B023:  Functions defined inside a loop must not use variables redefined in the loop, because late-binding closures are a classic gotcha.

Here's some sample code approximating the poetry code:
```python
#!/usr/bin/env python3


def one() -> int:
    return 1


def two() -> int:
    return 2


def three() -> int:
    return 3


factories = [one, two, three]

registered = []
for factory in factories:
    registered.append(lambda: factory())

for registered_factory in registered:
    print(f"result is {registered_factory()}")
```
output is
```
result is 3
result is 3
result is 3
```
which is exactly the gotcha that flake8-bugbear's B023 was trying to warn about.

I've applied one of the workarounds that various parts of the internet recommend, and you can verify for yourself if you're so inclined that doing the same in the toy script gives the expected output.

refactor(provider): remove unused parameter "env" (environment must always be set via contextmanager "use_environment" to avoid inconsistent python_constraint)

refactor(solver): remove unnecessary parameter "provider" (was only used in tests and can cause inconsistencies between a solver and its provider)

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

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

eg with this dependency
```
pyscf = { git = "https://github.com/pyscf/pyscf", tag = "v2.0.1"}
```
the cloning of submodules fails - because that project has messed up and not committed the file saying what revision they want of the `doc` submodule.

Legacy git client just silently carries on, so I've done the same here.

- regular depth-first search already handles circular dependencies and
  hitting the same package twice
  - the special cases might have saved a teensy amount of work, but the
    simplification is preferable

- pre-release handling here was not consistent with code elsewhere, and
  since "elsewhere" happens first, it wins
  - given a constraint like ">=1.0" the removed code would have allowed
    1.0rc1, but elsewhere in the codebase constraints are taken to mean
    what they say

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 

<!-- This is just a reminder about the most common mistakes. Please make sure that you tick all *appropriate* boxes.  But please read our [contribution guide](https://python-poetry.org/docs/contributing/) at least once, it will save you unnecessary review cycles! -->

- [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