Allow category labels definition at scale level (chartjs#4506)

docs/axes/cartesian/category.md

@@ -1,13 +1,46 @@
 # Category Cartesian Axis
 
-The category scale will be familiar to those who have used v1.0. Labels are drawn from one of the label arrays included in the chart data. If only `data.labels` is defined, this will be used. If `data.xLabels` is defined and the axis is horizontal, this will be used. Similarly, if `data.yLabels` is defined and the axis is vertical, this property will be used. Using both `xLabels` and `yLabels` together can create a chart that uses strings for both the X and Y axes.
+If global configuration is used, labels are drawn from one of the label arrays included in the chart data. If only `data.labels` is defined, this will be used. If `data.xLabels` is defined and the axis is horizontal, this will be used. Similarly, if `data.yLabels` is defined and the axis is vertical, this property will be used. Using both `xLabels` and `yLabels` together can create a chart that uses strings for both the X and Y axes.
+
+Specifying any of the settings above defines the x axis as `type: category` if not defined otherwise. For more fine-grained control of category labels it is also possible to add `labels` as part of the category axis definition. Doing so does not apply the global defaults.
+
+## Category Axis Definition
+
+Globally:
+
+```javascript
+let chart = new Chart(ctx, {
+    type: ...
+    data: {
+        labels: ['January', 'February', 'March', 'April', 'May', 'June'],
+        datasets: ...
+    },
+});
+```
+As part of axis definition:
+
+```javascript
+let chart = new Chart(ctx, {
+    type: ...
+    data: ...
+    options: {
+        scales: {
+            xAxes: [{
+                type: 'category',
+                labels: ['January', 'February', 'March', 'April', 'May', 'June'],
+            }]
+        }
+    }
+});
+```
 
 ## Tick Configuration Options
 
 The category scale provides the following options for configuring tick marks. They are nested in the `ticks` sub object. These options extend the [common tick configuration](README.md#tick-configuration).
 
 | Name | Type | Default | Description
 | -----| ---- | --------| -----------
+| labels | Array[String] | - | An array of labels to display.
 | `min` | `String` | | The minimum item to display. [more...](#min-max-configuration)
 | `max` | `String` | | The maximum item to display. [more...](#min-max-configuration)
 

src/scales/scale.category.js

@@ -15,7 +15,7 @@ module.exports = function(Chart) {
 		*/
 		getLabels: function() {
 			var data = this.chart.data;
-			return (this.isHorizontal() ? data.xLabels : data.yLabels) || data.labels;
+			return this.options.labels || (this.isHorizontal() ? data.xLabels : data.yLabels) || data.labels;
 		},
 
 		determineDataLimits: function() {

test/specs/scale.category.tests.js

@@ -108,7 +108,7 @@ describe('Category scale tests', function() {
 		expect(scale.ticks).toEqual(mockData.xLabels);
 	});
 
-	it('Should generate ticks from the data xLabels', function() {
+	it('Should generate ticks from the data yLabels', function() {
 		var scaleID = 'myScale';
 
 		var mockData = {
@@ -136,6 +136,28 @@ describe('Category scale tests', function() {
 		expect(scale.ticks).toEqual(mockData.yLabels);
 	});
 
+	it('Should generate ticks from the axis labels', function() {
+		var labels = ['tick1', 'tick2', 'tick3', 'tick4', 'tick5'];
+		var chart = window.acquireChart({
+			type: 'line',
+			data: {
+				data: [10, 5, 0, 25, 78]
+			},
+			options: {
+				scales: {
+					xAxes: [{
+						id: 'x',
+						type: 'category',
+						labels: labels
+					}]
+				}
+			}
+		});
+
+		var scale = chart.scales.x;
+		expect(scale.ticks).toEqual(labels);
+	});
+
 	it ('should get the correct label for the index', function() {
 		var scaleID = 'myScale';