With recent setuptools, calling `python setup.py sdist` to create an
archive for zc.recipe.egg creates a zc_recipe_egg-xyz.zip instead of
a zc.recipe.egg-xyz.zip. This is called during test setup to prepare
a local package index, as the tests prevent access to PyPI. The name
change leads the index to find an entry for zc-recipe-egg instead of
zc.recipe.egg (as normalization replaces _ with -), which causes the
tests to fail to find a distribution for zc.recipe.egg.

INFO logs from setuptools which were previously not emitted because
setuptool's ad-hoc legacy logger defaulted to WARNING and above may
now be emitted because setuptools now logs to the root logger, thus
the global root logger's level configuration applied.

This caused undesired 'root: <some setuptools info>' messages to be
emitted and caused many tests to fail due to unexpected outputs.

See merge request nexedi/slapos.buildout!30

When specifying an alternate URL as fallback, the main URL is always
used for both downloading & uploading from/to networkcache.

If slapos.libnetworkcache is importable, install it in bootstrap and
in buildout upgrade - the places where bin/buildout is (re)generated
- as though it were a dependency of zc.buildout.

This is a hack to propagate libnetworkcache as a soft dependency.

Like for URL that contain credentials, we still skip auth challenge
because it's faster and:
- we only support one auth scheme (basic)
- netrc provides no way to specify realms, which seem anyway to be
  less and less used (https://stackoverflow.com/q/69303610 reports
  that recent browsers don't display them anymore)

See merge request nexedi/slapos.buildout!25

This retries with the alternate URL in case of HTTPError with the main
one.

Used by slapos.recipe.build:download* and slapos.recipe.cmmi recipes.

- Py3: stop using legacy API of urllib.request and
       fix download of http(s) URLs containing user:passwd@
- Py2: avoid OOM when downloading huge files

This is implemented as a method in case we want to make it configurable
via [buildout].

An optimization is to avoid temporary file when possible: a rename
(or hard link) is not always possible (different mount points).

Another one is to not check md5sum twice when using cache file.

Fall-back mode is ignored if an MD5 checksum is given.

In case of checksum mismatch for a cached path, remove it and
download again, mainly to cover the following cases:
- the url content changes and the user updates the checksum
- buildout killed while downloading directly to cache
  (see above optimization)
- shutil.copyfile is interrupted

We want two identical sections at different URL to be able to produce
same signature. This feature is useful for slapos.recipe.cmmi's
shared parts.

This commit may fixup "Support ${:_profile_base_location_}." but is
purposefuly kept separate because it concerns parts signatures which
are an orthogonal feature.

When there is no pinned version for zc.buildout itself, buildout
adds a ">=<current-version>" requirement to prevent accidental
downgrading. If the current version has a local version label,
this produced an invalid version specifier. To fix this, only
the public part of the current version is used.

Use a special .pydistutils.cfg in a temporary HOME directory for
the duration of the pip wheel run to prevent build dependencies
specified in a setup_requires from being installed on the fly
without respecting pinned versions.

By default pip installs build dependencies (e.g. setuptools, poetry)
in a temporary folder and temporarily adds it to sys.path in order
to proceed to build the distribution. But we want all distributions
to be installed with buildout and respect pinned versions, so we aim
to prevent pip from installing build dependencies.

Instead, we will install the build dependencies first and pass them
explicitly to zc.recipe.egg via the setup-eggs option.

This commit prevents pip from installing the build dependencies listed
by the `build-system.requires` key in the pyproject.toml file.

It may prevent pip from installing PEP 517 dynamic build dependencies
or setuptools' setup_requires dependencies.
See https://peps.python.org/pep-0517/#get-requires-for-build-wheel

While invoke setup.py certain eggs (like scikit-learn) launch
cetain custom builds (for cython) using subprocess and sys.executable.

This commit aims to preserve the sys.path over the runs, even if an
egg is using subprocess with the same python to build a component of
the egg.

Now specified patches are automatically applied on required eggs as well.

- Support on the fly patches in zc.recipe.egg by ``EGGNAME-patches``,
  ``EGGNAME-patch-options``, ``EGGNAME-patch-binary`` (or
  ``patch-binary``) and ``EGGNAME-patch-revision`` options.

- Support on the fly patches in zc.recipe.egg:custom by ``patches``,
  ``patch-options``, ``patch-binary`` and ``patch-revision`` options.
  (options ``EGGNAME-*`` are also supported as well).

Currently only zc.recipe.egg:custom supports setting environment
variables, and zc.recipe.egg:develop does not.

My motivation for allowing setting environment in :develop is
wendelin.core

    https://lab.nexedi.cn/nexedi/slapos/blob/b5faab3b/component/wendelin.core/buildout.cfg

There we have [wendelin.core] part which installs released egg from
pypi, and [wendelin.core-dev] part which installs wendelin.core from
its latest git version via zc.recipe.egg:develop .

The problem is, wendelin.core for setup.py to work, needs git available,
and with slapos we usually don't have git available on base system, so
we build it by our own and do something like

    [wendelin.core-dev]
    recipe = zc.recipe.egg:develop
    environment = wendelin.core-dev-env

    [wendelin.core-dev-env]
    # wendelin.core-dev needs git to build
    PATH = ${git:location}/bin:%(PATH)s

and the problem is environment does not currently work for
zc.recipe.egg:develop, and thus git is not found -> build fails.

~~~~

In order to support environment in :develop, we just move environment
setting/restoring bits from Custom to Base, and provide Base.install() which
uses this bits. Custom & Develop .install() becomes ._install() which gets
hooked into Base.install() .

I've tested the patch only manually, because currently automated tests are
broken in a lot of places for slapos.buildout and zc.recipe.egg .

/cc @kazuhiko, @Tyagov

Before this, sys.exit(1) was called to terminate the program directly.

Now that we use `pip wheel` + `Wheel.install_as_egg` to produce
genuine eggs, we don't need to workaround the fact that we have
not-actually-egg `.egg` bundles anymore.

If we still do need to allow for non-eggs being installed in `~/.eggs`,
via extensions or others, we should revert this.
See https://github.com/buildout/buildout/pull/352

Needed for pip wheel + setuptools.wheel.Wheel.install_as_egg.

`pip install <package>` produces a `<package-name>` package folder
and a `<package-name>.dist-info` metadata folder, which is another
format than eggs. Then buildout bundles both folders into a parent
folder `<package.egg>` and tries to act as though it were an egg.

Instead, use `pip wheel` to produce a wheel - which `pip install`
does internally anyway - and `setuptools.Wheel.install_as_egg` to
produce a genuine egg.

This is much cleaner: it consistently produces genuine eggs instead
of sometimes true eggs, sometimes `.dist-info` bundles depending on
whether `pip install` is called or the package was installed from a
`.whl` or `.egg` archive directly.

The only downside it this requires setuptools >= 38.2.3.

To be dropped once all buildout in the wild are able to upgrade to a
version that supports new names in expression of conditional sections
(see previous commit).

Adding new names for expression is currently not possible because
buildout aborts before it tries to upgrade (in-place or bootstrap).

For example, existing values were not enough to distinguish
'arm-linux-gnueabi' from 'arm-linux-gnueabihf'.

The 'multiarch' value is the output of

  $CC -dumpmachine

where CC defaults to 'gcc'.

See also https://wiki.debian.org/Multiarch/Tuples

(changed option or missing path)

Sometimes, most parts are reinstalled for a reason that the user
didn't think about and it can take time to understand why.
Explaining for all parts would be too verbose and useless because
many are reinstalled just because their dependencies changed.

Egg is installed from wheel when the requested version ends with :whl