pkgs/top-level/config.nix: add options.inHydra

pkgs/stdenv/generic/check-meta.nix

@@ -41,7 +41,8 @@ let
 
   # If we're in hydra, we can dispense with the more verbose error
   # messages and make problems easier to spot.
-  inHydra = config.inHydra or false;
+  inherit (config) inHydra;
+
   # Allow the user to opt-into additional warnings, e.g.
   # import <nixpkgs> { config = { showDerivationWarnings = [ "maintainerless" ]; }; }
   showWarnings = config.showDerivationWarnings;

pkgs/top-level/config.nix

@@ -258,6 +258,14 @@ let
         Function to handle evaluation errors and possibly output a more informative message.
       '';
     };
+
+    inHydra = mkEnableOption "" // {
+      internal = true;
+      description = ''
+        Whether the current nixpkgs instance is being evauluated by Hydra.
+        If set to true, evaluation checks will produce less verbose error messages.
+      '';
+    };
   };
 
 in