lib.types.deferredModule: Improve reported location

lib/tests/modules.sh

@@ -198,7 +198,7 @@ checkConfigOutput '^true$' config.submodule.enable ./declare-submoduleWith-path.
 # default module is merged into nodes.foo
 checkConfigOutput '"beta"' config.nodes.foo.settingsDict.c ./deferred-module.nix
 # errors from the default module are reported with accurate location
-checkConfigError 'In `default from the-file-that-contains-the-bad-config.nix'\'': "bogus"' config.nodes.foo.bottom ./deferred-module.nix
+checkConfigError 'In `the-file-that-contains-the-bad-config.nix, via option default'\'': "bogus"' config.nodes.foo.bottom ./deferred-module.nix
 
 # Check the file location information is propagated into submodules
 checkConfigOutput the-file.nix config.submodule.internalFiles.0 ./submoduleFiles.nix

lib/types.nix

@@ -544,7 +544,7 @@ rec {
       name = "deferredModule";
       description = "module";
       check = t: isAttrs t || isFunction t;
-      merge = loc: defs: map (def: lib.setDefaultModuleLocation "${showOption loc} from ${def.file}" def.value) defs;
+      merge = loc: defs: map (def: lib.setDefaultModuleLocation "${def.file}, via option ${showOption loc}" def.value) defs;
     };
 
     # The type of a type!