Show warning if package.json uses local (file:) packages

[mrseanryan]

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

What is the current behavior?

yarn does install local (file:) packages, but there is a known bug #6037 which makes using such packages a bit difficult, since it is pretty easy to fill up a whole disk with the yarn cache.

example from package.json:

  "devDependencies": {
    "basic-parser": "file:../parsers/basic-parser",
   }

where ../parsers/basic-parser points to another folder that contains another package.json

See #6037 for more details.

What is the expected behavior?

The new feature would be to show a warning if the package.json file contains file:.... packages.
Then the user will know there is a problem, and they can either decide to:

a) stop using local packages
OR
b) switch to another solution (like npm, although that approach can also have issues...)

The goal is to save people time, as currently a user can fill up their whole disk with yarn cache, before investigating and discovering the problem (#6037).

Also, adding a warning could be a simple temporary solution (assuming #6037 is not easy to fix).

Please mention your node.js, yarn and operating system version.
yarn: 1.19.1
node: 12.11.0
OS: Ubuntu 18.04