…info

Changes:

- Deprecate the --egg-base parameter for dist_info and add --output-dir as
  replacement

  (Since the egg format is mostly deprecated, it is nice to move away from
  this nomenclature...)

Avoid using the editables dependency
  - The current implementation is using it to simply place .pth file
    pointing to the project directory anyway...
  - Adding a dependency for creating a file with a single line is a bit
    overkill.

Avoid importing pkg_resources directly
- Setuptools wants to move away from pkg_resources

Replace custom wheel build with re-use of bdist_wheel
  - pro: avoid re-implementing the archiving logic and make sure it is
    compatible with the same archive format used by the final wheels.
  - con: the API of wheel is not exactly stable or exported as public.

This change is heavily inspired by the existing develop command

- Use namespaces.Installer to ensure legacy namespaces are handled.

- Improve the skeleton that would allow the separation between different
  editable strategies
- Extract strategy for static .pth files
- Recognise the static .pth file as the primary strategy for src-layout
  packages in a "non"-strict scenario

- Move test_editable_prefix from test_develop to test_editable_install
- Add more tests for editable install focusing on packages using
  namespaces (legacy or PEP 420)

- Add improvements and small fixes for the static .pth file strategy
- Add initial implementation of an editable strategy based on
  MetaPathFinder but just for the top-level packages/modules
  - The idea here is to create a "loose/lax" mechanism that is able to
    handle the complex mapping mechanisms supported by setuptools (via
    package_dir) while still allowing new modules and files to be added to
    existing packages.

This workaround can be reverted when issue 3261 is fixed.

- Add implementation of editable strategy based on a link tree
  - This is the `strict` implementation.
  - Only files are linked, not directories.
    - This approach makes it possible to use harlinks when softlinks are not
      available (e.g. Windows)
    - It also guarantees files that would not be part of the final wheel are
      not available in the editable install.
- Add non-editable files to the produced wheel wheel (e.g. `headers`,
  `scripts`, `data`)

According to the PEP 420, namespace packages need to gracefully handle
later additions to path.

- Use a `PathEntryFinder` + an arbitrary placeholder entry on `sys.path`
  to force `PathFinder` to create a namespace spec.
  - Since `_NamespacePath` and `_NamespaceLoader` are private classes (or
    just documented for comparison purposes), there is no other way to
    implement this behaviour directly [^1].

[^1]: Reimplementing _NamespacePath + a custom logic to maintain
      namespace portions don't have a corresponding path entry also
      seems to have the same end result.

It requires changes in other parts of the build system/commands to be
able to be used.

`--build-option` should be used as a escape hatch to pass command
specific options, while `--global-option` can be used to pass flags like
`--quiet` or `--verbose`.

During a PEP 517 build, this directory can later be passed to
``build_py`` via the ``existing_egg_info_dir attribute``
(which in turn avoids re-running ``egg_info`` to create a manifest).

PEP 517 does not care if other directories/files are left behind in the
`metadata_directory`, as long as a `.dist_info` directory is produced at
the root. We can leave the `.egg-info` directory behind, so this way
we don't have to run it again when listing files from `build_py`.

…e build (#3398)

Improve chances that symlinks are tested directly on the relevant file
system (some machines might have multiple disks with different link
support).

…utodoc (#3429)

This is a test fix to prevent this test case for breaking test
isolation.

This is only a transitional measure that can be temporarily used by
users to help them to adapt to the PEP 660 implementation.

In this commit the argument for the `editable_wheel` command is changed
from the flag form `--strict` to `--mode=strict`.

The terms being used are: lenient, strict and compat.

Add a temporary compat mode that will try (best effort) to emulate the
same "static .pth" file produced by python setup.py develop.

This was originally suggested in
https://discuss.python.org/t/help-testing-pep-660-support-in-setuptools/16904

Mention:

- compat mode
- limitations in terms of accessing files outside of the package
  directory.
- limitations in terms of __file__ and __path__ exact values.
  implementation mechanisms