rouge-ruby/rouge · error · ArgumentError

Expected an instance of Rouge::Formatters::HTML, got #{forma

Error message

Expected an instance of Rouge::Formatters::HTML, got #{formatter.class}. Try HTML, HTMLDebug, or HTMLInline.

What it means

Error "Expected an instance of Rouge::Formatters::HTML, got #{formatter.class}. Try HTML, HTMLDebug, or HTMLInline." thrown in rouge-ruby/rouge.

Source

Thrown at lib/rouge/formatters/html.rb:20

# frozen_string_literal: true

module Rouge
  module Formatters
    # Transforms a token stream into HTML output.
    class HTML < Formatter
      TABLE_FOR_ESCAPE_HTML = {
        '&' => '&amp;',
        '<' => '&lt;',
        '>' => '&gt;',
        "\r" => "",
      }.freeze

      ESCAPE_REGEX = /[&<>\r]/.freeze

      def self.assert_html_formatter!(formatter)
        return formatter if formatter.respond_to?(:span)

        raise ArgumentError.new("Expected an instance of Rouge::Formatters::HTML, got #{formatter.class}. Try HTML, HTMLDebug, or HTMLInline.")
      end

      tag 'html'

      # @yield the html output.
      def stream(tokens, &b)
        tokens.each { |tok, val| yield span(tok, val) }
      end

      def span(tok, val)
        return val if escape?(tok)

        safe_span(tok, escape_special_html_chars(val))
      end

      def safe_span(tok, safe_val)
        if tok == Token::Tokens::Text
          safe_val

View on GitHub (pinned to bd7dad7b09)

When it happens

Trigger: Thrown at lib/rouge/formatters/html.rb:20 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of rouge-ruby/rouge@bd7dad7b09 (2026-08-23). Data as JSON: /api/errors/141d6cd136aa55d9. Report an issue: GitHub.