feat: add environment variable to disable writing installer metadata files

[adisbladis]

Summary

This change introduces the UV_NO_INSTALLER_METADATA environment variable
as a way to opt out of the extra installer metadata files that uv is creating.

This is important to achieve reproducible builds in distribution
packaging, allowing to replace usage of
installer with uv pip install.

At the time of writing these files are:

• uv_cache.json
  Contains timestamps which are non-reproducible.
  These hashes also leak in to the RECORD file.

• direct_url.json
  Contains the path to the installed wheel.
  While not non-reproducible it's not required for distribution packaging.

• INSTALLER
  Again, not non-reproducible, but of no value in distribution packaging.

Test Plan

Automated test added.

[zanieb]

Thanks for putting up the PR!

Note to other reviewers, we briefly discussed using an environment variable for this in Discord.

I don't have strong opinions on the name, but we might want to use UV_NO_EXTRA_DIST_INFO=1 rather than UV_EXTRA_DIST_INFO=0?

Otherwise, I'm not well suited to be the primary reviewer for this. Perhaps @konstin or @charliermarsh would be interested.

[adisbladis]

I don't have strong opinions on the name, but we might want to use UV_NO_EXTRA_DIST_INFO=1 rather than UV_EXTRA_DIST_INFO=0?

It made more sense to me when writing this to think about it the other way around, but it's indeed seems more consistent with other options to use UV_NO_EXTRA_DIST_INFO=1.

[konstin]

What's the motivation for going through wheel installation for repackaging over re-zipping the wheel into the target format you are interested in?

[adisbladis]

What's the motivation for going through wheel installation for repackaging over re-zipping the wheel into the target format you are interested in?

Sorry, I don't understand the question? I'll explain my use case in more detail, hopefully we'll find some understanding.

The use case for this PR is to replace usage of installer with uv in distribution packaging scripts.
These scripts need to:

• Invoke a Python build system, such as pypa/build which takes a source tree and outputs a wheel
  • Or download a pre-built wheel
• Invoke an installer that can install said wheel into a prefix

In nixpkgs we use:

• pypa/installer to install Python wheels.
• pypa/build to build Python packages from source
• In some rare cases download pre-built wheels

For distribution packaging we want reproducible builds, meaning that the outputs produced by a packaging script should be bit-for-bit identical.
Nix comes with tooling to perform these checks: nix-build ./. -A somePackage --check.

I have implemented an alternative Python build infrastructure for Nix where I use uv.
These builds end up failing reproducibility checks because of extra dist info files.

At some point in the future I'd like to replace the nixpkgs install hook with a uv implementation too. A requisite for that is that outputs are reproducible.

[adisbladis]

Ping @charliermarsh

[charliermarsh]

I'm not super excited to maintain this but I see the value. I think we should call this "installer metadata" rather than "extra dist-info", since the latter is just a term we made up within the wheel installer crate. How's that sound?

[adisbladis]

I'm not super excited to maintain this but I see the value.

Thank you. I understand that the use case is a bit niche from a Python perspective.

I think we should call this "installer metadata" rather than "extra dist-info", since the latter is just a term we made up within the wheel installer crate. How's that sound?

Yep, that sounds much better!

[adisbladis]

Ping again @charliermarsh

[charliermarsh]

Ack, will review (and hopefully merge) soon.