chore: add nix flake for development environment

[yimsk]

Summary

• Add flake.nix for Nix-based development environment
• Includes Go 1.25, go-task, golangci-lint
• Run nix develop to enter the environment

[claude]

PR Review: Nix Flake for Development Environment

Thank you for adding Nix support to the project! This is a useful addition for developers who prefer Nix-based workflows. Here's my comprehensive review:

Code Quality & Best Practices

Strengths:

• Clean, minimal flake configuration following standard Nix patterns
• Proper use of flake-utils for multi-platform support
• Uses nixos-unstable channel which is appropriate for dev environments
• Helpful shell hook that displays the Go version on entry

Suggestions:

1. Go version specificity (flake.nix:15)

   • The flake uses go_1_25 which will track the latest 1.25.x patch version from nixpkgs
   • The project's go.mod specifies go 1.25.4 explicitly
   • This is actually fine as Nix will provide a compatible 1.25.x version, but be aware that the exact patch version may differ from nixpkgs' availability

2. Missing development tools

   • The flake includes the essential tools (Go, Task, golangci-lint) ✓
   • Consider adding other common dev tools if used in the project:
     • git (if not assumed to be in the user's environment)
     • gh (GitHub CLI - used in some workflows)
     • docker (if developers use LocalStack tasks from Taskfile.yml)

3. Shell hook enhancement (flake.nix:20-22)

   • The current hook is helpful but could be more informative

4. golangci-lint version alignment

   • The CI workflow (.github/workflows/ci.yml:37) uses golangci-lint v2.8.0
   • Nix's pkgs.golangci-lint will use whatever version is in nixpkgs-unstable
   • Consider documenting the version difference

Potential Issues

Minor:

1. No .envrc file - If using direnv with Nix, developers need to manually create .envrc with use flake. Consider adding this file or documenting it in README.md

2. Documentation gap - The main README.md's Development section (lines 119-133) doesn't mention the Nix option. Should add a section about Nix setup

Performance Considerations

• Build times: First-time nix develop will download/build Go, Task, and golangci-lint. Subsequent runs use Nix cache ✓
• Disk usage: Nix store will contain these packages, but they're shared across all Nix projects on the system ✓
• No performance concerns identified

Security Concerns

Good practices observed:

• Uses official nixpkgs repository (NixOS/nixpkgs) ✓
• Flake lock file pins exact commits with hashes ✓
• No arbitrary code execution in shell hooks ✓

Considerations:

1. Dependency verification - The flake.lock pins dependencies with SHA256 hashes, which is excellent for reproducibility
2. Update mechanism - Document how to update the flake (nix flake update) when security updates are needed
3. nixpkgs-unstable channel - While appropriate for dev environments, it has less security vetting than stable releases. This is acceptable for development but worth noting.

Test Coverage

Observations:

• This PR doesn't require tests as it only adds development environment configuration ✓
• The existing CI workflow doesn't use Nix, so no CI integration needed
• Consider adding a note in the PR description or commit message about testing

Additional Recommendations

1. README update - Update the Development section to mention Nix as an option alongside the existing instructions.

Summary

This is a solid, well-structured addition that will benefit Nix users. The code quality is good, and there are no blocking issues. The main improvements would be:

1. Documentation in README.md
2. Optional: Enhanced shell hook with more info
3. Optional: Version alignment consideration with CI's golangci-lint

Recommendation: Approve with minor suggestions ✅

The flake is functional and follows Nix best practices. The suggestions above are enhancements rather than required changes. Great work!