LunAST

Experimental AST processor for the Discord client's Webpack modules.

Usage

LunAST functions off of "processors". A processor has a unique ID, priority, an optional filter, and a process function. These must be registered in your index.ts file ASAP - not in a Webpack module or on the Node/host sides.

moonlight.lunast.register({
  name: "UniqueIDForTheProcessor",
  find: "something to look for",
  process(state) {
    return false;
  }
});

When a find is specified, the AST parsing will only be done on modules that match that regex/string(s). find is highly suggested, as AST parsing is much more expensive than simple string checks.

The process function will be called for every matched module. The state argument contains the LunAST instance, the ID of the matched module, some utilities, and more. When process returns true, the processor is unregistered, and will not trigger for future modules. Return true when you have found your desired module(s).

Utilities

There are various utilities accessible through state.lunast.utils.

You can use the magicAST function to turn some JavaScript code into another AST node, and then merge/replace the original AST. After you modify the AST, call the markDirty function. LunAST will not know to replace the module otherwise. It is suggested you read the estree-toolkit documentation.

process({ ast, markDirty, lunast }) {
  const node = /* do something with the AST */;
  if (node != null) {
    const replacement = lunast.utils.magicAST("return 1 + 1");
    node.replaceWith(replacement);
    markDirty();
    return true;
  }

  return false;
}

Embedding into client mods

First, create an instance of LunAST:

import LunAST from "@moonlight-mod/lunast";
const lunast = new LunAST();

Expose this instance to your extensions (before Webpack initializes) so extensions can register custom processors.

You'll then need to set a module source getter, so LunAST can retrieve the source of other modules.

lunast.setModuleSourceGetter((id) => {
  // assuming `funcs` is a Record<string, WebpackModuleFunc>
  return funcs[id].toString().replace(/\n/g, "");
});

Then, when processing a module into the Webpack chunk, give it the script to parse and patch the returned modules:

const parsed = lunast.parseScript(id, code);
if (parsed != null) {
  for (const [id, script] of Object.entries(parsed)) {
    // Patch module `id` with the contents of `script`
  }
}