From d6ebd537e5d212995984152d57e16029b3726de5 Mon Sep 17 00:00:00 2001
From: Robert Hensing <robert@roberthensing.nl>
Date: Sun, 31 Oct 2021 19:10:13 +0100
Subject: [PATCH] lib/modules: Short-circuit unmatchedDefns when configs is
 empty

---
 lib/modules.nix | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/lib/modules.nix b/lib/modules.nix
index 46ae3f136310..b2ae51c8e618 100644
--- a/lib/modules.nix
+++ b/lib/modules.nix
@@ -430,10 +430,16 @@ rec {
 
       # an attrset 'name' => list of unmatched definitions for 'name'
       unmatchedDefnsByName =
-        # Propagate all unmatched definitions from nested option sets
-        mapAttrs (n: v: v.unmatchedDefns) resultsByName
-        # Plus the definitions for the current prefix that don't have a matching option
-        // removeAttrs defnsByName' (attrNames matchedOptions);
+        if configs == []
+        then
+          # When no config values exist, there can be no unmatched config, so
+          # we short circuit and avoid evaluating more _options_ than necessary.
+          {}
+        else
+          # Propagate all unmatched definitions from nested option sets
+          mapAttrs (n: v: v.unmatchedDefns) resultsByName
+          # Plus the definitions for the current prefix that don't have a matching option
+          // removeAttrs defnsByName' (attrNames matchedOptions);
     in {
       inherit matchedOptions;