<h3 dir="auto">Current Behavior:</h3>

<p dir="auto">When a dependency is specified as dev dependency and as optional peer dependency, it is not installed.</p>
<h3 dir="auto">Expected Behavior:</h3>

<p dir="auto">I expect all dev dependencies to be installed.</p>
<h3 dir="auto">Steps To Reproduce:</h3>
<div class="snippet-clipboard-content notranslate position-relative overflow-auto" data-snippet-clipboard-copy-content="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
  run `npm fund` for details

found 0 vulnerabilities
luigi@ubuntu:~/ws$ npm ls utf-8-validate
ws@7.3.1 /home/luigi/ws
└── (empty)"><pre class="notranslate"><code class="notranslate">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
  run `npm fund` for details

found 0 vulnerabilities
luigi@ubuntu:~/ws$ npm ls utf-8-validate
ws@7.3.1 /home/luigi/ws
└── (empty)
</code></pre></div>
<h3 dir="auto">Environment:</h3>
<ul dir="auto">
<li>OS: Ubuntu 20.04</li>
<li>Node: 15.0.1</li>
<li>npm: 7.0.3</li>
</ul>
<h3 dir="auto">Current Behavior:</h3>
<p dir="auto">When a dependency is specified as a <code class="notranslate">devDependency</code> <strong>and</strong> as a <code class="notranslate">peerDependency</code>, it is not installed. I tested it with npm@7.0.2, everything worked well with npm &lt; 7.</p>
<h3 dir="auto">Expected Behavior:</h3>
<p dir="auto">I expect that all dev dependencies should be installed.</p>
<h3 dir="auto">Steps To Reproduce:</h3>
<p dir="auto">I created a very small repository to reproduce the issue, so you can just checkout it and install dependencies:</p>
<div class="snippet-clipboard-content notranslate position-relative overflow-auto" data-snippet-clipboard-copy-content="git clone git@github.com:mjeanroy/npm-7-bug-peer-dev.git
cd npm-7-bug-peer-dev
npm install"><pre class="notranslate"><code class="notranslate">git clone git@github.com:mjeanroy/npm-7-bug-peer-dev.git
cd npm-7-bug-peer-dev
npm install
</code></pre></div>
<h3 dir="auto">Environment:</h3>
<ul dir="auto">
<li>OS: MacOS 10.15.7</li>
<li>Node: 15.0.0</li>
<li>npm: 7.0.2</li>
</ul>