Fix ticks.mirror (#8482)

src/core/core.scale.js

@@ -1524,6 +1524,11 @@ export default class Scale extends Element {
 	 */
   _computeLabelArea() {
     const me = this;
+
+    if (me.options.ticks.mirror) {
+      return;
+    }
+
     const chart = me.chart;
     const position = me.options.position;
 
@@ -1532,8 +1537,6 @@ export default class Scale extends Element {
     } if (position === 'top' || position === 'bottom') {
       return {top: me.top, left: 0, bottom: me.bottom, right: chart.width};
     }
-
-    return null;
   }
 
   /**

test/fixtures/core.scale/ticks-mirror.js

@@ -0,0 +1,27 @@
+module.exports = {
+  config: {
+    type: 'line',
+    data: {
+      datasets: [{
+        data: [1, -1, 3],
+      }],
+      labels: ['Label1', 'Label2', 'Label3']
+    },
+    options: {
+      scales: {
+        y: {
+          ticks: {
+            mirror: true
+          }
+        }
+      }
+    }
+  },
+  options: {
+    spriteText: true,
+    canvas: {
+      height: 256,
+      width: 512
+    }
+  }
+};