Setting platform dependant icon via electron-forge electronPackagerConfig - electron

Question

Using electron-forge to build a desktop app. The app is built for both OSX & Windows. Inside my package.json, I have:
"electronPackagerConfig": {
"icon": "src/images/icon/app_icon_osx.icns"
}
When I build on Windows, I'm having to manually change the icon in package.json from "app_icon_osx.icns" to "app_icon_win.ico".
If I try to just use "app_icon.png" for both platforms, the icon doesn't show on OSX, and the build fails with "rcedit.exe failed with exit code 1. Fatal error: Unable to set icon" on Windows.
I have all 3 versions of the icon (icns, ico, png) in a folder in the project. Because i'm using electron-forge, i don't seem to be able to use electron packager's --icon argument.
Is there a way I can pass the icon to use as a command line arg, instead of hardcoded in package.json? Or a way I can use the same png for both platforms?

Answer 1

The extension is automatically added for each platform. Just supply an icon per platform like this: app_icon.icns, app_icon.ico, ...
Then update your config:
"electronPackagerConfig": {
"icon": "src/images/icon/app_icon"
}

Answer 2

The accepted answer works for macOS and Windows, but for Linux you'll have to do something like this:
Set the app icon (for the app list only) in the maker:
{
name: "#electron-forge/maker-deb",
config: {
options: {
icon: "./src/images/icon.png",
},
},
},
Create an assets folder (or anything) an copy it during the build with the copy-webpack-plugin in your webpack.main.config.js:
const CopyPlugin = require("copy-webpack-plugin");
module.exports = {
// ...
plugins: [new CopyPlugin([{ from: "./assets", to: "assets" }])],
};
You can now access any files inside this folder from your main process, so reference the icon when creating your BrowserWindow as documented here
mainWindow = new BrowserWindow({
// ...
icon: path.join(__dirname, "assets/icon.png"),
});

Answer 3

In forge.config.js, do:
const path = require('path')
module.exports = {
packagerConfig: {
icon: path.join(__dirname, 'favicon'),
},
}
Important notes:
If the file extension is omitted, it is auto-completed to the correct extension based on the platform, including when platform: 'all' is in effect.
This setting doesn't change the icon when running electron-forge start.
If the setting is correct, and you still don't see the correct icon, you might have encountered the icon cache issue.
If on Windows 10, run ie4uinit -show in the command line will show the latest icon.