chore: deprecate setHighlightMode (#19202)

docs/api/breaking-changes.md

@@ -152,6 +152,17 @@ app.enableMixedSandbox()
 
 Mixed-sandbox mode is now enabled by default.
 
+### `Tray`
+
+Under macOS Catalina our former Tray implementation breaks.
+Apple's native substitute doesn't support changing the highlighting behavior.
+
+```js
+// Deprecated
+tray.setHighlightMode(mode)
+// API will be removed in v7.0 without replacement.
+```
+
 ## Planned Breaking API Changes (5.0)
 
 ### `new BrowserWindow({ webPreferences })`

docs/api/tray.md

@@ -216,6 +216,8 @@ Returns `String` - the title displayed next to the tray icon in the status bar
 
 Sets when the tray's icon background becomes highlighted (in blue).
 
+**[Deprecated](breaking-changes.md#tray)**
+
 **Note:** You can use `highlightMode` with a [`BrowserWindow`](browser-window.md)
 by toggling between `'never'` and `'always'` modes when the window visibility
 changes.

lib/browser/api/tray.js

@@ -1,8 +1,12 @@
 'use strict'
 
 const { EventEmitter } = require('events')
+const { deprecate } = require('electron')
 const { Tray } = process.electronBinding('tray')
 
 Object.setPrototypeOf(Tray.prototype, EventEmitter.prototype)
 
+// Deprecations
+Tray.prototype.setHighlightMode = deprecate.removeFunction(Tray.prototype.setHighlightMode, 'setHighlightMode')
+
 module.exports = Tray