• Is new feature

Description of suggestion or shortcoming:

We've had a few code formatting bugs before. These can be really annoying for users, as they can be difficult to detect and debug (they often don't leave errors, just change code).

It seems good to check the AST before+after, and make sure these are identical semantically. If they aren't, throw an error, instead of formatting.

I started trying this.

In useFormatSIquiggleExtension.ts

export async function formatSquiggle(view: EditorView | undefined) {
  if (!view) return;
  const code = view.state.doc.toString();
  const before = JSON.stringify(parse(code));
  const { formatted, cursorOffset } = await prettier.formatWithCursor(code, {
    parser: "squiggle",
    plugins: [prettierSquigglePlugin],
    cursorOffset: view.state.selection.main.to,
  });
  const after = JSON.stringify(parse(formatted));
  console.log("AST", before === after);
  console.log(before);
  console.log(after);
  view.dispatch({
    changes: {
      from: 0,
      to: view.state.doc.length,
      insert: formatted,
    },
    selection: {
      anchor: cursorOffset,
    },
  });
}

Here, I found that the AST does change based on the location objects, which makes sense, even though these don't have semantic meaning. So we'd need to detect changes other than location changes.

One easy way to do this is to write a single-use script that converts the data into JSON, then scrubs the locations, then checks for equality.

A better way would probably be something like adding parameterized isEqual methods for ASTNode.