yarn add --ignore-optional fails when optional dep has failing postinstall

[anp]

Reproduction

On a freshly init'd project:

$ yarn add --ignore-optional optional-failure

The optional-failure package has an optional dependency on pkg-with-failing-postinstall.

Here's the full output from running this command on my machine:

$ yarn add --ignore-optional optional-failure
yarn add v0.22.0-1-exp
info No lockfile found.
[1/4] 🔍  Resolving packages...
[2/4] 🚚  Fetching packages...
[3/4] 🔗  Linking dependencies...
[4/4] 📃  Building fresh packages...
⠁
error /Users/adam/code/lololololol/node_modules/pkg-with-failing-postinstall: Command failed.
Exit code: 1
Command: sh
Arguments: -c node this-does-not-exist.js
Directory: /Users/adam/code/lololololol/node_modules/pkg-with-failing-postinstall
Output:
module.js:472
    throw err;
    ^

Error: Cannot find module '/Users/adam/code/lololololol/node_modules/pkg-with-failing-postinstall/this-does-not-exist.js'
    at Function.Module._resolveFilename (module.js:470:15)
    at Function.Module._load (module.js:418:25)
    at Module.runMain (module.js:605:10)
    at run (bootstrap_node.js:425:7)
    at startup (bootstrap_node.js:146:9)
    at bootstrap_node.js:540:3
info Visit https://yarnpkg.com/en/docs/cli/add for documentation about this command.

This produces an exit status of 1.

Expected Behavior

The --ignore-optional flag should allow optional postinstall scripts to fail and be handled the same way failing installs of optional deps are handled.

System information

I've reproduced this on two systems:

1. Node 6.9.1, yarn 0.21.3, Windows 10
2. Node 7.7.1, yarn 0.22.0-1 (with a couple of patches from master), Mac Sierra 10.12.3

[skevy]

cc @bestander @Daniel15 -- just wanted to flag this to ya'all because it's breaking create-react-native-app for a bunch of users (anyone who doesn't have node native tools installed).

[bestander]

Thanks, totally worth sending a PR and fixing it sooner.
Feel free to ping me there.

[bestander]

Fixed in 0.27