How to make autoformat work with custom embeds

[Yoeri-z]

I am trying to make a custom autoformatter that autoformats LaTeX, it does this by replacing some text range for a latex embed.
I keep running into this assertion fail when trying to compose the document with the delta, it seems like there is some race condition going on but i can not for the life of me figure out what is going wrong, this post is my last resort.

class AutoFormatLatex extends AutoFormat {
  const AutoFormatLatex();

  @override
  AutoFormatResult? apply(
    ParchmentDocument document,
    int position,
    String data,
  ) {
    ...
    //  The range i finally derive is valid, i left out some code
    final debugText = document.toPlainText();
    print(debugText); //prints "Testing $latex$"
    print(
      debugText.substring(
        startIndex,
       startIndex + contentLength,
      ),
    ); //prints "$latex$"

    final change = Delta()
      ..retain(startIndex)
      ..delete(contentLength)
      ..insert(
        EmbeddableObject(
          'math',
          inline: true,
          data: {'formula': candidate.substring(firstIndex + 1)},
        ),
      );

    final undo = change.invert(documentDelta);
    document.compose(change, .local);

    return AutoFormatResult(
      change: change,
      undo: undo,
      undoPositionCandidate: firstIndex + 1,
      selection: TextSelection.collapsed(offset: firstIndex + 1),
      undoSelection: TextSelection.collapsed(offset: position),
    );
  }
}

For the design of this formatter i took some inspiration from the MarkdownInlineShortcuts formatter this package has, it does the same method of composing the document before returning autoformat result.

If i wrap the document.compose call with a trycatch block the code behaves like expected but i get out of range errors when typing after so it seems like the underlying delta of the document is now out of sync with the actual nodes.

These are errors i am getting:

══╡ EXCEPTION CAUGHT BY SERVICES LIBRARY ╞══════════════════════════════════════════════════════════
The following StateError was thrown during method call TextInputClient.updateEditingStateWithDeltas:
Bad state: Compose produced inconsistent results. This is likely due to a bug in the library. Tried
to compose change retain⟨ 8 ⟩
insert⟨ Instance of 'EmbeddableObject' ⟩
delete⟨ 7 ⟩ from ChangeSource.local.

When the exception was thrown, this was the stack:
#0      ParchmentDocument.compose (package:parchment/src/document.dart:254:7)
#1      AutoFormatLatex.apply (package:science_notes/ui/features/editor/latex_embed_builder.dart:104:14)
#2      AutoFormats.run (package:fleather/src/widgets/autoformats.dart:95:38)
.....
Another exception was thrown: 'package:parchment/src/document/node.dart': Failed assertion: line 246 pos 12: 'offset >= 0 && offset <= length': is not true.
Another exception was thrown: Range start 15 is out of text of length 10
Another exception was thrown: 'package:parchment/src/document/node.dart': Failed assertion: line 246 pos 12: 'offset >= 0 && offset <= length': is not true.
Another exception was thrown: Range start 15 is out of text of length 10
.....

If someone could help or suggest a different way to do this it would be much appreciated!

[Yoeri-z]

I was able to solve my issue (right after making the post, as usual) by using document.replace instead of document.compose.

    final change = document.replace(
      position - candidate.length + firstIndex,
      contentLength,
      EmbeddableObject(
        'math',
        inline: true,
        data: {'formula': candidate.substring(firstIndex + 1)},
      ),
    );