No functional change or fixes here, just tidier code:
* prefer Path.exists()
* typechecking - NormalizedNames from poetry-core
* clean up some unnecessary duplication
* minor refactor
* gather the pyproject.toml parsing into one block, save a level of indentation
* remove more dead code
* simplify handling of extras at command line
* more abstract types 

# Pull Request Check List

- [ ] Added **tests** for changed code.
- [ ] Updated **documentation** for changed code.

Bunch of improvements over `Configuration` documentation:
- Better show default value of options
- Add some missing `Introduced in <VERSION>` notes
- Add backticks around types for better readability

Will backport to `1.2` branch before final release.

test(installer): use locked version of vcs dependency without reference (branch, tag, rev) instead of latest

Requires: python-poetry/poetry-core#449

Co-authored-by: Bjorn Neergaard <bjorn@neersighted.com>

`cleo.terminal.Terminal` was replaced in https://github.com/python-poetry/cleo/pull/175 in favor of `shutil.get_terminal_size`

At the moment a venv is created on running a `poetry self` command. Even if it is not used in the command itself it's unnecessary and lead to problems as reported in #6222. This PR fixes this.

Resolves: #6222

# Pull Request Check List

Resolves: #3097 

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- [x] Added **tests** for changed code. I adapted the test in the `tests/console/commands/plugin/test_remove.py` file to reflect the bug fix.
- [ ] Updated **documentation** for changed code.

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Apart from running the ci linting steps and pytest locally for both python 3.6 and 3.8, I also tested the code by running
```
docker run --rm -i --entrypoint bash python:3.8 <<EOF
set -e
python -m pip install -q git+https://github.com/mmacchia/poetry.git@issue/3097
python -m poetry new foobar
pushd foobar
sed -i /pytest/d pyproject.toml
python -m poetry add --dry-run pycowsay
python -m poetry run pip list
EOF
```
The corresponding output is:
```
Created package foobar in foobar
/foobar /
Creating virtualenv foobar-lWDpn5M1-py3.8 in /root/.cache/pypoetry/virtualenvs
Using version ^0.0.0.1 for pycowsay

Updating dependencies
Resolving dependencies...

Writing lock file

Package operations: 1 install, 0 updates, 0 removals

  • Installing pycowsay (0.0.0.1)
Package    Version
---------- -------
pip        21.2.4
setuptools 58.1.0
wheel      0.37.0
```
As expected, the command `poetry add --dry-run pycowsay` yielded a single output (` • Installing pycowsay (0.0.0.1)`) and did not add the package to the project (see the output of `poetry run pip list`).

The change in the PR solves the duplication issue because the creation of the console output when `not self._enabled` is taken care of by the boolean output of the`self._should_write_operation(operation)` function.

Please feel free to get in touch if I can help adding more test cases for the `--dry-run` argument or the `_enabled` flag and to add any feedback. I would be happy to improve/clarify the code in this PR.

Co-authored-by: Marco Macchia <mmacchia@wayfair.com>

This change improves the consistency of `Pool().remove_repository()` to make it easier to write poetry plugins which mutate the repository pool.

1.  Deleting an element from the middle of `Pool()._repositories` decrements the index of later entries.  Update `Pool()._lookup` to reflect this.

2.  If a primary repository is deleted, decrement `Pool()._secondary_start_idx` to ensure that any additional primary repositories are still added before all secondary repositories.

3.  If the default repository is deleted, reset `Pool()._default` so a new one can be added.

Co-authored-by: Randy Döring <30527984+radoering@users.noreply.github.com>

Co-authored-by: Bjorn Neergaard <bjorn@neersighted.com>

* test(commands): add tests for `shell`

* refactor(commands/shell): move venv check to dedicated function

* feat(commands/shell): replace `strtobool` with simpler check

Co-authored-by: Xinyuan Chen <45612704+tddschn@users.noreply.github.com>

* test(commands/shell): add tests for `_is_venv_activated`

* chore(cirrus): explicitly set `SHELL` env var

Co-authored-by: Xinyuan Chen <45612704+tddschn@users.noreply.github.com>
Co-authored-by: Bartosz Sokorski <b.sokorski@gmail.com>

* add checking for env variable in pypi token getter

* add unit tests for env pypi token

* add checking for env variable in pypi token getter

* add unit tests for env pypi token

* add info to the changelog

* refactor the structure

* fix unit tests

* undo changelog addition

* change docstring format to sphinx

* delete uncrsy unit test

* Delete unscry funtion call

Co-authored-by: Bjorn Neergaard <bjorn@neersighted.com>

* Update src/poetry/utils/password_manager.py

Co-authored-by: Bartosz Sokorski <b.sokorski@gmail.com>

* fix unit tests

* lol

* fix type hints

Co-authored-by: Bjorn Neergaard <bjorn@neersighted.com>
Co-authored-by: Bartosz Sokorski <b.sokorski@gmail.com>

Co-authored-by: Bartosz Sokorski <b.sokorski@gmail.com>

feat: fallback to gather metadata via pep517 if reading as Poetry project raises RuntimeError (#5834)

* feat: fallback to gather metadata via pep517 if reading as Poetry project raises RuntimeError

* test: added tests for fallback to gather metadata via pep517

* remove unnecessary annotations

* os.path.relpath accepts a Path

* simpler handling and typechecking of cachecontrol

* remove unneeded type assertion

* os.path.exists accepts a Path

* tighten the handling of env on commands

* tighten handling of installer on commands

* tighten handling of environment in poetry shell

* tighten typechecking in authenticator

build(deps): explicitly depend on `jsonschema`

Co-authored-by: Bartosz Sokorski <b.sokorski@gmail.com>

* build(deps): bump `mypy` to `0.971`

* build(deps): bump `types-*` packages

* chore: run `poetry lock`

* chore(utils): remove obsolete `# type: ignore`

* test(locker): add test to ensure sorted order

* fix(locker): sort dependencies of extras

* fix(locker): sort extras

* test(installation): remove obsolete `deepDiff`