🐛 fix(pip): invalidate install cache on resolution env var changes#3921
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rahuldevikar merged 7 commits intoApr 9, 2026
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When a user changes a resolution-affecting env var via setenv (e.g. PIP_INDEX_URL), tox previously skipped reinstalling because the requirements list was unchanged. The cache key only tracked options, requirements, constraints, and constraint_options — not the environment variables that control where or how packages are resolved. Adds _install_env_vars() to Pip, returning a filtered dict of known resolution-affecting PIP_* vars from the resolved environment. This dict is included in both the _install_requirement_file and _install_list_of_deps cache keys. Subclasses (e.g. tox-uv's UvInstaller) can override this method to include their own installer-specific vars. Not all PIP_* vars are included — only those that affect which package versions get selected (index, find-links, pre-release, constraints, require-hashes, trusted-host). Cosmetic and performance vars like PIP_TIMEOUT or PIP_VERBOSE are excluded to avoid spurious reinstalls. Fixes tox-dev#3917
for more information, see https://pre-commit.ci
…esolution vars" This reverts commit 35f1f8d.
rahuldevikar
approved these changes
Apr 9, 2026
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Setting a resolution-affecting env var via
set_env(e.g.PIP_INDEX_URL,PIP_EXTRA_INDEX_URL) had no effect on an already-cached tox environment. The install cache key tracked requirements, constraints, install options, and constraint options — but not the environment variables that control where or how pip resolves packages. A user who switched index URLs between runs would silently get stale packages from the previous cache. Reported in #3917, originally surfaced through tox-uv whereUV_EXCLUDE_NEWERinsetenvwas ignored after the first run (tox-uv side: tox-dev/tox-uv#325).The fix adds an overridable
_install_env_vars()method toPipthat returns a filtered dict of known resolution-affectingPIP_*variables from the resolved environment. This dict is folded into the cache key for both thedeps-style and list-of-deps install paths. Only vars that genuinely affect which versions get selected are included; cosmetic ones likePIP_TIMEOUTorPIP_VERBOSEare excluded to avoid spurious reinstalls. 🐛 The method is intentionally overridable so that installer plugins (e.g. tox-uv) can extend it with their own resolution-affecting vars.On the first run after upgrading, existing environments will see a one-time reinstall as the cache gains the new
"env"key. The_install_list_of_depscache format changes from a bare list to a dict; old-format caches are handled gracefully by treating a non-dictoldvalue as the requirements list directly.