buildRustPackage fails at cargoInstallHook

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Hi all, I’ve been trying to override the source of the alacritty package with this fork: alacritty-smooth-cursor

I’ve managed to cobble together an override from previous posts on discourse but I’m running into the bellow error:

Executing cargoInstallHook
Error at 600:3: Expected ``` and a newline to begin literal block

I’ve looked at the docks for buildRustPackage below, and if I understand it and my logs correctly, the package has built successfully, however its failing to install it to the nix store? : nixpkgs/doc/languages-frameworks/rust.section.md at 27ef4a3cd624034766e817853df917466de0200e · NixOS/nixpkgs · GitHub

Can post further logs from the failed build if needed, but i didn’t think they were relevant. Any info on how to fix this would be much appreciated!

Edit - forgot to add the overlay I’m using:

pkgs.alacritty.override (old: {
  rustPlatform = old.rustPlatform // {
    buildRustPackage = args: old.rustPlatform.buildRustPackage (args// {
      src = pkgs.fetchFromGitHub {
        owner = "GregTheMadMonk";
        repo = "alacritty-smooth-cursor";
        rev = "303a92ea57a074bb50ff016c8da7a0aeae897b1a";
        hash = "sha256-aoel3P7MnO39ekBJPaTnaizJkbUaOS7sy1ktwow9JN8=";
      };

      cargoHash = "sha256-2kLlB6YXZZYX+HtKcdjr9z9hh8AW54Dkc1bLWjueKVQ=";
    });
  };
});