Support .gitattributes in subdirectories

[edolstra]

Motivation

For performance, the Git backwards compatibility hack was only applied to repositories that had a .gitattributes in the root directory. However, there are real-world repos that have it in subdirectories, so drop that condition.

Context

Summary by CodeRabbit

• Bug Fixes

  • Fixed an error message so expected vs. actual hash values display in the correct order.

• Improvements

  • Simplified Git input fingerprinting to use a consistent hashing rule.
  • Broadened when updated Git export behavior applies to improve compatibility with legacy flows.

• Tests

  • Updated Git fetch test fixtures and expectations for a reorganized repository layout and new hash results.

[coderabbitai]

📝 Walkthrough

Walkthrough

Fixes an error-message hash ordering, simplifies Git input fingerprinting by removing a .gitattributes presence check, relaxes when Nix 2.19 semantics apply for Git NAR-hash handling (with a legacy fallback), and moves test fixtures into a dir/ subdirectory with updated expectations.

Changes

Cohort / File(s)	Summary
Error Message Formatting src/libexpr/paths.cc	Swaps the two hash arguments in EvalState::mountInput error output so "expected" and "got" match the template.
Fingerprinting Logic Simplification src/libfetchers/fetchers.cc	Removes .gitattributes existence branching; Git inputs now always use the store path hash for fingerprinting.
Git Semantics & NAR-hash Handling src/libfetchers/git.cc	Uses runProgram in legacy submodule path, broadens nix219Compat gating (settings.nix219Compat && !options.smudgeLfs), computes/compares narHashNew when provided regardless of .gitattributes, and falls back to legacy accessor only if legacy nar hash matches.
Test Data & Expectations tests/functional/fetchGit.sh	Moves test files and Git metadata into dir/; updates fetchTree, flake.lock expectations and NAR-hash values/messages to match new layout.

Sequence Diagram(s)

sequenceDiagram
    participant Tester
    participant Fetcher
    participant GitAccessor
    participant LegacyAccessor
    participant Store
    Tester->>Fetcher: request Git input
    Fetcher->>GitAccessor: construct accessor (nix219Compat? smudgeLfs?)
    GitAccessor->>Store: compute store path hash / narHashNew (if expected provided)
    Store-->>GitAccessor: narHashComputed
    GitAccessor->>GitAccessor: compare expectedNarHash vs narHashComputed
    alt match
        GitAccessor-->>Fetcher: return new accessor
    else mismatch
        GitAccessor->>LegacyAccessor: compute legacy nar hash
        alt legacy matches
            LegacyAccessor-->>Fetcher: return legacy accessor (fallback)
        else
            GitAccessor-->>Fetcher: return accessor with updated path/hash
        end
    end
    Fetcher-->>Tester: accessor returned

Loading

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Possibly related PRs

• Backward compatibility hack for Nix < 2.20 Git inputs using git-archive #278: Related changes to Git fetcher/accessor fingerprint and NAR-hash comparison logic, including nix219Compat gating.
• Only try to substitute input if fetching from its original location fails #202: Changes to Input::getAccessorUnchecked in src/libfetchers/fetchers.cc affecting fingerprint/substitution logic.

Suggested labels

flake-regression-test

Suggested reviewers

• grahamc
• cole-h

Poem

🐰 I hopped through hashes, neat and quick,
Swapped their places with a tiny trick.
.gitattributes? I've let it go,
Tests now nest where small carrots grow,
A twitchy nose for tidy git.

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 25.00% 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 'Support .gitattributes in subdirectories' directly and accurately summarizes the main objective: extending .gitattributes support beyond repository root to subdirectories, which is the core change across all modified files.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ 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 eelcodolstra/nix-285-support-gitattributes-in-all-directories

---

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

[github-actions]

🚀 Deployed on https://69847711d1279d3101ef2da1--determinate-nix.netlify.app

[coderabbitai]

Actionable comments posted: 0

Caution

Some comments are outside the diff and can’t be posted inline due to platform limitations.

⚠️ Outside diff range comments (1)

src/libfetchers/git.cc (1)

1000-1014: ⚠️ Potential issue | 🟡 Minor

Warn only when legacy semantics are actually used.
If expectedNarHash matches the modern hash, the code switches to the modern accessor but still logs “Using Nix 2.19 semantics…”, which is misleading.

Suggested minimal adjustment

-            warn("Using Nix 2.19 semantics to export Git repository '%s'.", input.to_string());
+            bool useLegacy = true;
             auto accessorModern = accessor;
             accessor = getLegacyGitAccessor(store, repoInfo, repoDir, rev, options);
             if (expectedNarHash) {
                 auto narHashLegacy =
                     fetchToStore2(settings, store, {accessor}, FetchMode::DryRun, input.getName()).second;
                 if (expectedNarHash != narHashLegacy) {
                     auto narHashModern =
                         fetchToStore2(settings, store, {accessorModern}, FetchMode::DryRun, input.getName()).second;
                     if (expectedNarHash == narHashModern)
-                        accessor = accessorModern;
+                        { accessor = accessorModern; useLegacy = false; }
                 }
             }
+            if (useLegacy)
+                warn("Using Nix 2.19 semantics to export Git repository '%s'.", input.to_string());