mkYarnPackage: fix uncopied resolutions field

Yarn only uses the "resolutions" field in the top-level package.json
file of a workspace. While it has been taken into account for
mkYarnWorkspace (9801e6e53dc321e860c822f7f3c370e76d218a42), it has not
been fixed for mkYarnPackage yet, which also uses the yarn workspace
mechanism under the hood.

A bit of care was needed because we don't want to introduce any IFD.

1 files changed, 11 insertions, 3 deletions

diff --git a/pkgs/development/tools/yarn2nix-moretea/yarn2nix/default.nix b/pkgs/development/tools/yarn2nix-moretea/yarn2nix/default.nix
index 6098c50df1376..e0bd54fd11a97 100644
--- a/pkgs/development/tools/yarn2nix-moretea/yarn2nix/default.nix
+++ b/pkgs/development/tools/yarn2nix-moretea/yarn2nix/default.nix
@@ -99,9 +99,17 @@ in rec {
           ""
       ) (builtins.attrNames pkgConfig));
 
-      workspaceJSON = pkgs.writeText
-        "${name}-workspace-package.json"
-        (builtins.toJSON { private = true; workspaces = ["deps/**"]; resolutions = packageResolutions; }); # scoped packages need second splat
+      # build-time JSON generation to avoid IFD
+      # see https://nixos.wiki/wiki/Import_From_Derivation
+      workspaceJSON = pkgs.runCommand "${name}-workspace-package.json"
+        {
+          nativeBuildInputs = [ pkgs.jq ];
+          inherit packageJSON;
+          passAsFile = [ "baseJSON" ];
+          baseJSON = builtins.toJSON { private = true; workspaces = [ "deps/**" ]; resolutions = packageResolutions; };
+        } ''
+        jq --slurpfile packageJSON "$packageJSON" '.resolutions = $packageJSON[0].resolutions + .resolutions' <"$baseJSONPath" >$out
+      '';
 
       workspaceDependencyLinks = lib.concatMapStringsSep "\n"
         (dep: ''