chore: remove flake-parts dependency

[ryoppippi]

Simplify flake.nix by removing flake-parts and using plain Nix. The project only defines a single devShell, which doesn't require the complexity of flake-parts.

Multi-system support is achieved with a simple forAllSystems helper using nixpkgs.lib.genAttrs. This reduces dependencies and makes the flake more straightforward.

Summary by CodeRabbit

• Chores
  • Simplified development environment configuration structure to improve consistency and maintainability across supported platforms.

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[coderabbitai]

📝 Walkthrough

Walkthrough

This PR refactors flake.nix by removing the flake-parts dependency and replacing the complex mkFlake outputs structure with a simplified declarative approach. A custom forAllSystems helper function is introduced to generate per-system devShells across the four target platforms.

Changes

Cohort / File(s)	Summary
Flake structure refactor flake.nix	Removed flake-parts dependency and replaced flake-parts.lib.mkFlake with a flat declarative outputs block. Introduced top-level let bindings containing systems array and forAllSystems generator function to replace the perSystem pattern. Per-system devShells.default now constructed via forAllSystems helper instead of nested function composition.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related PRs

• chore(nix): migrate from flake-utils to flake-parts #753: Directly modifies flake.nix outputs-level structure and per-system devShells handling related to flake-parts/mkFlake pattern.
• build: migrate CI/CD to Nix-based development environment #747: Updates flake.nix devShell and outputs configuration, though with a different dependency approach.

Poem

A rabbit hops through Nix with glee,
Removes the parts that needn't be,
With forAllSystems, clean and bright,
Four systems shine—a simpler sight! 🐰✨

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The pull request title 'chore: remove flake-parts dependency' directly and accurately summarizes the main change: removing the flake-parts dependency from flake.nix.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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📜 Recent review details

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Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 232d6b9 and e0ee783.

⛔ Files ignored due to path filters (1)

• flake.lock is excluded by !**/*.lock

📒 Files selected for processing (1)

• flake.nix

⏰ 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). (1)

• GitHub Check: Workers Builds: ccusage-guide

🔇 Additional comments (3)

flake.nix (3)

4-4: LGTM: Simplified inputs declaration.

The direct field assignment is cleaner for a single input and successfully removes the flake-parts dependency.

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6-10: LGTM: Well-implemented forAllSystems helper.

The custom forAllSystems helper correctly uses nixpkgs.lib.genAttrs to generate per-system outputs. The implementation f nixpkgs.legacyPackages.${system} properly passes the package set for each system, which is the standard approach for simplified flakes.

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11-33: LGTM: Correct devShells structure and successful refactoring.

The devShells output correctly uses the forAllSystems helper to generate the required devShells.<system>.default structure. The refactoring successfully removes flake-parts while maintaining equivalent functionality with a more straightforward implementation. Well done!

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commit: e0ee783