nixos: make it possible for several modules to provide a debuginfod server

by introducing a `environment.debuginfodServers` option.

nixos/modules/config/debug-info.nix

@@ -1,4 +1,9 @@
-{ config, lib, ... }:
+{
+  config,
+  lib,
+  pkgs,
+  ...
+}:
 {
 
   options = {
@@ -23,9 +28,20 @@
       '';
     };
 
+    environment.debuginfodServers = lib.mkOption {
+      type = lib.types.listOf lib.types.str;
+      default = [ ];
+      description = ''
+        List of urls of debuginfod servers for tools like {command}`gdb` and {command}`valgrind` to use.
+
+        Unrelated to {option}`environment.enableDebugInfo`.
+      '';
     };
 
-  config = lib.mkIf config.environment.enableDebugInfo {
+  };
+
+  config = lib.mkMerge [
+    (lib.mkIf config.environment.enableDebugInfo {
 
       # FIXME: currently disabled because /lib is already in
       # environment.pathsToLink, and we can't have both.
@@ -35,6 +51,17 @@
 
       environment.variables.NIX_DEBUG_INFO_DIRS = [ "/run/current-system/sw/lib/debug" ];
 
-  };
+    })
+    (lib.mkIf (config.environment.debuginfodServers != [ ]) {
+      environment.variables.DEBUGINFOD_URLS = lib.strings.concatStringsSep " " config.environment.debuginfodServers;
+
+      environment.systemPackages = [
+        # valgrind support requires debuginfod-find on PATH
+        (lib.getBin pkgs.elfutils)
+      ];
+
+      environment.etc."gdb/gdbinit.d/nixseparatedebuginfod2.gdb".text = "set debuginfod enabled on";
+    })
+  ];
 
 }

nixos/modules/services/development/nixseparatedebuginfod.nix

@@ -101,14 +101,6 @@ in
       extra-allowed-users = [ "nixseparatedebuginfod" ];
     };
 
-    environment.variables.DEBUGINFOD_URLS = "http://${url}";
+    environment.debuginfodServers = [ "http://${url}" ];
-
-    environment.systemPackages = [
-      # valgrind support requires debuginfod-find on PATH
-      (lib.getBin pkgs.elfutils)
-    ];
-
-    environment.etc."gdb/gdbinit.d/nixseparatedebuginfod.gdb".text = "set debuginfod enabled on";
-
   };
 }