title: Poetry install fails with EnvCommandError: looks for version 2020.12.21.3-lambda, why?
body: <p>Poetry cannot complete any <code>install</code> or <code>add</code> without throwing an <code>EnvCommandError</code> having to do with not being able to find a <code>setup.py</code> for <code>soupsieve</code>.</p>
  <p>It looks for version &quot;2020.12.21.3-lambda&quot; and I don't understand why it's not loading the dependency from a remote source with a normal version like the other dependencies.</p>
  <pre><code>$ poetry update
  Updating dependencies
  Resolving dependencies... (54.1s)
  
  Writing lock file
  
  Package operations: 59 installs, 0 updates, 0 removals
  
    • Installing soupsieve (2020.12.21.3-lambda): Failed
  
    EnvCommandError
  
    Command ['/home/git/my-project/.venv/bin/pip', 'install', '--no-deps', 'file:///home/Library/Caches/pypoetry/artifacts/22/36/ca/c8aae41f80011be881aa337cc80abc25ffd8542471c325e4410afa86c8/authorities-deployer-2020.12.21.3-lambda.zip'] errored with the following return code 1, and output: 
   Looking in indexes: ... # censored proxy
    Processing /home/Library/Caches/pypoetry/artifacts/22/36/ca/c8aae41f80011be881aa337cc80abc25ffd8542471c325e4410afa86c8/authorities-deployer-2020.12.21.3-lambda.zip
        ERROR: Command errored out with exit status 1:
         command: /home/git/my-package/my-package/.venv/bin/python -c 'import sys, setuptools, tokenize; sys.argv[0] = '&quot;'&quot;'/private/var/folders/q6/xjd92kc90zsds149_rx08cy40000gp/T/pip-req-build-40kngare/setup.py'&quot;'&quot;'; __file__='&quot;'&quot;'/private/var/folders/q6/xjd92kc90zsds149_rx08cy40000gp/T/pip-req-build-40kngare/setup.py'&quot;'&quot;';f=getattr(tokenize, '&quot;'&quot;'open'&quot;'&quot;', open)(__file__);code=f.read().replace('&quot;'&quot;'\r\n'&quot;'&quot;', '&quot;'&quot;'\n'&quot;'&quot;');f.close();exec(compile(code, __file__, '&quot;'&quot;'exec'&quot;'&quot;'))' egg_info --egg-base /private/var/folders/q6/xjd92kc90zsds149_rx08cy40000gp/T/pip-pip-egg-info-02b8jxuf
             cwd: /private/var/folders/q6/xjd92kc90zsds149_rx08cy40000gp/T/pip-req-build-40kngare/
        Complete output (5 lines):
        Traceback (most recent call last):
          File &quot;&lt;string&gt;&quot;, line 1, in &lt;module&gt;
          File &quot;/usr/local/Cellar/python@3.9/3.9.0_5/Frameworks/Python.framework/Versions/3.9/lib/python3.9/tokenize.py&quot;, line 392, in open
            buffer = _builtin_open(filename, 'rb')
        FileNotFoundError: [Errno 2] No such file or directory: '/private/var/folders/q6/xjd92kc90zsds149_rx08cy40000gp/T/pip-req-build-40kngare/setup.py'
        ----------------------------------------
    ERROR: Command errored out with exit status 1: python setup.py egg_info Check the logs for full command output.
    WARNING: You are using pip version 20.3.1; however, version 20.3.3 is available.
    You should consider upgrading via the '/home/git/my-package/my-package/.venv/bin/python -m pip install --upgrade pip' command.
    
  
    at ~/.poetry/lib/poetry/utils/env.py:1074 in _run
        1070│                 output = subprocess.check_output(
        1071│                     cmd, stderr=subprocess.STDOUT, **kwargs
        1072│                 )
        1073│         except CalledProcessError as e:
      → 1074│             raise EnvCommandError(e, input=input_)
        1075│ 
        1076│         return decode(output)
        1077│ 
        1078│     def execute(self, bin, *args, **kwargs):
  
  </code></pre>
  <p>This package has worked just fine for some time. I don't remember changing anything in the <code>pyproject.toml</code>. <strong>I tried checking out an old version of <code>pyproject.toml</code> to see if maybe something had changed accidentally.</strong> Same result.</p>
  <p><strong>I also tried deleting the <code>.venv/</code> Poetry creates and recreating it.</strong> Same result.</p>
  <p>I have no idea where <code>soupsieve</code> is coming as a dependency. It installs just fine using plain old pip inside the environment poetry creates.</p>
  <pre><code>cd project/
  poetry shell
  pip install soupsieve # Installs 2.1 without a problem
  </code></pre>