[BUG] npm fails to install optional dependencies of peer dependencies

[billyjanitsch]

Is there an existing issue for this?

• I have searched the existing issues

This issue exists in the latest npm version

• I am using the latest npm

Current Behavior

Suppose my package A depends on package B which peer-depends on package C which optionally depends on package D.

As of npm@11.5, npm install does not install D nor write it to the package lock.

This was introduced in #8431, which intended to prune optional peer dependencies. But optional peer dependencies are not the same as optional dependencies of peer dependencies, and this PR as written also affects the latter.

Expected Behavior

npm install should install D, as it did prior to npm@11.5.0.

Steps To Reproduce

1. Create a new package A which depends on package B which peer-depends on package C which optionally depends on package D.
2. Run npm install.
3. Observe that D does not exist in the package lock or node_modules.

Environment

• npm: 11.5.2
• Node.js: 22.18.0
• OS Name: macOS
• System Model Name: MacBook Pro
• npm config: default

[billyjanitsch]

(cc @G-Rath)

[chabb]

We've observing a similar behavior. One of the optional dependency of a dependency is incorrectly hoisted at the root level of the lockfile, and removed from the dependency.
This is not happening with 11.4.x.
This started happening on 11.5.x

[milaninfy]

Closing This looks like similer if not duplicate of #8464

[billyjanitsch]

@milaninfy that is not correct; these are distinct bugs. That bug is about optional peer dependencies. This bug is about optional dependencies of peer dependencies.