From 610408381746ee3e4c5b25f04b6db12c8128299b Mon Sep 17 00:00:00 2001
From: Sergei Trofimovich <slyich@gmail.com>
Date: Sun, 31 Dec 2023 11:40:48 +0000
Subject: [PATCH] build-support/fetchgithub: fix metadata eval for arguments
 without locations

Without the change metadata evaluation fails on package like
`zammad.src` where no fields are defined in `.nix `files:

    src = fetchFromGitHub (lib.importJSON ./source.json);

There evaluation fails as:

    $ nix-instantiate --strict --eval --expr 'with import ./. {}; zammad.src.meta'
    error:
           23|     # to indicate where derivation originates, similar to make-derivation.nix's mkDerivation
           24|     position = "${position.file}:${toString position.line}";
             |     ^
           25|   };
       error: value is null while a set was expected

After the change evaluation succeeds as:

    $ nix-instantiate --strict --eval --expr 'with import ./. {}; zammad.src.meta'
    { homepage = "https://github.com/zammad/zammad"; }
---
 pkgs/build-support/fetchgithub/default.nix | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pkgs/build-support/fetchgithub/default.nix b/pkgs/build-support/fetchgithub/default.nix
index a2498700b545..231c0fb622b9 100644
--- a/pkgs/build-support/fetchgithub/default.nix
+++ b/pkgs/build-support/fetchgithub/default.nix
@@ -19,7 +19,7 @@ let
   baseUrl = "https://${githubBase}/${owner}/${repo}";
   newMeta = meta // {
     homepage = meta.homepage or baseUrl;
-
+  } // lib.optionalAttrs (position != null) {
     # to indicate where derivation originates, similar to make-derivation.nix's mkDerivation
     position = "${position.file}:${toString position.line}";
   };