title: How to create `dev_requirements.txt` from `extras_require` section of `setup.cfg` file using `pip-compile` from `pip-tools`?
body: <p>I use <a href="https://github.com/jazzband/pip-tools" rel="nofollow noreferrer">pip-tools</a> to manage my dependencies and environments which perfectly generates a <code>requirements.txt</code> file for my package that consists of a <code>setup.py</code> that looks like this:</p>
  <pre><code>#! /usr/bin/env python
  import os
  from setuptools import setup
  
  
  if &quot;CI_COMMIT_TAG&quot; in os.environ:
      VERSION = os.environ[&quot;CI_COMMIT_TAG&quot;]
  else:
      VERSION = &quot;0.0.0&quot;
  
  setup(version=VERSION)
  </code></pre>
  <p>and a <code>setup.cfg</code> like this:</p>
  <pre><code>...
  [options]
  python_requires = &gt;=3.7
  zip_safe = False
  packages = find:
  include_package_data = True
  install_requires =
      PyYAML
      Cython
      numpy==1.17.5
      pandas==0.25.3
      ...
  package_dir=
      foo=bar
  
  [options.extras_require]
  testing =
      tox&gt;=3.1.2
      pytest&gt;=3.4.0
  coverage =
      coverage
      pytest-cov&gt;=2.5.1
  other =
      anybadge
  ...
  </code></pre>
  <p>Running <code>$ pip-compile --index-url https://foo@bar@gitlab.my.host/api/v4/projects/236/packages/pypi/simple --no-header --allow-unsafe </code> yields my package requirements:</p>
  <pre><code>...
  async-timeout==3.0.1
      # via aiohttp
  attrs==21.2.0
      # via aiohttp
  bcrypt==3.2.0
  ...
  </code></pre>
  <p>But this only includes all the packages from the <code>install_requires</code> section of my <code>setup.cfg</code> file and not the requirements from <code>extras_require</code>. It should work with a <code>dev_requirements.in</code> file as described <a href="https://github.com/jazzband/pip-tools#workflow-for-layered-requirements" rel="nofollow noreferrer">here</a> but I would rather only use one configuration file.</p>
  <p>How can I create a separate <code>dev_requirements.txt</code> from this <code>extras_require</code> section of my <code>setup.cfg</code> file using <code>pip-compile</code> without having to create a <code>dev_requirements.in</code> file?</p>
  <p>Thanks in advance!</p>