nix flake check: Remove incorrect assertion

[edolstra]

Motivation

The assumption that no unknown paths can be returned is incorrect. It can happen if a derivation has outputs that are substitutable, but that have references that cannot be substituted (i.e. an incomplete closure in the binary cache). This can easily happen with magic-nix-cache.

Context

Summary by CodeRabbit

• Refactor
  • Removed a runtime validation check to streamline the check process, allowing the application to proceed without this strict enforcement.

[coderabbitai]

Walkthrough

The change removes a runtime assertion from the flake check code path that previously validated missing.unknown was empty after computing missing derivations for drvPaths. The code now proceeds without this validation check.

Changes

Cohort / File(s)	Summary
Assertion Removal src/nix/flake.cc	Removed assertion enforcing missing.unknown to be empty after computing missing derivations

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~2 minutes

• Straightforward removal of a single assertion; focus on understanding the rationale for removing the validation and confirming no correctness implications

Suggested reviewers

• cole-h

Poem

A rabbit hops through flakes so grand,
Removing checks where none are planned,
One assertion freed, the path runs clear,
Trust the missing, have no fear! 🐰✨

Pre-merge checks and finishing touches

✅ 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 accurately describes the main change: removing an incorrect assertion from the nix flake check code, which is clearly supported by the file summary and PR objectives.

✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch fix-nix-flake-check-crash

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📜 Recent review details

Configuration used: CodeRabbit UI

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 51fa1ca and 7a77e87.

📒 Files selected for processing (1)

• src/nix/flake.cc (0 hunks)

💤 Files with no reviewable changes (1)

• src/nix/flake.cc

⏰ Context from checks skipped due to timeout of 90000ms. You can increase the timeout in your CodeRabbit configuration to a maximum of 15 minutes (900000ms). (2)

• GitHub Check: build_x86_64-linux / build
• GitHub Check: build_aarch64-darwin / build

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[github-actions]

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