From 6985598153ca90aa17d184d92438c57e4ffdfc2f Mon Sep 17 00:00:00 2001
From: Someone <else@someonex.net>
Date: Fri, 14 Feb 2025 09:50:18 +0000
Subject: [PATCH] doc: recursive-nix: advertise requiredSystemFeatures

It's best we teach users that the "foo" derivation is less than pure in the sense that it cannot be built just on any system, in particular that builders cannot be selected arbitrarily but based on their system-features. The `"recursive-nix"` system-feature is automatically defined by `--extra-experimental-features recursive-nix`
---
 src/libutil/experimental-features.cc | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/libutil/experimental-features.cc b/src/libutil/experimental-features.cc
index dba5893a8..158e202d1 100644
--- a/src/libutil/experimental-features.cc
+++ b/src/libutil/experimental-features.cc
@@ -125,6 +125,8 @@ constexpr std::array<ExperimentalFeatureDetails, numXpFeatures> xpFeatureDetails
 
             runCommand "foo"
               {
+                 # Optional: let Nix know "foo" requires the experimental feature
+                 requiredSystemFeatures = [ "recursive-nix" ];
                  buildInputs = [ nix jq ];
                  NIX_PATH = "nixpkgs=${<nixpkgs>}";
               }