[BUG] dev dependencies not installed if marked as optional peer dependencies

[lpinca]

Current Behavior:

When a dependency is specified as dev dependency and as optional peer dependency, it is not installed.

Expected Behavior:

I expect all dev dependencies to be installed.

Steps To Reproduce:

luigi@ubuntu:~/ws$ node -v
v15.0.1
luigi@ubuntu:~/ws$ npm -v
7.0.3
luigi@ubuntu:~$ git clone https://github.com/websockets/ws.git
Cloning into 'ws'...
remote: Enumerating objects: 14410, done.
remote: Total 14410 (delta 0), reused 0 (delta 0), pack-reused 14410
Receiving objects: 100% (14410/14410), 10.68 MiB | 969.00 KiB/s, done.
Resolving deltas: 100% (11804/11804), done.
luigi@ubuntu:~$ cd ws
luigi@ubuntu:~/ws$ npm i
npm WARN deprecated har-validator@5.1.5: this library is no longer supported
npm WARN deprecated request@2.88.2: request has been deprecated, see https://github.com/request/request/issues/3142

added 352 packages, and audited 352 packages in 25s

33 packages are looking for funding
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found 0 vulnerabilities
luigi@ubuntu:~/ws$ npm ls utf-8-validate
ws@7.3.1 /home/luigi/ws
└── (empty)

Environment:

• OS: Ubuntu 20.04
• Node: 15.0.1
• npm: 7.0.3

[ljharb]

Duplicate of #1998?

[lpinca]

It's not a duplicate. #1998 did not use optional peer dependencies and had omit=peer in .npmrc.

[lpinca]

Refs: nodejs/citgm#836

[lpinca]

A possible hint from #2005 (comment)

What's happening here is that we're loading the peer edge ahead of the dev edge, and then skipping it. And since the peer edge is optional, we don't install it. For the root project at least, dev should take priority, I agree, so this is a bug.

It could be fixed by npm/arborist#166.

[lpinca]

The issue was fixed in npm@7.0.4.