fetchFromGitHub: perserve originating position

pkgs/build-support/fetchgithub/default.nix

@@ -10,8 +10,18 @@
 }@args:
 
 let
+
+  position = (if args.meta.description or null != null
+    then builtins.unsafeGetAttrPos "description" args.meta
+    else builtins.unsafeGetAttrPos "rev" args
+  );
   baseUrl = "https://${githubBase}/${owner}/${repo}";
-  newMeta = meta // { homepage = meta.homepage or baseUrl; };
+  newMeta = meta // {
+    homepage = meta.homepage or baseUrl;
+
+    # to indicate where derivation originates, similar to make-derivation.nix's mkDerivation
+    position = "${position.file}:${toString position.line}";
+  };
   passthruAttrs = removeAttrs args [ "owner" "repo" "rev" "fetchSubmodules" "forceFetchGit" "private" "githubBase" "varPrefix" ];
   varBase = "NIX${if varPrefix == null then "" else "_${varPrefix}"}_GITHUB_PRIVATE_";
   useFetchGit = fetchSubmodules || (leaveDotGit == true) || deepClone || forceFetchGit || (sparseCheckout != "");