Don't install a package twice from cache

[yunxing]

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

What is the current behavior?
Some package installation are not idempotent. If you call post-install twice, the second installation may fail. Currently, after we install a package, we store the build artifacts in the cache. During the second installation, if we call postinstall on the package again, it may fail.

Repro
An example of this is ocamlRe. If you do

yarn install ocamlRe
rm -rf node_modules
yarn install ocamlRe 

the second installation will fail.

[LeiZeng]

I have the same question, which I don't think it's a "issue".

yarn install some-package
rm -rf node_modules/one-dependency

yarn check
# you can get the warning that the `one-dependency` is missing

yarn install
# success Already up-to-date.

yarn check
# you can get the warning that the `one-dependency` is missing

yarn install does not check the status first.

The solution is simple:
yarn install --force or yarn --force

Could be better if it can check and fix itself

[hpurmann]

I guess this should be closed as #805 is merged now?

[wyze]

Yup, thanks @hpurmann!