From a0ac2ae35e45b28fe071300de17e51d0ef610507 Mon Sep 17 00:00:00 2001
From: Alexander Ried <ried@mytum.de>
Date: Sat, 22 Oct 2016 20:24:56 +0200
Subject: [PATCH] stdenv: throwEvalHelp performance (#19779)

---
 pkgs/stdenv/generic/default.nix | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/pkgs/stdenv/generic/default.nix b/pkgs/stdenv/generic/default.nix
index 372fd3cfa52..978da2e1907 100644
--- a/pkgs/stdenv/generic/default.nix
+++ b/pkgs/stdenv/generic/default.nix
@@ -128,8 +128,7 @@ let
       throwEvalHelp = { reason, errormsg }:
         # uppercase the first character of string s
         let up = s: with lib;
-          let cs = lib.stringToCharacters s;
-          in concatStrings (singleton (toUpper (head cs)) ++ tail cs);
+          (toUpper (substring 0 1 s)) + (substring 1 (stringLength s) s);
         in
         assert builtins.elem reason ["unfree" "broken" "blacklisted"];