env: default to enabling pip/wheels/setuptools

For project virtual environments, default to enabling pip, setuptools
and wheel packages to retain existing stable behaviour to prevent
unexpected breakages caused by development environments making
assumptions of base package availability in virtual environments.

Poetry itself does not require the use of these packages and will
execute correctly within environments that do not have these packages.

This change retains the ability to manage these packages as direct
project dependency as introduced in #2826. All poetry internal
execution of pip is retaining the use of the wheel embedded within
the virtualenv package used by poetry.

In cases where a one of these reserved packages are being managed as a
project dependency, the will be treated as any other project
dependency. Executing `poetry install --remove-untracked` will not
remove any of these reserved packages. However, `poetry add pip` and
`poetry remove pip` will trigger the update and removal of `pip`
respectively.

Relates-to: #2826
Relates-to: #3916

Previously, pytest execution was influenced by poetry user
configuration. This change ensures that a new config.toml is used each
test case.

Replace updates of os.environ with explicit passing of `env` to
subprocess calls in `Env.execute()`.

Relates-to: #3199

Resolves: #3952

Throw a specific exception in the case of finding a matching
name+version, but none of the digests for a link matching the
`poetry.lock` metadata.

Fixes Issue #2422

Co-authored-by: Nicolas Simonds <nisimond@cisco.com>

In the event where we defined sources that were set as
secondary = True, we would end up with PyPI being after this source
when it should have acted as default in that case.

The main issue stems from the fact that it's not because you have
sources configured that PyPI should not be a default. Instead, PyPI
should be default if there are no sources with secondary = False and
not default if there are sources with secondary = True.

This change allows for vcs/path dependencies to be installed with
`develop=true` configured.

Resolves: #1614

* add tests for ansi and no-ansi install output

* add tests for Env.run error handling

* add tests for pip_install error handling

* encapsulate pip installation to handle interrupts

This reverts commit cd8ac0d2.

`python get-poetry.py --version 0.12.34` should exit non-zero.

This apparently regressed in 23667d28 [1].

1: https://github.com/python-poetry/poetry/commit/23667d28a96cdf62a83e944ac977e22d3ced7590#diff-952871ed95a893e0348aa1269bf15e689d18756657cfec5c7316d05e55eb6dc6R302

This change makes readme formant configurable, defaulting to markdown
when using the new command.

Resolves: #280
Closes: #1515

Co-authored-by: Arun Babu Neelicattu <arun.neelicattu@gmail.com>

Relates-to: #280

Co-authored-by: Arun Babu Neelicattu <arun.neelicattu@gmail.com>

With this change, names containing "." are treated as namespace
packages.

The following behaviour is now expected.

- "a.b.c" creates package name "a-b-c" with directory structure
  "a/b/c"
- "a-b-c" creates package name "a-b-c" with directory structure
  "a/b/c"
- "a.b_c" creates package name "a-b-c" with directory structure
  "a/b_c"
- "a_b_c" creates package name "a-b-c" with directory structure
  "a_b_c"

- remove unnecessary template duplication
- stop generating default test case (this is out of scope for poetry)
- stop generating content for package `__init__.py`
- simplify inheritance to only require base directory overrides
- remove "StandardLayout" (replaced with `Layout`)
- support handling namespace package names given in the form "a.b.c"
- specify include packages by default (be explicit)

This change is in preparation for the removal of the old bootstrap
method in favour of the new `install-poetry` script. Releases no
longer require platform specific build artifacts.

This change replaces various cases in which installed distribution and
file look-ups used path searches with importlib.metadata backed
look-ups.

This fixes issues with `dist-info` lookup for PEP610 implementation as
well as `.pth` file look-up and `dist-info` removal.

* tests: add case for transitive markers propagation

Relates-to: #3878

* deps: update poetry-core

Relates-to: #3878

* env: ignore warnings when executing python scripts

When executing python scripts with an intent to deserialise via
`json.loads` we need to ensure we ignore warnings. This is required
because, warnings can cause a `JSONDecodeError`.

Resolves: #3897

* ci: use current source if experimental

text taken from https://github.com/python-poetry/poetry/releases/tag/1.1.5