nixos/networking: add its own fqdn to extraHosts

nixos/common.nix

@@ -4,6 +4,7 @@
   lib,
   pkgs,
   self,
+  config,
   ...
 }:
 let
@@ -92,6 +93,22 @@ in
   networking = {
     networkmanager.enable = true;
 
+    extraHosts =
+      let
+        subdomains = [ "" ];
+      in
+      builtins.foldl' (
+        hosts-acc: domain-prefix:
+        let
+          host = "${domain-prefix}${config.networking.fqdn}";
+        in
+        hosts-acc
+        + ''
+          127.0.0.1 ${host}
+          ::1 ${host}
+        ''
+      ) "" subdomains;
+
     firewall = {
       enable = true;