go-overlay

README

go-overlay

A Nix overlay for Go development. Pure[^1], reproducible[^2], and auto-updated[^3].

[^1]: No side effects—builds depend only on declared inputs, not system state.

[^2]: Given the same inputs, builds produce byte-for-byte identical outputs. Pin a Go version today and get the exact same binary in 5 years.

[^3]: GitHub Actions monitors go.dev every 4 hours. When a new release is detected, a manifest is generated and committed automatically—no manual intervention required.

• Why it exists?
• Quick Start
• Installation
• Library Functions
• Builder Functions
• Building a Go Application
• Detecting Drift with Git Hooks
• Using with buildGoModule
• Migrating from nixpkgs
• Used by

Why it exists?

Feature	go-overlay	nixpkgs
Versions available	100+ (1.17 – latest)	2 per nixpkgs commit
New release availability	Up to 4 hours after upstream	Days to weeks
Multiple versions	Single flake input	Multiple nixpkgs pins required
Release candidates	Available	Not available
Building applications	No vendorHash required	vendorHash must be computed

[!NOTE] Older Go versions are accessible in nixpkgs by pinning historical commits, but this requires managing multiple nixpkgs inputs and finding the correct commit for each version.

Quick Start

Try Go without installing anything permanently.

Direct Execution

Run Go without any setup:

nix run github:purpleclay/go-overlay -- version
# go version go1.25.5 linux/amd64

Shell Environment

Interactive development:

nix shell github:purpleclay/go-overlay
go version
# go version go1.25.5 linux/amd64

Build Output

Create a derivation:

nix build github:purpleclay/go-overlay
./result/bin/go version
# go version go1.25.5 linux/amd64

Specific Version

Pin to a known version using the format go_<major>_<minor>_<patch>:

nix shell github:purpleclay/go-overlay#go_1_23_2
go version
# go version go1.23.2 linux/amd64

Installation

Nix Flakes

Add go-overlay to your flake inputs and apply the overlay:

{
  description = "My Go Project";

  inputs = {
    nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
    flake-utils.url = "github:numtide/flake-utils";
    go-overlay.url = "github:purpleclay/go-overlay";
  };

  outputs = { nixpkgs, go-overlay, flake-utils, ... }:
    flake-utils.lib.eachDefaultSystem (system:
      let
        pkgs = import nixpkgs {
          inherit system;
          overlays = [ go-overlay.overlays.default ];
        };
      in
      {
        devShells.default = pkgs.mkShell {
          buildInputs = [ pkgs.go-bin.latest ];
        };
      }
    );
}

nix develop
go version
# go version go1.25.5 linux/amd64

Traditional Nix (non-flake)

For users not using flakes, go-overlay can be imported directly as an overlay.

[!TIP] For reproducible builds, pin to a specific commit instead of main:

builtins.fetchTarball "https://github.com/purpleclay/go-overlay/archive/<commit-sha>.tar.gz"

Find commit SHAs here.

Option 1: Using fetchTarball

Direct import in your expression:

let
  go-overlay = import (builtins.fetchTarball
    "https://github.com/purpleclay/go-overlay/archive/main.tar.gz");

  pkgs = import <nixpkgs> {
    overlays = [ go-overlay ];
  };
in
pkgs.mkShell {
  buildInputs = [ pkgs.go-bin.latest ];
}

Option 2: User Overlays

Add to ~/.config/nixpkgs/overlays.nix:

[
  (import (builtins.fetchTarball
    "https://github.com/purpleclay/go-overlay/archive/main.tar.gz"))
]

Then use in any expression:

let
  pkgs = import <nixpkgs> {};
in
pkgs.go-bin.latest

Option 3: Nix Channels

nix-channel --add https://github.com/purpleclay/go-overlay/archive/main.tar.gz go-overlay
nix-channel --update

Then import the channel:

let
  go-overlay = import <go-overlay>;

  pkgs = import <nixpkgs> {
    overlays = [ go-overlay ];
  };
in
pkgs.go-bin.latest

Library Functions

go-bin.latest

Get the absolute latest version, including release candidates.

Use when: You want cutting-edge features and don't mind pre-release software.

go-bin.latest

go-bin.latestStable

Get the latest stable version, excluding release candidates. Recommended for production.

Use when: You need stability and don't require the latest features.

go-bin.latestStable

go-bin.versions.<version>

Pin to an exact version for complete reproducibility.

Use when: You need deterministic builds and exact version control.

go-bin.versions."1.21.4"
go-bin.versions."1.25.4"

go-bin.hasVersion <version>

Check if a specific version is available before using it.

Use when: You want to handle missing versions gracefully.

if go-bin.hasVersion "1.22.0"
then go-bin.versions."1.22.0"
else go-bin.latestStable

go-bin.isDeprecated <version>

Check if a version is deprecated (EOL) according to Go's release policy.

Go supports the current and previous minor versions. If the latest stable is 1.25.x:

go-bin.isDeprecated "1.23.4"  # true (two versions behind)
go-bin.isDeprecated "1.24.0"  # false (previous minor, supported)
go-bin.isDeprecated "1.25.0"  # false (current minor, supported)

go-bin.fromGoMod <path>

Auto-select Go version from go.mod. Uses toolchain directive if present, otherwise the latest patch of the go directive.

Use when: You want automatic version selection based on your project.

go-bin.fromGoMod ./go.mod

go-bin.fromGoModStrict <path>

Strict version matching from go.mod. No automatic patch version selection; fails if exact version is unavailable.

Use when: You need exact reproducibility and want early failure on version mismatch.

go-bin.fromGoModStrict ./go.mod

Behavior Comparison

[!NOTE] fromGoMod is flexible and forgiving—great for development. fromGoModStrict is strict and predictable—better for reproducible builds.

go.mod Declaration	fromGoMod	fromGoModStrict
go 1.21	Latest 1.21.x	Error
go 1.21.6	1.21.6	1.21.6
go 1.21 + toolchain go1.21.6	1.21.6	1.21.6

Builder Functions

go-overlay provides builder functions for Go applications using vendored dependencies. Unlike nixpkgs' buildGoModule, these work with unpatched Go binaries from go.dev and don't require computing a vendorHash.

buildGoApplication

Build a Go application using a govendor.toml manifest.

Use when: You want reproducible Go builds without the vendorHash dance.

buildGoApplication {
  pname = "my-app";
  version = "1.0.0";
  src = ./.;
  go = pkgs.go-bin.latest;
  subPackages = [ "cmd/my-app" ];
}

Option	Default	Description
pname	required	Package name
version	required	Package version
src	required	Source directory
go	required	Go derivation from go-overlay
modules	src + "/govendor.toml"	Path to govendor.toml manifest
subPackages	["."]	Packages to build (relative to src)
ldflags	[]	Linker flags
tags	[]	Build tags
CGO_ENABLED	inherited from go	Enable CGO

mkVendorEnv

Create a vendor directory with modules.txt from a parsed govendor.toml manifest. This is a lower-level function used internally by buildGoApplication.

Use when: You need custom control over the vendor directory or build process.

mkVendorEnv {
  go = pkgs.go-bin.latest;
  manifest = builtins.fromTOML (builtins.readFile ./govendor.toml);
}

Option	Default	Description
go	required	Go derivation from go-overlay
manifest	required	Parsed govendor.toml (via fromTOML)

The resulting derivation contains symlinks to each module at their import path and a modules.txt with package listings.

Building a Go Application

Step 1: Add govendor to Your Dev Shell

Add govendor to your development shell to generate vendor manifests:

# flake.nix
{
  inputs.go-overlay.url = "github:purpleclay/go-overlay";

  outputs = { self, nixpkgs, go-overlay, ... }:
    let
      pkgs = import nixpkgs {
        system = "x86_64-linux";
        overlays = [ go-overlay.overlays.default ];
      };
    in {
      devShells.default = pkgs.mkShell {
        buildInputs = [
          pkgs.go-bin.fromGoMod ./go.mod
          go-overlay.packages.${pkgs.system}.govendor
        ];
      };
    };
}

Step 2: Generate a Vendor Manifest

Run govendor to generate a govendor.toml manifest:

govendor

This creates a govendor.toml file with NAR hashes for all dependencies. Commit this file to your repository.

[!TIP] Re-run govendor whenever your dependencies change. Use govendor --check in CI to detect manifest drift, or set up a git hook to catch drift before committing.

Step 3: Create a Package Definition

Create a default.nix file to build your application:

# default.nix
{
  buildGoApplication,
  go,
}:
buildGoApplication {
  pname = "my-app";
  version = "1.0.0";
  src = ./.;
  inherit go;
  subPackages = [ "cmd/my-app" ];
  ldflags = [ "-s" "-w" ];
}

Step 4: Build Your Application

Add the package to your flake outputs:

# flake.nix
{
  packages.default = pkgs.callPackage ./default.nix {
    inherit (pkgs) buildGoApplication;
    go = pkgs.go-bin.fromGoMod ./go.mod;
  };
}

Build with:

nix build

Detecting Drift with Git Hooks

Use cachix/git-hooks.nix to automatically check for manifest drift when go.mod changes:

# flake.nix
{
  inputs = {
    nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
    go-overlay.url = "github:purpleclay/go-overlay";
    git-hooks.url = "github:cachix/git-hooks.nix";
  };

  outputs = { self, nixpkgs, go-overlay, git-hooks, ... }:
    let
      system = "x86_64-linux";
      pkgs = import nixpkgs {
        inherit system;
        overlays = [ go-overlay.overlays.default ];
      };

      pre-commit-check = git-hooks.lib.${system}.run {
        src = ./.;
        hooks = {
          govendor = {
            enable = true;
            name = "govendor";
            description = "Check if govendor.toml has drifted from go.mod";
            entry = "${go-overlay.packages.${system}.govendor}/bin/govendor --check";
            files = "(^|/)go\\.mod$";
            pass_filenames = true;
          };
        };
      };
    in {
      devShells.default = pkgs.mkShell {
        inherit (pre-commit-check) shellHook;
        buildInputs = pre-commit-check.enabledPackages;
      };
    };
}

When you modify go.mod and attempt to commit, the hook will fail if govendor.toml is out of sync:

govendor.................................................................Failed
- hook id: govendor
- exit code: 1

╭────────────┬─────────┬──────────────────────────────────────────────╮
│ GoMod File │ Status  │ Message                                      │
├────────────┼─────────┼──────────────────────────────────────────────┤
│ go.mod     │ ✗ drift │ go.mod has changed, regenerate govendor.toml │
╰────────────┴─────────┴──────────────────────────────────────────────╯

Run govendor to regenerate the manifest, then commit both files together.

Using with buildGoModule

buildGoModule defaults to nixpkgs' Go toolchain. To use go-overlay, you must override it.

[!WARNING] Simply passing go as an argument will not work because buildGoModule ignores build arguments for its Go dependency.

Override in default.nix

# default.nix
{
  pkgs,
  go,
}:
(pkgs.buildGoModule.override { inherit go; }) {
  pname = "my-app";
  version = "1.0.0";
  src = ./.;
  vendorHash = "sha256-...";
}

Override in flake.nix

# flake.nix
{
  packages.my-app = pkgs.callPackage ./default.nix {
    go = pkgs.go-bin.versions."1.22.3";
  };
}

Migrating from nixpkgs

Migrating from nixpkgs to go-overlay involves changing how Go versions are specified in your Nix expressions.

Before (nixpkgs)

# pin to minor version only
{
  buildInputs = [ pkgs.go_1_24 ];
}

After (go-overlay)

# pin to exact version
{
  buildInputs = [ pkgs.go-bin.versions."1.24.5" ];
}

Used By

• devenv - Fast, declarative, reproducible developer environments