CustomTagParser mixin

Mixin for custom tag parsers.

Implement this mixin to create custom tags with custom parsing logic.

Basic Usage

class MyTag extends AbstractTag with CustomTagParser {
  MyTag(super.content, super.filters);

  @override
  Parser parser([LiquidConfig? config]) {
    return someTag('mytag', config: config);
  }
}

Custom Delimiters

When parser is called with a LiquidConfig, use the factory functions with that config to support custom delimiters:

@override
Parser parser([LiquidConfig? config]) {
  return (createTagStart(config) &
          string('mytag').trim() &
          createTagEnd(config))
      .map((_) => Tag('mytag', []));
}

Accessing Config During Evaluation

If your tag needs to re-parse content (e.g., a block tag with nested Liquid syntax), access the config from the evaluator's context:

@override
dynamic evaluate(Evaluator evaluator, Buffer buffer) {
  final content = body[0].toString();

  // Get the config to use the same delimiters as the parent template
  final config = evaluator.context.config;
  final liquid = Liquid(config: config ?? LiquidConfig.standard);

  // Re-parse and render with the correct delimiters
  final result = liquid.renderString(content, evaluator.context.all());
  buffer.write(result);
}

Variable-Style Tags

For tags that use {{ }} syntax (like {{ super() }}), override delimiterType to return TagDelimiterType.variable:

@override
TagDelimiterType get delimiterType => TagDelimiterType.variable;

@override
Parser parser([LiquidConfig? config]) {
  return (createVarStart(config) &
          string('super').trim() &
          char('(').trim() &
          char(')').trim() &
          createVarEnd(config))
      .map((_) => Tag('super', []));
}