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

maintainers/maintainer-list.nix

@@ -6760,6 +6760,12 @@
     githubId = 767083;
     name = "Derek Guenther";
   };
+  dhashs = {
+    email = "me@dha.sh";
+    github = "DhashS";
+    githubId = 4737200;
+    name = "Dhash Shrivathsa";
+  };
   dhkl = {
     email = "david@davidslab.com";
     github = "dhl";

nixos/doc/manual/redirects.json

@@ -1710,6 +1710,9 @@
   "module-security-acme-reload-dependencies": [
     "index.html#module-security-acme-reload-dependencies"
   ],
+  "module-programs-bazelisk": [
+    "index.html#module-programs-bazelisk"
+  ],
   "module-programs-zsh-ohmyzsh": [
     "index.html#module-programs-zsh-ohmyzsh"
   ],

nixos/modules/module-list.nix

@@ -180,6 +180,7 @@
   ./programs/bash/undistract-me.nix
   ./programs/bat.nix
   ./programs/bazecor.nix
+  ./programs/bazelisk.nix
   ./programs/bcc.nix
   ./programs/benchexec.nix
   ./programs/browserpass.nix

nixos/modules/programs/bazelisk.md

@@ -0,0 +1,8 @@
+# Bazelisk {#module-programs-bazelisk}
+
+The `programs.bazelisk` module installs Bazelisk as both `bazelisk` and
+`bazel`, enables envfs so unpatched Bazel binaries can resolve `/bin/bash`,
+and writes `/etc/bazel.bazelrc` with Nix store paths for common action tools.
+
+Set `programs.bazelisk.cc` and `programs.bazelisk.cxx` when a project needs C
+or C++ toolchain detection through `rules_cc`.

nixos/modules/programs/bazelisk.nix

@@ -0,0 +1,125 @@
+{
+  config,
+  lib,
+  pkgs,
+  ...
+}:
+
+let
+  cfg = config.programs.bazelisk;
+
+  # Build a PATH containing common tools that Bazel actions need.
+  defaultActionPath = lib.makeBinPath (
+    with pkgs;
+    [
+      bash
+      binutils
+      coreutils
+      findutils
+      gawk
+      gnugrep
+      gnused
+      gnutar
+      gzip
+      which
+      unzip
+    ]
+    ++ cfg.extraPackages
+  );
+
+  bazelrc = pkgs.writeText "bazel.bazelrc" ''
+    # Generated by NixOS programs.bazelisk module.
+    # NixOS needs an explicit PATH for Bazel actions since tools live in the
+    # Nix store and are not at standard FHS locations.
+    build --action_env=PATH=${defaultActionPath}
+    build --host_action_env=PATH=${defaultActionPath}
+
+    ${lib.optionalString (cfg.cc != null) ''
+      build --repo_env=CC=${cfg.cc}
+      build --action_env=CC=${cfg.cc}
+    ''}
+    ${lib.optionalString (cfg.cxx != null) ''
+      build --repo_env=CXX=${cfg.cxx}
+      build --action_env=CXX=${cfg.cxx}
+    ''}
+    ${cfg.extraBazelrc}
+  '';
+in
+{
+  options.programs.bazelisk = {
+    enable = lib.mkEnableOption ''
+      bazelisk, a version-switching launcher for Bazel.
+
+      Enabling this module installs bazelisk with a `bazel` symlink, enables
+      envfs (so unpatched Bazel binaries can find `/bin/bash`), and writes a
+      system-wide `/etc/bazel.bazelrc` that sets `--action_env=PATH` and
+      `--host_action_env=PATH` to Nix store paths for common tools.
+
+      Per-project settings (e.g. extra rustc flags, pkg-config paths) still
+      belong in `.bazelrc.user`
+    '';
+
+    package = lib.mkPackageOption pkgs "bazelisk" { };
+
+    cc = lib.mkOption {
+      type = lib.types.nullOr lib.types.str;
+      default = null;
+      example = lib.literalExpression ''"''${pkgs.clang}/bin/clang"'';
+      description = ''
+        Path to the C compiler. Set via `--repo_env=CC` and `--action_env=CC`
+        in the system bazelrc so that rules_cc toolchain detection works.
+      '';
+    };
+
+    cxx = lib.mkOption {
+      type = lib.types.nullOr lib.types.str;
+      default = null;
+      example = lib.literalExpression ''"''${pkgs.clang}/bin/clang++"'';
+      description = ''
+        Path to the C++ compiler. Set via `--repo_env=CXX` and `--action_env=CXX`
+        in the system bazelrc so that rules_cc toolchain detection works.
+      '';
+    };
+
+    extraPackages = lib.mkOption {
+      type = lib.types.listOf lib.types.package;
+      default = [ ];
+      description = ''
+        Additional packages to include in the Bazel action PATH.
+      '';
+    };
+
+    extraBazelrc = lib.mkOption {
+      type = lib.types.lines;
+      default = "";
+      description = ''
+        Extra lines appended to the system `/etc/bazel.bazelrc`.
+      '';
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    # Install bazelisk with a `bazel` symlink so it's a drop-in replacement.
+    environment.systemPackages = [
+      (pkgs.symlinkJoin {
+        name = "bazelisk-with-bazel";
+        paths = [ cfg.package ];
+        postBuild = "ln -sf $out/bin/bazelisk $out/bin/bazel";
+      })
+    ];
+
+    # envfs provides /bin/bash and /usr/bin/env for unpatched Bazel binaries.
+    services.envfs.enable = true;
+    services.envfs.extraFallbackPathCommands = ''
+      ln -s ${pkgs.bash}/bin/bash $out/bash
+    '';
+
+    # System-wide bazelrc with NixOS-compatible defaults.
+    environment.etc."bazel.bazelrc".source = bazelrc;
+  };
+
+  meta = {
+    doc = ./bazelisk.md;
+    maintainers = with lib.maintainers; [ dhashs ];
+  };
+}

nixos/tests/all-tests.nix

@@ -254,6 +254,7 @@ in
   ayatana-indicators = runTest ./ayatana-indicators.nix;
   babeld = runTest ./babeld.nix;
   bazarr = runTest ./bazarr.nix;
+  bazelisk = runTest ./bazelisk.nix;
   bcache = runTestOn [ "x86_64-linux" "aarch64-linux" ] ./bcache.nix;
   bcachefs = runTestOn [ "x86_64-linux" "aarch64-linux" ] ./bcachefs.nix;
   beanstalkd = runTest ./beanstalkd.nix;

nixos/tests/bazelisk.nix

@@ -0,0 +1,66 @@
+{
+  pkgs,
+  ...
+}:
+
+let
+  fakeBazelisk = pkgs.writeShellScriptBin "bazelisk" ''
+    echo "fake bazelisk $*"
+  '';
+
+  fakeCc = pkgs.writeShellScriptBin "bazelisk-test-cc" ''
+    exit 0
+  '';
+
+  fakeCxx = pkgs.writeShellScriptBin "bazelisk-test-cxx" ''
+    exit 0
+  '';
+
+  extraTool = pkgs.writeShellScriptBin "bazelisk-extra-tool" ''
+    echo "extra tool"
+  '';
+in
+{
+  name = "bazelisk";
+
+  nodes.machine = {
+    programs.bazelisk = {
+      enable = true;
+      package = fakeBazelisk;
+      cc = "${fakeCc}/bin/bazelisk-test-cc";
+      cxx = "${fakeCxx}/bin/bazelisk-test-cxx";
+      extraPackages = [ extraTool ];
+      extraBazelrc = ''
+        build --action_env=BAZELISK_TEST=1
+      '';
+    };
+  };
+
+  testScript = ''
+    start_all()
+
+    machine.wait_until_succeeds("mountpoint -q /usr/bin")
+    machine.wait_until_succeeds("test -e /bin/bash")
+
+    machine.succeed("test -x /run/current-system/sw/bin/bazelisk")
+    machine.succeed("test -x /run/current-system/sw/bin/bazel")
+    machine.succeed("bazel --version | grep 'fake bazelisk --version'")
+    machine.succeed("PATH= /bin/bash --version")
+
+    bazelrc = machine.succeed("cat /etc/bazel.bazelrc")
+    for expected in [
+        "build --action_env=PATH=",
+        "build --host_action_env=PATH=",
+        "${pkgs.bash}/bin",
+        "${pkgs.binutils}/bin",
+        "${pkgs.coreutils}/bin",
+        "${extraTool}/bin",
+        "build --repo_env=CC=${fakeCc}/bin/bazelisk-test-cc",
+        "build --action_env=CC=${fakeCc}/bin/bazelisk-test-cc",
+        "build --repo_env=CXX=${fakeCxx}/bin/bazelisk-test-cxx",
+        "build --action_env=CXX=${fakeCxx}/bin/bazelisk-test-cxx",
+        "build --action_env=BAZELISK_TEST=1",
+    ]:
+        assert expected in bazelrc, f"{expected!r} missing from bazelrc"
+  '';
+}

pkgs/by-name/ba/bazelisk/package.nix

@@ -2,6 +2,7 @@
   lib,
   buildGoModule,
   fetchFromGitHub,
+  nixosTests,
 }:
 
 buildGoModule (finalAttrs: {
@@ -23,11 +24,19 @@ buildGoModule (finalAttrs: {
     "-X github.com/bazelbuild/bazelisk/core.BazeliskVersion=v${finalAttrs.version}"
   ];
 
+  passthru.tests = {
+    inherit (nixosTests) bazelisk;
+  };
+
   meta = {
     description = "User-friendly launcher for Bazel";
     mainProgram = "bazelisk";
     longDescription = ''
-      BEWARE: This package does not work on NixOS.
+      A user-friendly launcher for Bazel that automatically downloads and
+      runs the correct Bazel version for a given project.
+
+      On NixOS, enable the `programs.bazelisk` module to set up envfs and
+      a system bazelrc with the correct tool paths.
     '';
     homepage = "https://github.com/bazelbuild/bazelisk";
     changelog = "https://github.com/bazelbuild/bazelisk/releases/tag/v${finalAttrs.version}";