Restore ability to set compile cache with env var PIP_TOOLS_CACHE_DIR

[AndydeCleyre]

Fixes bug introduced in #1238 and exposed by #1357

#1238's intent was to remove unnecessary environment variable handling that pip was taking care of. This pip-tools environment variable was an accidental casualty. This became apparent when parallel tests proved unstable, due to a shared cache path, while we already have an autouse fixture to isolate them (using PIP_TOOLS_CACHE_DIR env var).

Changelog-friendly one-liner: Restore ability to set compile cache with env var PIP_TOOLS_CACHE_DIR

Contributor checklist

• Provided the tests for the changes. -- I expect existing tests become stable again
• Gave a clear one-line description in the PR (that the maintainers can add to CHANGELOG.md on release).
• Assign the PR to an existing or new milestone for the target version (following Semantic Versioning).

[codecov]

Codecov Report

Merging #1368 (0b6efed) into master (1a399a6) will not change coverage.
The diff coverage is n/a.

❗ Current head 0b6efed differs from pull request most recent head 6986bd3. Consider uploading reports for the commit 6986bd3 to get more accurate results

@@           Coverage Diff           @@
##           master    #1368   +/-   ##
=======================================
  Coverage   99.65%   99.65%           
=======================================
  Files          33       33           
  Lines        2940     2940           
  Branches      308      308           
=======================================
  Hits         2930     2930           
  Misses          5        5           
  Partials        5        5           

Impacted Files	Coverage Δ
piptools/scripts/compile.py	100.00% <ø> (ø)

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[atugushev]

Nice catch! Looks like it was removed accidentally.

[ruro]

@atugushev Sorry to bother you. I see, that you added this to the version 6.1.0 milestone. Do you have any rough ETA on when will 6.1.0 get released? If you don't have an ETA, or if it's not very soon, do you think you could quickly backport this and release it as a 6.0.2 update or something? Thanks!

[atugushev]

Hello @ruro! Thanks for pinging.

Do you have any rough ETA on when will 6.1.0 get released?

We are waiting for #1363 to be merged. It's in the review process for now. Unfortunately no ETA.

If you don't have an ETA, or if it's not very soon, do you think you could quickly backport this and release it as a 6.0.2 update or something?

It would take some effort, we haven't done backports before. I'd prefer to wait for 6.1.0 instead.

[webknjaz]

I have a GitHub App for easier backports (when they apply cleanly) but this would probably require supporting multiple release streams and an extra RM to handle release tasks.

[ruro]

No problems, if you don't have a simple way to do a backport, then I'll just wait for 1363/6.1.0. Thanks.

[atugushev]

pip-tools v6.1.0 is released 🚀