Allow tooltip callback override in dataset (#8640)

Author: kurkle

docs/docs/configuration/tooltip.md

@@ -102,24 +102,26 @@ Allows filtering of [tooltip items](#tooltip-item-context). Must implement at mi
 
 Namespace: `options.plugins.tooltip.callbacks`, the tooltip has the following callbacks for providing text. For all functions, `this` will be the tooltip object created from the `Tooltip` constructor.
 
+Namespace: `data.datasets[].tooltip.callbacks`, items marked with `Yes` in the column `Dataset override` can be overridden per dataset.
+
 All functions are called with the same arguments: a [tooltip item context](#tooltip-item-context). All functions must return either a string or an array of strings. Arrays of strings are treated as multiple lines of text.
 
-| Name | Arguments | Description
-| ---- | --------- | -----------
-| `beforeTitle` | `TooltipItem[], object` | Returns the text to render before the title.
-| `title` | `TooltipItem[], object` | Returns text to render as the title of the tooltip.
-| `afterTitle` | `TooltipItem[], object` | Returns text to render after the title.
-| `beforeBody` | `TooltipItem[], object` | Returns text to render before the body section.
-| `beforeLabel` | `TooltipItem, object` | Returns text to render before an individual label. This will be called for each item in the tooltip.
-| `label` | `TooltipItem, object` | Returns text to render for an individual item in the tooltip. [more...](#label-callback)
-| `labelColor` | `TooltipItem, Chart` | Returns the colors to render for the tooltip item. [more...](#label-color-callback)
-| `labelTextColor` | `TooltipItem, Chart` | Returns the colors for the text of the label for the tooltip item.
-| `labelPointStyle` | `TooltipItem, Chart` | Returns the point style to use instead of color boxes if usePointStyle is true (object with values `pointStyle` and `rotation`). Default implementation uses the point style from the dataset points. [more...](#label-point-style-callback)
-| `afterLabel` | `TooltipItem, object` | Returns text to render after an individual label.
-| `afterBody` | `TooltipItem[], object` | Returns text to render after the body section.
-| `beforeFooter` | `TooltipItem[], object` | Returns text to render before the footer section.
-| `footer` | `TooltipItem[], object` | Returns text to render as the footer of the tooltip.
-| `afterFooter` | `TooltipItem[], object` | Text to render after the footer section.
+| Name | Arguments | Dataset override | Description
+| ---- | --------- | ---------------- | -----------
+| `beforeTitle` | `TooltipItem[], object` | | Returns the text to render before the title.
+| `title` | `TooltipItem[], object` | | Returns text to render as the title of the tooltip.
+| `afterTitle` | `TooltipItem[], object` | | Returns text to render after the title.
+| `beforeBody` | `TooltipItem[], object` | | Returns text to render before the body section.
+| `beforeLabel` | `TooltipItem, object` | Yes | Returns text to render before an individual label. This will be called for each item in the tooltip.
+| `label` | `TooltipItem, object` | Yes | Returns text to render for an individual item in the tooltip. [more...](#label-callback)
+| `labelColor` | `TooltipItem, Chart` | Yes | Returns the colors to render for the tooltip item. [more...](#label-color-callback)
+| `labelTextColor` | `TooltipItem, Chart` | Yes | Returns the colors for the text of the label for the tooltip item.
+| `labelPointStyle` | `TooltipItem, Chart` | Yes | Returns the point style to use instead of color boxes if usePointStyle is true (object with values `pointStyle` and `rotation`). Default implementation uses the point style from the dataset points. [more...](#label-point-style-callback)
+| `afterLabel` | `TooltipItem, object` | Yes | Returns text to render after an individual label.
+| `afterBody` | `TooltipItem[], object` | | Returns text to render after the body section.
+| `beforeFooter` | `TooltipItem[], object` | | Returns text to render before the footer section.
+| `footer` | `TooltipItem[], object` | | Returns text to render as the footer of the tooltip.
+| `afterFooter` | `TooltipItem[], object` | | Text to render after the footer section.
 
 ### Label Callback
 

src/plugins/plugin.tooltip.js

@@ -350,6 +350,11 @@ function createTooltipContext(parent, tooltip, tooltipItems) {
   });
 }
 
+function overrideCallbacks(callbacks, context) {
+  const override = context && context.dataset && context.dataset.tooltip && context.dataset.tooltip.callbacks;
+  return override ? callbacks.override(override) : callbacks;
+}
+
 export class Tooltip extends Element {
   constructor(config) {
     super();
@@ -451,9 +456,10 @@ export class Tooltip extends Element {
         lines: [],
         after: []
       };
-      pushOrConcat(bodyItem.before, splitNewlines(callbacks.beforeLabel.call(me, context)));
-      pushOrConcat(bodyItem.lines, callbacks.label.call(me, context));
-      pushOrConcat(bodyItem.after, splitNewlines(callbacks.afterLabel.call(me, context)));
+      const scoped = overrideCallbacks(callbacks, context);
+      pushOrConcat(bodyItem.before, splitNewlines(scoped.beforeLabel.call(me, context)));
+      pushOrConcat(bodyItem.lines, scoped.label.call(me, context));
+      pushOrConcat(bodyItem.after, splitNewlines(scoped.afterLabel.call(me, context)));
 
       bodyItems.push(bodyItem);
     });
@@ -511,9 +517,10 @@ export class Tooltip extends Element {
 
     // Determine colors for boxes
     each(tooltipItems, (context) => {
-      labelColors.push(options.callbacks.labelColor.call(me, context));
-      labelPointStyles.push(options.callbacks.labelPointStyle.call(me, context));
-      labelTextColors.push(options.callbacks.labelTextColor.call(me, context));
+      const scoped = overrideCallbacks(options.callbacks, context);
+      labelColors.push(scoped.labelColor.call(me, context));
+      labelPointStyles.push(scoped.labelPointStyle.call(me, context));
+      labelTextColors.push(scoped.labelTextColor.call(me, context));
     });
 
     me.labelColors = labelColors;