fix: return non 0 exit code if an error occurred

[andreialecu]

Was originally fixed in #633 but it doesn't seem to have survived the update to v5.

Non 0 exit code is required, otherwise Yarn 2 users may not see what went wrong.

[typicode]

Hi,

Thanks for the PR. Not sure it's still needed.

// index.js
throw new Error('foo')

{
 "scripts": {
    "postinstall": "node index.js"
  }
}

❯ yarn -v && yarn run postinstall
2.3.3
/tmp/test/index.js:1
throw new Error('foo')
^

Error: foo
    at Object.<anonymous> (/tmp/test/index.js:1:7)
    at Module._compile (internal/modules/cjs/loader.js:1063:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1092:10)
    at Module.load (internal/modules/cjs/loader.js:928:32)
    at Function.external_module_.Module._load (/tmp/test/.pnp.js:4738:14)
    at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:72:12)
    at internal/main/run_main_module.js:17:47

That said, I think that Yarn v2 doesn't run automatically "postinstall", you can check with "postinstall": "touch foo".

[andreialecu]

Yarn 2 does run postinstall but only when changes are detected, and it suppresses the output by default.

Try CI=true yarn rebuild and you can test it with

{
 "scripts": {
    "postinstall": "echo hello"
  }
}

Regarding why the PR is needed. It runs postinstall on yarn install, but it will not report any error unless you run it manually like in your example.

Note for Yarn 2 users postinstall won't run automatically, please run yarn run postinstall manually to enable hooks.

This mention in the documentation is not accurate, considering the above.

[typicode]

Yarn 2 does run postinstall but only when changes are detected, and it suppresses the output by default.

Thanks for the explanation, I've updated docs.

[typicode]

Closing as I think it's redundant, node index.js in the example above already exits with 1. But thanks for spotting the issue in the docs.