Keep the stack order when the first dataset of a stack is hidden

src/controllers/controller.bar.js

@@ -17,6 +17,25 @@ function getAllScaleValues(scale, type) {
   return scale._cache.$bar;
 }
 
+/**
+ * Returns the grouped metasets of the given type on the index scale, in sorted order.
+ * A hidden metaset is kept when its stack still has visible bars, so that it holds the
+ * position of that stack: hiding a dataset must not reorder the stacks.
+ * @private
+ */
+function getGroupedMetas(chart, iScale, type, hasBar) {
+  const axisID = iScale.axis + 'AxisID';
+  const metasets = chart._getSortedDatasetMetas()
+    .filter(meta => meta[axisID] === iScale.id && meta.type === type && meta.controller.options.grouped);
+
+  if (iScale.options.stacked === false) {
+    return metasets.filter(meta => meta.visible);
+  }
+
+  const visibleStacks = new Set(metasets.filter(meta => meta.visible && hasBar(meta)).map(meta => meta.stack));
+  return metasets.filter(meta => meta.visible || (meta.stack !== undefined && visibleStacks.has(meta.stack)));
+}
+
 /**
  * Computes the "optimal" sample size to maintain bars equally sized while preventing overlap.
  * @private
@@ -433,8 +452,6 @@ export default class BarController extends DatasetController {
 	 */
   _getStacks(last, dataIndex) {
     const {iScale} = this._cachedMeta;
-    const metasets = iScale.getMatchingVisibleMetas(this._type)
-      .filter(meta => meta.controller.options.grouped);
     const stacked = iScale.options.stacked;
     const stacks = [];
     const currentParsed = this._cachedMeta.controller.getParsed(dataIndex);
@@ -448,9 +465,10 @@ export default class BarController extends DatasetController {
         return true;
       }
     };
+    const metasets = getGroupedMetas(this.chart, iScale, this._type, meta => dataIndex === undefined || !skipNull(meta));
 
     for (const meta of metasets) {
-      if (dataIndex !== undefined && skipNull(meta)) {
+      if (meta.visible && dataIndex !== undefined && skipNull(meta)) {
         continue;
       }
 

test/specs/controller.bar.tests.js

@@ -326,6 +326,43 @@ describe('Chart.controllers.bar', function() {
     expect(meta.controller._getStackIndex(3)).toBe(1);
   });
 
+  it('should keep the stack order when the first dataset of a stack is hidden', function() {
+    var chart = window.acquireChart({
+      type: 'bar',
+      data: {
+        datasets: [
+          {data: [10, 20], stack: 'stack1'},
+          {data: [10, 20], stack: 'stack2'},
+          {data: [10, 20], stack: 'stack1'},
+          {data: [10, 20], stack: 'stack2'}
+        ],
+        labels: ['a', 'b']
+      },
+      options: {
+        scales: {
+          x: {
+            stacked: true
+          },
+          y: {
+            stacked: true
+          }
+        }
+      }
+    });
+
+    var getX = (datasetIndex) => chart.getDatasetMeta(datasetIndex).data[0].getProps(['x'], true).x;
+    expect(getX(2)).toBeLessThan(getX(3));
+
+    chart.hide(0);
+
+    var meta = chart.getDatasetMeta(1);
+    expect(meta.controller._getStackCount()).toBe(2);
+    expect(meta.controller._getStackIndex(1, 'stack2')).toBe(1);
+    expect(meta.controller._getStackIndex(2, 'stack1')).toBe(0);
+    expect(meta.controller._getStackIndex(3, 'stack2')).toBe(1);
+    expect(getX(2)).toBeLessThan(getX(3));
+  });
+
   it('should correctly get the stack index when a group is not specified', function() {
     var chart = window.acquireChart({
       type: 'bar',