[Bug Report] inconsistent behaviour with a file: dependency

[shigma]

Do you want to request a feature or report a bug?

bug report

What is the current behavior?

root/
  package.json
  foo/
    index.js
    package.json

root/package.json:

{
  "dependencies": {
    "foo": "file:foo"
  }
}

root/foo/package.json

{
  "name": "foo",
  "version": "0.0.0",
  "main": "index.js"
}

If the current behavior is a bug, please provide the steps to reproduce.

• npm i generates a node_modules folder with a symlink of foo in it.
• yarn generates a node_modules folder with a copy of foo in it.

What is the expected behavior?

The result of yarn should be consistent with npm i.

Please mention your node.js, yarn and operating system version.

• node: 12.14.1
• yarn: 1.19.2
• os: windows 10

Also probably related to #1794