Add missing temp roots

[edolstra]

Motivation

Backport of NixOS#15237 + a similar fix to AsyncPathWriter.

Context

Summary by CodeRabbit

• Bug Fixes
  • Improved cache protection mechanisms to prevent accidental garbage collection of cached inputs across store operations. Temporary root management has been added during path storage, async write operations, and derivation processing to ensure cached data persists reliably and reduces the risk of unintended data loss.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

Configuration used: defaults

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 908be63 and 618c4df.

📒 Files selected for processing (3)

• src/libfetchers/fetch-to-store.cc
• src/libstore/async-path-writer.cc
• src/libstore/derivations.cc

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📝 Walkthrough

Walkthrough

The changes add temporary root registration across three store modules to prevent accidental garbage collection. Each modification calls addTempRoot() before performing store operations on paths, ensuring cached inputs and derivations remain valid during processing.

Changes

Cohort / File(s)	Summary
Temporary Root Registration src/libfetchers/fetch-to-store.cc, src/libstore/async-path-writer.cc, src/libstore/derivations.cc	Adds addTempRoot() calls before store path operations to prevent accidental garbage collection of cached inputs and derivations.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

Hops through the store with roots held tight,
Temp anchors placed to save the night,
No garbage shall steal treasures here,
Three guards stand watch, both far and near! 🐰✨

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'Add missing temp roots' directly summarizes the main objective of the pull request, which is to add missing temporary root registrations across multiple components.

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✨ Finishing Touches

• 📝 Generate docstrings (stacked PR)
• 📝 Generate docstrings (commit on current branch)

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch add-missing-temp-roots

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[github-actions]

🚀 Deployed on https://69a1d0fe94b83265cb465bf0--determinate-nix.netlify.app

[xokdvium]

Btw I think that in this case the remote side already adds temp roots https://github.com/NixOS/nix/blob/fa1a370c6fb827883d1d34317f31f948a1f44b7b/src/libstore/local-store.cc#L1210

It's more of the pattern of isValidPath that needs to have a temp root added first.