• I'd be willing to implement a fix

Describe the bug

When using "yarn pack" in Yarn v1, package.json variables (such as npm_package_version) are honoured. This seems to not be th case in yarn v2.

To Reproduce

I have a package.json which defines a "pack" script like so:

  "scripts": {
    "pack": "yarn pack --filename my-file-v$npm_package_version.tar.gz",
  }

The error when I run "yarn run pack" is Internal Error: Unbound variable "npm_package_version"

The minimal information needed to reproduce your issue (ideally a package.json with a single dep). Note that bugs without minimal reproductions might be closed.

Environment if relevant (please complete the following information):

• OS: Linux
• Node version 10.22.0
• Yarn version 2.1.1