bbolt-cli-package

Packages

Package one CLI out of a larger Go repository with buildGoModule, instead of building every command the upstream module ships.

Problem

Many Go projects are primarily libraries but also ship one or more commands under cmd/. etcd-io/bbolt is the embedded BoltDB key/value store used by countless Go services, and it happens to include a handy bbolt CLI for inspecting and surgically editing those .db files on disk.

If you point buildGoModule at such a repo with no further hints, it will try to build all main packages it finds — pulling in commands you do not want, extra build time, and sometimes extra dependencies. You wanted one tool.

Key insight / trap

Two lines do the work:

subPackages = [ "cmd/bbolt" ];   # build only this one command
ldflags     = [ "-s" "-w" ];     # strip symbol table + DWARF debug info

• subPackages is the important one. It restricts the build to the given import paths (relative to the module root, i.e. the directory with go.mod). With it, buildGoModule compiles and installs exactly cmd/bbolt and nothing else. Without it, every package main in the tree becomes an output binary.
• ldflags = [ "-s" "-w" ] is the standard Go binary-slimming pair: -s drops the symbol table, -w drops DWARF debug info. Useful for an ops tool you just want to drop on a box.
• Set mainProgram in meta so lib.getExe / nix run resolve to bbolt even though pname is bbolt-cli.

Trap when adapting to another repo: vendorHash must match the vendored dependency set. Start with lib.fakeHash, build once, and paste the hash Nix reports. Same for the src hash.

Usage

# In an overlay or flake:
final: prev: {
  bbolt-cli = prev.callPackage ./packages/bbolt-cli-package { };
}

or directly:

pkgs.callPackage ./packages/bbolt-cli-package { }

Then bbolt is on PATH (add the package to environment.systemPackages, home.packages, or a nix shell).

Adapting to a different tool

To extract a different command from a different repo, change four things:

1. src (owner / repo / rev / hash),
2. vendorHash,
3. subPackages to the cmd/<name> path you actually want,
4. mainProgram / meta to match.

Everything else — the subPackages + ldflags pattern — carries over unchanged.

Source

packages/bbolt-cli-package/default.nix

# Extract ONE command from a multi-command Go module.
#
# etcd-io/bbolt is a library repo that also ships several commands under cmd/.
# We only want the `bbolt` CLI (inspect/edit BoltDB files), not the whole tree.
#
# The reusable trick: `subPackages = [ "cmd/bbolt" ]` tells buildGoModule to
# compile and install exactly that one package instead of every main package in
# the module. `ldflags = [ "-s" "-w" ]` strips the symbol table and DWARF debug
# info from the resulting binary.
#
# Build with, e.g.:
#   pkgs.callPackage ./default.nix { }
{
  lib,
  buildGoModule,
  fetchFromGitHub,
}:
buildGoModule rec {
  pname = "bbolt-cli";
  version = "1.4.3";

  src = fetchFromGitHub {
    owner = "etcd-io";
    repo = "bbolt";
    rev = "v${version}";
    # nix-prefetch or the first failing build prints the correct hash.
    hash = "sha256-awBkr2ObRxPQkMlfVFZxEbQ9JQJsFrJvSBHtqP4Hb3I=";
  };

  # Hash of the vendored Go dependencies. Set to lib.fakeHash on first build,
  # then paste the value Nix reports.
  vendorHash = "sha256-TzVmAMrNrNkFE9jQ+SILJXvbhBK1WenNPqA0FfuDU+M=";

  # THE KEY LINE: build only cmd/bbolt, not every command in the repo.
  # Paths are relative to the module root (where go.mod lives).
  subPackages = [ "cmd/bbolt" ];

  # -s strips the symbol table, -w drops DWARF debug info: smaller binary.
  ldflags = [
    "-s"
    "-w"
  ];

  meta = {
    description = "BoltDB CLI tool for inspecting and manipulating bbolt databases";
    homepage = "https://github.com/etcd-io/bbolt";
    license = lib.licenses.mit;
    mainProgram = "bbolt";
  };
}