388,50 @@ describe('Chart.DatasetController', function() {
 		expect(meta.yAxisID).toBe('secondYScaleID');
 	});
 
+	it('should re-synchronize stacks when stack is changed', function() {
+		var chart = acquireChart({
+			type: 'bar',
+			data: {
+				labels: ['a', 'b'],
+				datasets: [{
+					data: [1, 10],
+					stack: '1'
+				}, {
+					data: [2, 20],
+					stack: '2'
+				}, {
+					data: [3, 30],
+					stack: '1'
+				}]
+			}
+		});
+
+		expect(chart._stacks).toEqual({
+			'x.y.1.bar': {
+				0: {0: 1, 2: 3},
+				1: {0: 10, 2: 30}
+			},
+			'x.y.2.bar': {
+				0: {1: 2},
+				1: {1: 20}
+			}
+		});
+
+		chart.data.datasets[2].stack = '2';
+		chart.update();
+
+		expect(chart._stacks).toEqual({
+			'x.y.1.bar': {
+				0: {0: 1},
+				1: {0: 10}
+			},
+			'x.y.2.bar': {
+				0: {1: 2, 2: 3},
+				1: {1: 20, 2: 30}
+			}
+		});
+	});
+
 	it('should cleanup attached properties when the reference changes or when the chart is destroyed', function() {
 		var data0 = [0, 1, 2, 3, 4, 5];
 		var data1 = [6, 7, 8];
-- 
2.47.2