Update "Unable to find installation candidates" to be more verbose

[jimmywan]

I recently ran into an issue where my credentials were misconfigured, but the error was the rather generic "Unable to find installation candidates".

Is there any way to add an explicit credentials test and/or have auth errors throw a different error?

When debugging things like CI/CD and/or multi-stage docker builds, it seems like that these types of credential errors are pretty common in new projects (1 letter typos) and/or new user env setups and the fact that it sounds like a set of misconfigured dependencies doesn't help things.

Example stack trace

Stack trace:

  5  /usr/local/lib/python3.8/site-packages/poetry/installation/executor.py:202 in _execute_operation
     result = self._do_execute_operation(operation)

  4  /usr/local/lib/python3.8/site-packages/poetry/installation/executor.py:276 in _do_execute_operation
     result = getattr(self, "_execute_{}".format(method))(operation)

  3  /usr/local/lib/python3.8/site-packages/poetry/installation/executor.py:411 in _execute_install
     return self._install(operation)

  2  /usr/local/lib/python3.8/site-packages/poetry/installation/executor.py:437 in _install
     archive = self._download(operation)

  1  /usr/local/lib/python3.8/site-packages/poetry/installation/executor.py:583 in _download
     link = self._chooser.choose_for(operation.package)

  RuntimeError

  Unable to find installation candidates for pyasn1 (0.4.8)

  at /usr/local/lib/python3.8/site-packages/poetry/installation/chooser.py:72 in choose_for
       68│ 
       69│             links.append(link)
       70│ 
       71│         if not links:
    →  72│             raise RuntimeError(
       73│                 "Unable to find installation candidates for {}".format(package)
       74│             )
       75│ 
       76│         # Get the best link


  Stack trace:

  5  /usr/local/lib/python3.8/site-packages/poetry/installation/executor.py:202 in _execute_operation
     result = self._do_execute_operation(operation)

  4  /usr/local/lib/python3.8/site-packages/poetry/installation/executor.py:276 in _do_execute_operation
     result = getattr(self, "_execute_{}".format(method))(operation)

  3  /usr/local/lib/python3.8/site-packages/poetry/installation/executor.py:411 in _execute_install
     return self._install(operation)

  2  /usr/local/lib/python3.8/site-packages/poetry/installation/executor.py:437 in _install
     archive = self._download(operation)

  1  /usr/local/lib/python3.8/site-packages/poetry/installation/executor.py:583 in _download
     link = self._chooser.choose_for(operation.package)

  RuntimeError

  Unable to find installation candidates for protobuf (3.20.1)

  at /usr/local/lib/python3.8/site-packages/poetry/installation/chooser.py:72 in choose_for
       68│ 
       69│             links.append(link)
       70│ 
       71│         if not links:
    →  72│             raise RuntimeError(
       73│                 "Unable to find installation candidates for {}".format(package)
       74│             )
       75│ 
       76│         # Get the best link