nixos/bazelisk: add NixOS module; remove "does not work" warning

[DhashS]

Summary

Add a programs.bazelisk NixOS module that makes bazelisk work on NixOS, and remove the BEWARE: This package does not work on NixOS warning from the bazelisk package meta.

Motivation

Bazelisk downloads unpatched Bazel binaries that fail on NixOS because:

1. /bin/bash doesn't exist (or isn't resolvable with an empty PATH)
2. Common tools (touch, grep, etc.) aren't at FHS-standard paths
3. rules_cc toolchain detection can't find a C compiler

The existing bazel_9 nix package solves this by building Bazel from source with 6+ patches, but that locks you to a single version. Bazelisk's whole purpose is version-switching via .bazelversion, which the patched package can't support.

What the module does

programs.bazelisk.enable = true sets up three things:

1. Installs bazelisk with a bazel symlink so it's a drop-in replacement
2. Enables envfs with bash in the fallback path, so /bin/bash resolves even when Bazel strips the environment (exec env -)
3. Writes /etc/bazel.bazelrc with --action_env=PATH and --host_action_env=PATH pointing to Nix store paths for common tools (bash, coreutils, findutils, gawk, gnugrep, gnused, gnutar, gzip, which, unzip)

Optional cc/cxx options set --repo_env=CC/CXX for rules_cc toolchain detection. extraPackages and extraBazelrc allow further customization.

Example usage

programs.bazelisk = {
  enable = true;
  cc = "${pkgs.clang}/bin/clang";
  cxx = "${pkgs.clang}/bin/clang++";
};

Per-project settings (e.g. extra rustc flags, pkg-config paths) still go in .bazelrc.user.

Testing

Tested on a real-world Bazel project with Rust, TypeScript, and Swift rules — 27/27 targets building on both Bazel 9.0.1 and 9.0.2 by simply changing .bazelversion and letting bazelisk do its thing.

Note: there's a companion fix needed in bazel_env.bzl to replace touch with a bash builtin in one of its actions, but all other Bazel rules work out of the box.

Files changed

• nixos/modules/programs/bazelisk.nix — new NixOS module
• nixos/modules/module-list.nix — register the module
• pkgs/by-name/ba/bazelisk/package.nix — update meta description

This PR was vibe coded with Claude Code.