builtins.getFlake: Handle path:<p> where p has a discarded string context

[edolstra]

Motivation

For instance, github:Mic92/sops-nix/8b89f44c2cc4581e402111d928869fe7ba9f7033 does this:

loadPrivateFlake =
  path:
  let
    flakeHash = builtins.readFile "${toString path}.narHash";
    flakePath = "path:${toString path}?narHash=${flakeHash}";
  in
  builtins.getFlake (builtins.unsafeDiscardStringContext flakePath);

This previously resulted in

error: path '/nix/store/2c8r30kz9zg8kz11ngp64ah5ya0hc011-source/dev/private/flake.nix' does not exist

when using lazy trees.

Fixes #345.

Context

Summary by CodeRabbit

• Refactor
  • Optimized path-type flake reference handling for improved resolution when sources are already present in the store.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 612d411c-fdb6-4aae-b482-1a5eb8260b33

📥 Commits

Reviewing files that changed from the base of the PR and between 6ab99ab and b3b623d.

📒 Files selected for processing (1)

• src/libflake/flake-primops.cc

---

📝 Walkthrough

Walkthrough

The getFlake primitive now special-cases path-type flake references after devirtualization. When a path flake ref resolves to a store-present path, the code derives the store path, scans the realized string context for a matching path element, constructs a concrete path, and invokes lockFlake directly with that path before returning, bypassing the original flow.

Changes

Cohort / File(s)	Summary
Path Flake Reference Handling src/libflake/flake-primops.cc	Added special-case logic in getFlake primitive to detect path-type flake refs, derive store paths, match against realized NixStringContext elements, and construct concrete paths for direct lockFlake invocation.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• builtins.getFlake fixes #337 — Modifies flake-primops.cc to devirtualize and propagate Nix string context in getFlake/flakeRefToString for proper store-path flakeRef handling.
• builtins.getFlake: Support path values #338 — Also modifies flake-primops.cc's getFlake to special-case path-style flake references with alternative lockFlake invocation path.

Suggested reviewers

• cole-h

Poem

🐰 A path through the store, once twisted and lost,
Now springs straight and true—no context cost!
The flakes align where virtues meet real,
And sops-nix can show what it's meant to reveal! ✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 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: handling path flake references with discarded string context in builtins.getFlake, which is the core fix for the reported issue.
Linked Issues check	✅ Passed	The changes directly address issue #345 by implementing special handling for 'path:' flake refs with discarded context, allowing builtins.getFlake to resolve the flake instead of failing with path-not-exist errors.
Out of Scope Changes check	✅ Passed	All changes in src/libflake/flake-primops.cc are focused solely on fixing the getFlake primitive to handle path refs with discarded context, remaining within the scope of issue #345.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch getFlake-discarded-context

---

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[github-actions]

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