From 1bec8475a6d34b8ae60bb1c3ba91a95798c919b1 Mon Sep 17 00:00:00 2001
From: Ben Siraphob <bensiraphob@gmail.com>
Date: Tue, 14 Apr 2026 09:41:14 -0700
Subject: [PATCH] lib/modules: skip optional + ++ in evalOptionValue when no
 default

Replace `(optional (opt ? default) { ... }) ++ defs` with a direct
if/then/else. When the option has no default, this skips both the
list allocation and the ++ concat entirely. Most options do have
defaults, but even then we avoid the `optional` function call overhead
(closure + env allocation).

On NixOS minimal eval: -45K function calls (-0.93%), -3.7K list
concats (-1.93%).
---
 lib/modules.nix | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/lib/modules.nix b/lib/modules.nix
index 9bf1ac9b4d73..2b40202972ba 100644
--- a/lib/modules.nix
+++ b/lib/modules.nix
@@ -1121,11 +1121,16 @@ let
     let
       # Add in the default value for this option, if any.
       defs' =
-        (optional (opt ? default) {
-          file = head opt.declarations;
-          value = mkOptionDefault opt.default;
-        })
-        ++ defs;
+        if opt ? default then
+          [
+            {
+              file = head opt.declarations;
+              value = mkOptionDefault opt.default;
+            }
+          ]
+          ++ defs
+        else
+          defs;
 
       # Handle properties, check types, and merge everything together.
       res =