Resync metasets array when indices change.

src/core/core.controller.js

@@ -195,6 +195,7 @@ helpers.extend(Chart.prototype, /** @lends Chart */ {
 		me.options = config.options;
 		me._bufferedRender = false;
 		me._layers = [];
+		me._metasets = [];
 
 		// Add the chart instance to the global namespace
 		Chart.instances[me.id] = me;
@@ -399,11 +400,45 @@ helpers.extend(Chart.prototype, /** @lends Chart */ {
 		scaleService.addScalesToLayout(this);
 	},
 
+	/**
+	 * Updates the given metaset with the given dataset index. Ensures it's stored at that index
+	 * in the _metasets array by swapping with the metaset at that index if necessary.
+	 * @param {Object} meta - the dataset metadata
+	 * @param {number} index - the dataset index
+	 * @private
+	 */
+	_updateMetasetIndex: function(meta, index) {
+		const metasets = this._metasets;
+		const oldIndex = meta.index;
+		if (oldIndex !== index) {
+			metasets[oldIndex] = metasets[index];
+			metasets[index] = meta;
+			meta.index = index;
+		}
+	},
+
+	/**
+	 * @private
+	 */
+	_updateMetasets: function() {
+		const me = this;
+		const metasets = me._metasets;
+		const numData = me.data.datasets.length;
+		const numMeta = metasets.length;
+
+		if (numMeta > numData) {
+			for (let i = numData; i < numMeta; ++i) {
+				me.destroyDatasetMeta(i);
+			}
+			metasets.splice(numData, numMeta - numData);
+		}
+		me._sortedMetasets = metasets.slice(0).sort(compare2Level('order', 'index'));
+	},
+
 	buildOrUpdateControllers: function() {
 		var me = this;
 		var newControllers = [];
 		var datasets = me.data.datasets;
-		var sorted = me._sortedMetasets = [];
 		var i, ilen;
 
 		for (i = 0, ilen = datasets.length; i < ilen; i++) {
@@ -417,7 +452,7 @@ helpers.extend(Chart.prototype, /** @lends Chart */ {
 			}
 			meta.type = type;
 			meta.order = dataset.order || 0;
-			meta.index = i;
+			me._updateMetasetIndex(meta, i);
 			meta.label = '' + dataset.label;
 			meta.visible = me.isDatasetVisible(i);
 
@@ -433,11 +468,9 @@ helpers.extend(Chart.prototype, /** @lends Chart */ {
 				meta.controller = new ControllerClass(me, i);
 				newControllers.push(meta.controller);
 			}
-			sorted.push(meta);
 		}
 
-		sorted.sort(compare2Level('order', 'index'));
-
+		me._updateMetasets();
 		return newControllers;
 	},
 
@@ -768,8 +801,8 @@ helpers.extend(Chart.prototype, /** @lends Chart */ {
 	getDatasetMeta: function(datasetIndex) {
 		const me = this;
 		const dataset = me.data.datasets[datasetIndex];
-		const metasets = me._metasets = me._metasets || [];
-		let meta = metasets[datasetIndex];
+		const metasets = me._metasets;
+		let meta = metasets.filter(x => x._dataset === dataset).pop();
 
 		if (!meta) {
 			meta = metasets[datasetIndex] = {
@@ -782,6 +815,7 @@ helpers.extend(Chart.prototype, /** @lends Chart */ {
 				yAxisID: null,
 				order: dataset.order || 0,
 				index: datasetIndex,
+				_dataset: dataset,
 				_parsed: []
 			};
 		}

test/specs/core.controller.tests.js

@@ -1276,4 +1276,75 @@ describe('Chart', function() {
 			]);
 		});
 	});
+
+	describe('metasets', function() {
+		beforeEach(function() {
+			this.chart = acquireChart({
+				type: 'line',
+				data: {
+					datasets: [
+						{label: '1', order: 2},
+						{label: '2', order: 1},
+						{label: '3', order: 4},
+						{label: '4', order: 3},
+					]
+				}
+			});
+		});
+		afterEach(function() {
+			const metasets = this.chart._metasets;
+			expect(metasets.length).toEqual(this.chart.data.datasets.length);
+			for (let i = 0; i < metasets.length; i++) {
+				expect(metasets[i].index).toEqual(i);
+				expect(metasets[i]._dataset).toEqual(this.chart.data.datasets[i]);
+			}
+		});
+		it('should build metasets array in order', function() {
+			const metasets = this.chart._metasets;
+			expect(metasets[0].order).toEqual(2);
+			expect(metasets[1].order).toEqual(1);
+			expect(metasets[2].order).toEqual(4);
+			expect(metasets[3].order).toEqual(3);
+		});
+		it('should build sorted metasets array in correct order', function() {
+			const metasets = this.chart._sortedMetasets;
+			expect(metasets[0].order).toEqual(1);
+			expect(metasets[1].order).toEqual(2);
+			expect(metasets[2].order).toEqual(3);
+			expect(metasets[3].order).toEqual(4);
+		});
+		it('should be moved when datasets are removed from begining', function() {
+			this.chart.data.datasets.splice(0, 2);
+			this.chart.update();
+			const metasets = this.chart._metasets;
+			expect(metasets[0].order).toEqual(4);
+			expect(metasets[1].order).toEqual(3);
+		});
+		it('should be moved when datasets are removed from middle', function() {
+			this.chart.data.datasets.splice(1, 2);
+			this.chart.update();
+			const metasets = this.chart._metasets;
+			expect(metasets[0].order).toEqual(2);
+			expect(metasets[1].order).toEqual(3);
+		});
+		it('should be moved when datasets are inserted', function() {
+			this.chart.data.datasets.splice(1, 0, {label: '1.5', order: 5});
+			this.chart.update();
+			const metasets = this.chart._metasets;
+			expect(metasets[0].order).toEqual(2);
+			expect(metasets[1].order).toEqual(5);
+			expect(metasets[2].order).toEqual(1);
+			expect(metasets[3].order).toEqual(4);
+			expect(metasets[4].order).toEqual(3);
+		});
+		it('should be replaced when dataset is replaced', function() {
+			this.chart.data.datasets.splice(1, 1, {label: '1.5', order: 5});
+			this.chart.update();
+			const metasets = this.chart._metasets;
+			expect(metasets[0].order).toEqual(2);
+			expect(metasets[1].order).toEqual(5);
+			expect(metasets[2].order).toEqual(4);
+			expect(metasets[3].order).toEqual(3);
+		});
+	});
 });