Deprecate `--no-binary` disabling the wheel cache

[sbidoul]

Currently, --no-binary disables reading the cache of locally built wheels.

The wheel cache is however populated in some cases (such as when using pip wheel --no-binary or pip install --no-binary for projects with a pyproject.toml.

We want --no-binary to mean only one thing, namely "don't download wheels".

So we deprecate this behaviour and add a no-binary-enable-wheel-cache feature flag that will become the default in the future.

The recommended alternative is to use --no-cache or separate cache directories using --cache-dir.

[cuhe-la]

hi @sbidoul ,

DEPRECATION: --no-binary currently disables reading from the cache of locally built wheels. In the future --no-binary will not influence the wheel cache.

It sounds like we deprecate --no-binary completely. Can we add a sentence to deprecation message about this part:

We want --no-binary to mean only one thing, namely "don't download wheels".

[mid-kid]

Piping in to say thanks for this change. I frequently work in environments where prebuilt wheels don't satisfy me, and the recent PEP5something changes had made the installation of various pip packages take ages between various reinstalls of the same set of wheels. This helps a lot.