feat: implement conflict promotion logic in requirement selection

[frostming]

Signed-off-by: Frost Ming [email protected]

Related link: pypa/pip#13859

Pull Request Checklist

• A news fragment is added in news/ describing what is new.
• Test cases added for changed code.

Describe what you have changed in this PR.

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 9970fa8dcf

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[chatgpt-codex-connector]

Count promotions only on new backtracks

This increments _conflict_counts every time narrow_requirement_selection() runs with the last backtrack_causes, but resolvelib keeps that same backtrack_causes list across subsequent successful rounds. In practice, a package that conflicted once can cross the threshold after a few unrelated pins and get added to _conflict_promoted permanently. That turns this into a “stale last conflict” heuristic instead of a “repeated conflicts” heuristic, which can reorder later rounds badly enough to hit resolve_max_rounds on otherwise-solvable dependency sets.

Useful? React with 👍 / 👎.

[frostming]

How to fix this? @codex

[chatgpt-codex-connector]

To use Codex here, create an environment for this repo.

[codecov]

Codecov Report

❌ Patch coverage is 90.62500% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.12%. Comparing base (d14eebc) to head (5681f28).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/pdm/resolver/providers.py	90.62%	1 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3751      +/-   ##
==========================================
+ Coverage   86.09%   86.12%   +0.03%     
==========================================
  Files         118      118              
  Lines       12374    12406      +32     
  Branches     2060     2071      +11     
==========================================
+ Hits        10653    10685      +32     
  Misses       1150     1150              
  Partials      571      571              

Flag	Coverage Δ
unittests	85.98% <90.62%> (+0.03%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.