feat: add flake.nix for Nix-based installation

[shunsock]

Hi! Thank you for maintaining eitango 🙏

This PR adds a flake.nix so that eitango can be installed and run via the Nix package manager.

Summary

• Add flake.nix with buildGoModule package definition for eitango
• Enable installation via nix profile install github:harumiWeb/eitango or one-off execution via nix run github:harumiWeb/eitango
• Include a devShell with Go, gopls, and golangci-lint for contributors

Usage

# Install
nix profile install github:harumiWeb/eitango

# Run without installing
nix run github:harumiWeb/eitango

# Enter dev environment
nix develop github:harumiWeb/eitango

Test plan

• nix build .#eitango succeeds
• ./result/bin/eitango version outputs correct version info
• nix flake check passes

Please let me know if there's anything you'd like me to adjust. Happy to iterate on this!

🤖 Generated with Claude Code

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Summary by CodeRabbit

• Chores
  • Added Nix flake configuration to improve build and distribution across multiple systems, including enhanced development environment setup with Go tooling.

[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: 77c7c73f-1f3c-4993-a029-6745265aaa79

📥 Commits

Reviewing files that changed from the base of the PR and between 87e99f3 and 676240e.

📒 Files selected for processing (1)

• flake.nix

✅ Files skipped from review due to trivial changes (1)

• flake.nix

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📝 Walkthrough

Walkthrough

Adds a new flake.nix Nix flake that builds and packages the eitango Go CLI per default Nix systems, embeds version/commit/date metadata into the binary, pins vendor dependencies, and provides a developer shell with Go tooling.

Changes

Cohort / File(s)	Summary
Nix Flake Configuration flake.nix	Adds a Nix flake using nixpkgs and flake-utils, generates per-system packages.eitango via pkgs.buildGoModule (CGO disabled, cmd/eitango only), embeds main.version/main.commit/main.date via ldflags, pins vendor deps with vendorHash, exposes packages.default and devShells.default (includes go, gopls, golangci-lint).

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~2 minutes

Poem

🐇
A flake I stitched with tiny paws,
Go bits bundled without a cause,
Version tucked into every byte,
Dev tools ready, build delight —
Hop, compile, and sleep tonight.

🚥 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 accurately describes the main change: adding a flake.nix file to enable Nix-based installation of the eitango Go CLI.
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 unit tests (beta)

• Create PR with unit tests

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[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

Results:
0 new issues

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[shunsock]

Thanks for the review, @coderabbitai!

Build date (line 39): Good catch! Fixed in 07e33bc — now using self.lastModifiedDate so eitango version shows a meaningful build date.

Homepage (line 44): This is intentional. harumiWeb/eitango is the upstream repository where this PR is submitted, and the Go module path is github.com/harumiWeb/eitango. The homepage should point to the canonical upstream location, not the fork.

[coderabbitai]

Tip

For best results, initiate chat on the files or code changes.

@shunsock: Thanks for the update!

• Build date: The fix using self.lastModifiedDate looks great — that will give a meaningful, reproducible timestamp for eitango version.
• Homepage: Understood, that makes perfect sense. Since the PR targets harumiWeb/eitango as the upstream and the Go module path is github.com/harumiWeb/eitango, pointing the homepage there is the correct canonical choice. My concern was misplaced — apologies for the noise!

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✏️ Learnings added

Learnt from: shunsock
URL: https://github.com/harumiWeb/eitango/pull/55

Timestamp: 2026-04-14T15:54:31.010Z
Learning: In the `flake.nix` of the `eitango` project (Go CLI, repository `harumiWeb/eitango`), the `meta.homepage` is intentionally set to `https://github.com/harumiWeb/eitango` (the upstream/canonical repo) rather than any fork. The Go module path is also `github.com/harumiWeb/eitango`. Do not flag this as incorrect in future reviews.

Note: Learnings are effective only in the context of similar code segments. To apply general coding guidelines, please configure review instructions. You can manage existing learnings in the app.

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

View in Devin Review to see 2 additional findings.

[harumiWeb]

@shunsock コントリビューションありがとうございます！
Nix flakeまだ使いこなせてないので非常に参考になります🙏
マージします。