npm: add module

modules/misc/news/2025/12/2025-12-06_11-03-01.nix

@@ -0,0 +1,10 @@
+{
+  time = "2025-12-06T10:03:01+00:00";
+  condition = true;
+  message = ''
+    A new module is available: `programs.npm`
+
+    It allows you manage your npm user configuration (`.npmrc`)
+    and install a specific version of the package.
+  '';
+}

modules/programs/npm.nix

@@ -0,0 +1,74 @@
+# https://github.com/NixOS/nixpkgs/blob/master/nixos/modules/programs/npm.nix
+{
+  config,
+  lib,
+  pkgs,
+  ...
+}:
+let
+  cfg = config.programs.npm;
+
+  xdgConfigHome = lib.removePrefix config.home.homeDirectory config.xdg.configHome;
+  configFile = if config.home.preferXdgDirectories then "${xdgConfigHome}/npm/npmrc" else ".npmrc";
+
+  iniFormat = pkgs.formats.ini {
+    listsAsDuplicateKeys = true;
+  };
+
+  toNpmrc =
+    let
+      mkLine = lib.generators.mkKeyValueDefault { } "=";
+      mkLines = k: v: if lib.isList v then map (x: mkLine "${k}[]" x) v else [ (mkLine k v) ];
+    in
+    attrs: lib.concatLines (lib.concatLists (lib.mapAttrsToList mkLines attrs));
+in
+{
+  meta.maintainers = with lib.maintainers; [ mirkolenz ];
+
+  options = {
+    programs.npm = {
+      enable = lib.mkEnableOption "{command}`npm` user config";
+
+      package = lib.mkPackageOption pkgs [ "nodejs" ] {
+        example = "nodejs_24";
+        nullable = true;
+      };
+
+      settings = lib.mkOption {
+        type = lib.types.attrsOf iniFormat.lib.types.atom;
+        description = ''
+          The user-specific npm configuration.
+          See <https://docs.npmjs.com/cli/using-npm/config> and
+          <https://docs.npmjs.com/cli/configuring-npm/npmrc>
+          for more information.
+        '';
+        default = {
+          prefix = "\${HOME}/.npm";
+        };
+        example = lib.literalExpression ''
+          {
+            color = true;
+            include = [
+              "dev"
+              "prod"
+            ];
+            init-license = "MIT";
+            prefix = "''${HOME}/.npm";
+          }
+        '';
+      };
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    home = {
+      packages = lib.mkIf (cfg.package != null) [ cfg.package ];
+      file.${configFile} = lib.mkIf (cfg.settings != { }) {
+        text = toNpmrc cfg.settings;
+      };
+      sessionVariables = lib.mkIf (cfg.settings != { }) {
+        NPM_CONFIG_USERCONFIG = "${config.home.homeDirectory}/${configFile}";
+      };
+    };
+  };
+}

tests/modules/programs/npm/default.nix

@@ -0,0 +1,4 @@
+{
+  npm-example-settings = ./example-settings.nix;
+  npm-no-settings = ./no-settings.nix;
+}

tests/modules/programs/npm/example-settings.nix

@@ -0,0 +1,36 @@
+{ pkgs, ... }:
+
+{
+  programs.npm = {
+    enable = true;
+    settings = {
+      color = true;
+      include = [
+        "dev"
+        "prod"
+      ];
+      init-license = "MIT";
+      prefix = "\${HOME}/.npm";
+    };
+  };
+
+  test.stubs.nodejs = { };
+
+  nmt.script =
+    let
+      configPath = "home-files/.npmrc";
+      expectedConfig = pkgs.writeText "npmrc-expected" ''
+        color=true
+        include[]=dev
+        include[]=prod
+        init-license=MIT
+        prefix=''${HOME}/.npm
+      '';
+    in
+    ''
+      assertFileExists "${configPath}"
+      assertFileContent "${configPath}" "${expectedConfig}"
+      assertFileContains home-path/etc/profile.d/hm-session-vars.sh \
+        'export NPM_CONFIG_USERCONFIG="/home/hm-user/.npmrc"'
+    '';
+}

tests/modules/programs/npm/no-settings.nix

@@ -0,0 +1,17 @@
+{ ... }:
+
+{
+  programs.npm = {
+    enable = true;
+    settings = { };
+  };
+
+  test.stubs.nodejs = { };
+
+  nmt.script = ''
+    assertPathNotExists home-files/.npmrc
+    assertFileExists home-path/etc/profile.d/hm-session-vars.sh
+    assertFileNotRegex home-path/etc/profile.d/hm-session-vars.sh \
+      "export NPM_CONFIG_USERCONFIG="
+  '';
+}