No module named 'importlib_metadata' with python3.8

• I am on the latest Poetry version.
• I have searched the issues of this repo and believe that this is not a duplicate.
• If an exception occurs when executing a command, I executed it again in debug mode (-vvv option).

• OS version and name: Linux
• Poetry version: `1.0.0b2
• Link of a Gist with the contents of your pyproject.toml file: https://github.com/sobolevn/flake8-positional-only/blob/5672a153ba6e0ca89e7396fd18669c8697709cca/pyproject.toml

Issue

When I run poetry run with python3.8 I get this error:

0.25s$ poetry run flake8 .
Traceback (most recent call last):
  File "/home/travis/virtualenv/python3.8.0/bin/poetry", line 5, in <module>
    from poetry.console import main
  File "/home/travis/virtualenv/python3.8.0/lib/python3.8/site-packages/poetry/console/__init__.py", line 1, in <module>
    from .application import Application
  File "/home/travis/virtualenv/python3.8.0/lib/python3.8/site-packages/poetry/console/application.py", line 7, in <module>
    from .commands import AboutCommand
  File "/home/travis/virtualenv/python3.8.0/lib/python3.8/site-packages/poetry/console/commands/__init__.py", line 4, in <module>
    from .check import CheckCommand
  File "/home/travis/virtualenv/python3.8.0/lib/python3.8/site-packages/poetry/console/commands/check.py", line 1, in <module>
    from poetry.factory import Factory
  File "/home/travis/virtualenv/python3.8.0/lib/python3.8/site-packages/poetry/factory.py", line 15, in <module>
    from .json import validate_object
  File "/home/travis/virtualenv/python3.8.0/lib/python3.8/site-packages/poetry/json/__init__.py", line 4, in <module>
    import jsonschema
  File "/home/travis/virtualenv/python3.8.0/lib/python3.8/site-packages/jsonschema/__init__.py", line 31, in <module>
    import importlib_metadata
ModuleNotFoundError: No module named 'importlib_metadata'

Link to the CI: https://travis-ci.org/sobolevn/flake8-positional-only/jobs/600167655#L368

I have tried to:

1. Run poetry with -vvv - no change in the result
2. Install importlib_metadata manually inside the venv and the root system
3. Install poetry via pip and via curl (curl has different issue, see #1377)

No luck.

[decathorpe]

This is probably caused by a typo in this line: https://github.com/sdispater/poetry/blob/481d81d/pyproject.toml#L58

It should be < 3.8, not <= 3.8.

[florimondmanca]

Also experimenting this issue on Python 3.8.0 / TravisCI: https://travis-ci.com/florimondmanca/ddtrace-asgi/jobs/252426060

I managed to fix the issue by installing using the latest Poetry version via get-poetry.py:

before_install:
  - curl -sSL https://raw.githubusercontent.com/sdispater/poetry/master/get-poetry.py > get-poetry.py
  - python get-poetry.py -y --version 1.0.0b3
  - source ~/.poetry/env

install:
  - poetry install -v

Successful build here: https://travis-ci.com/florimondmanca/ddtrace-asgi/jobs/252427083

Not sure what the origin of the issue is, nor why it is only affecting 3.8 — perhaps a clash between importlib_metadata / importlib.metadata / Poetry’s own vendorized dependencies?