Made clangd work and recognize C headers, see https://www.reddit.com/r/NixOS/comments/1d7zvgu/nvim_cant_find_standard_library_headers/

for troubleshooting/reference if it happens again

.config/nvim/lua/custom/config/language-servers.lua

@@ -14,6 +14,7 @@ return {
         },
     }, -- lua
     clangd = {
+        mason = false,
         cmd = {
             'clangd',
             '--background-index',

.config/nvim/lua/custom/plugins/nvim-lspconfig.lua

@@ -14,6 +14,9 @@ return {
                 local ensure_installed = vim.tbl_filter(function(key)
                     local server = language_servers[key]
                     if type(server) == 'table' then
+                        if server.mason ~= nil then
+                            return server.mason
+                        end
                         return true
                     else
                         return server

hosts/laptop-nixos/configuration.nix

@@ -65,9 +65,6 @@
   # Enable touchpad support (enabled default in most desktopManager).
   # services.xserver.libinput.enable = true;
 
-  # Enable dynamic linking of applications that are not in nixpkgs (for vim LSPs for example).
-  programs.nix-ld.enable = true;
-
   # Allow sudo without a password if in "wheel" group.
   security.sudo.wheelNeedsPassword = false;
 
@@ -98,6 +95,14 @@
   environment.systemPackages = with pkgs; [
     glib-networking
     openssl
+    clang
+    clang-tools
+  ];
+
+  # Enable dynamic linking of applications that are not in nixpkgs (for vim LSPs for example).
+  programs.nix-ld.enable = true;
+  programs.nix-ld.libraries = with pkgs; [
+    stdenv.cc.cc
   ];
 
   # Some programs need SUID wrappers, can be configured further or are