Dynamically override settings at launch

[GetPsyched]

The Problem

I am creating a NixOS module that allows for the installation and configuration of ATLauncher. It would look something like this for an end-user:

programs.atlauncher = {
  enable = true;

  theme = "One Dark";

  settings = {
    enableConsole = false;
    enableTrayMenu = false;
    keepLauncherOpen = false;
  };
};

However, under the hood, this creates a symlink to **WORKING_DIR/configs/ATLauncher.json which is read-only (due to the way Nix works). This causes any imperative configuration within ATLauncher to never work as it cannot write to a read-only file.

When I saw the --config-override flag in ATLauncher, I thought this would solve this as the NixOS module could simply append all the configuration to that flag instead of overriding ATLauncher.json. However, this was apparently for internal configuration and not launcher settings.

The Solution

A --settings-override flag in ATLauncher to set launcher settings which accepts a JSON string, much like --config-override does.

Additional Information

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[eljamm]

I think adding this would solve a lot of issues with ATlauncher on NixOS.

For example, we can force "useJavaProvidedByMinecraft": false, to make the game always open with the system-provided java, or toggle settings that depend on whether something is installed or not, such as "enableFeralGamemode".

Also, perhaps we can add a setting to pass in specific java instances without having to search for them (related to #519).
For example: javaPaths: "/nix/store/openjdk-21/lib/openjdk:/nix/store/openjdk-8/lib/openjdk"