nixos/lib: Add featureFlags, use it for minimal modules

1 files changed, 22 insertions, 2 deletions

diff --git a/nixos/lib/default.nix b/nixos/lib/default.nix
index 41ae2d863e0..2b3056e0145 100644
--- a/nixos/lib/default.nix
+++ b/nixos/lib/default.nix
@@ -1,5 +1,25 @@
-{ lib ? import ../../lib, ... }:
 let
+  # The warning is in a top-level let binding so it is only printed once.
+  minimalModulesWarning = warn "lib.nixos.evalModules is experimental and subject to change. See nixos/lib/default.nix" null;
+  inherit (nonExtendedLib) warn;
+  nonExtendedLib = import ../../lib;
+in
+{ # Optional. Allows an extended `lib` to be used instead of the regular Nixpkgs lib.
+  lib ? nonExtendedLib,
+
+  # Feature flags allow you to opt in to unfinished code. These may change some
+  # behavior or disable warnings.
+  featureFlags ? {},
+
+  # This file itself is rather new, so we accept unknown parameters to be forward
+  # compatible. This is generally not recommended, because typos go undetected.
+  ...
+}:
+let
+  seqIf = cond: if cond then builtins.seq else a: b: b;
+  # If cond, force `a` before returning any attr
+  seqAttrsIf = cond: a: lib.mapAttrs (_: v: seqIf cond a v);
+
   eval-config-minimal = import ./eval-config-minimal.nix { inherit lib; };
 in
 /*
@@ -7,7 +27,7 @@ in
   using a binding like `nixosLib = import (nixpkgs + "/nixos/lib") { }`.
 */
 {
-  inherit (eval-config-minimal)
+  inherit (seqAttrsIf (!featureFlags?minimalModules) minimalModulesWarning eval-config-minimal)
     evalModules
     ;
 }