install-poetry.py fails to install poetry from tarball (using --path)

• 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: Docker image python:3.7-slim

• Poetry version: N/A

• Link of a Gist with the contents of your pyproject.toml file: N/A

Issue

To reproduce the environment exactly, everything below should be run within this docker container:

docker run --rm -it python:3.7-slim bash

On top of that, the following needs to be run within the docker container, before the 3 cases described below:

POETRY_VERSION=1.1.7
curl -LO https://github.com/python-poetry/poetry/releases/download/$POETRY_VERSION/poetry-$POETRY_VERSION-linux.tar.gz

Now, this works (old get-poetry.py install script, passing --file):

curl -s https://raw.githubusercontent.com/python-poetry/poetry/master/get-poetry.py | \
  python - --file poetry-$POETRY_VERSION-linux.tar.gz

And so does this (new install-poetry.py install script, passing --version):

curl -s https://raw.githubusercontent.com/python-poetry/poetry/master/install-poetry.py | \
  python - --version $POETRY_VERSION

But this (new install script, passing --path) claims to successfully install poetry, but actually installs an empty venv, without poetry:

curl -s https://raw.githubusercontent.com/python-poetry/poetry/master/install-poetry.py | \
  python - --path poetry-$POETRY_VERSION-linux.tar.gz

I make use of --path so that I can cache the tarball between docker builds & CI executions, so I'll have to stay on the deprecated get-poetry.py script for now 🙃

Start with install-poetry.py and reproduce the reported --path case in the python:3.7-slim Docker image using the Poetry 1.1.7 tarball. Compare its behavior with --version and the deprecated get-poetry.py --file path, then verify that the resulting virtual environment contains the poetry executable.