[BUG] npm ci ignores the os field of package.json

[guidobouman]

What / Why

Executing npm ci ignores the os field in package.json. This causes platform specific packages like fsevents (macOS-only) to be installed on other platforms (Windows in this case).

When

• Every install through npm ci

Where

• Packages with the os field specified in package.json

How

Current Behavior

• See description

Steps to Reproduce

1. Run npm init in a new directory on a windows machine
2. Install a package with a deeply nested optional dependency on fsevents, like webpack: npm i webpack
3. Notice a package-lock.json is created with an optional dependency on fsevents@1.2.11
4. Remove node_modules te create a clean CI clone state
5. Run npm ci
6. See the installation fail because fsevents is downloaded, installed, and node-gyp is executed as a result.

Expected Behavior

• fsevents is skipped as the package is unsupported on Windows.

Who

• @pipobscure
• @paulmillr

References

• windows: fsevents v1 is getting built  fsevents/fsevents#301

[guidobouman]

Seems like this is a duplicate of #558.