Can't forcefully `include` a specific polyfill with preset-env `useBuiltIns=usage`

Bug Report

According to doc, include should force the inclusion of a polyfill, even if useBuiltIns=usage, even if source code does not contains reference to the function.

Current Behavior

• Forcing polyfill inclusion in preset-env does not seem to work. The resulting code does not contain the polyfill and an error is thrown: Invalid Option: The plugins/built-ins '@babel/plugin-transform-object-assign' passed to the 'include' option are not valid. Please check data/[plugin-features|built-in-features].js in babel-preset-env

Input Code

• Any JS code that does not make use of Object.assign()

Expected behavior/code

• The code should contain the es6.object.assign (see below Babel configuration).

Babel Configuration (.babelrc, package.json, cli command)

{
    "plugins": [
	"@babel/plugin-transform-object-assign"
    ],
    "presets": [
	[
	    "@babel/preset-env",
	    {
		"useBuiltIns": "usage",
		"include": [
		    "@babel/plugin-transform-object-assign"
		]
	    }
	]
    ]
}

Environment

• Babel version(s): v7.1.2
• Node/npm version: Node 10.12.0/npm 6.4.1
• OS: Ubuntu 18.04
• Monorepo: yes
• How you are using Babel: browserify ( babelify ( ) )

Context

• I bundle a javascript source included in a website. But some additional javascript files provided by some webpage themselves may make use of ES6 functions. I would like to forcefully provide a couple of manually selected polyfills to the bundle.

[carloscuesta]

I’m facing the same issue and I don’t know if this the expected behaviour or it is a misunderstanding of the babel-preset-env docs.

According to babel-preset-env include docs this field on is used to:

So according to this statement I’m understanding that I can include a a core-js built in polyfill to be always present in my bundle. Like this:

"include": ["es.weak-set"]

However seems that this is not working.

Even though my code it’s not specifically requiring this polyfill. My use case is that an external node_modules dependency uses WeakSet and that needs to be polyfilled to support IE11.

So the only option I had to include the polyfill is to import it once on my application to be bundled with everything. Like if I was importing an external module.

import 'core-js/es/weak-set'

[gavinsharp]

@joacim-boive can you show the code where useBuiltIns: usage is not detecting Promise?

A common case of this is a dependency that just isn’t loaded via babel-loader (e.g. an external library in node_modules). So not really a Babel issue, but there aren’t really any clean workarounds if include doesn’t work (you need to either switch to useBuiltIns: entry, force the import by putting in a dummy reference somewhere in your code to the polyfilled object, or force the external library to be babel-loaded, which often causes other issues).