rouge-ruby/rouge · error · InvalidRegex

regex #{@re.inspect} matches empty string, but has no predic

Error message

regex #{@re.inspect} matches empty string, but has no predicate!

What it means

Error "regex #{@re.inspect} matches empty string, but has no predicate!" thrown in rouge-ruby/rouge.

Source

Thrown at lib/rouge/regex_lexer.rb:126

            @stack.push(state)
          end
        when Array
          # [jneen] TODO: deprecate this.
          proc do |stream|
            puts "    yielding: #{tok.qualname}, #{stream[0].inspect}" if @debug
            @output_stream.call(tok, stream[0])
            for i_next_state in next_state do
              next @stack.pop if i_next_state == :pop!
              next @stack.push(@stack.last) if i_next_state == :push

              state = @states[i_next_state] || self.class.get_state(i_next_state)
              puts "    pushing :#{state.name}" if @debug
              @stack.push(state)
            end
          end
        when nil
          # cannot use an empty-matching regexp with no predicate
          raise InvalidRegex.new(re) if matches_empty

          proc do |stream|
            puts "    yielding: #{tok.qualname}, #{stream[0].inspect}" if @debug
            @output_stream.call(tok, stream[0])
          end
        end
      end
    end

    # a State is a named set of rules that can be tested for or
    # mixed in.
    #
    # @see RegexLexer.state
    class State
      attr_reader :name, :rules
      def initialize(name, rules)
        @name = name
        @rules = rules

View on GitHub (pinned to bd7dad7b09)

When it happens

Trigger: Thrown at lib/rouge/regex_lexer.rb:126 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/5ffc46af13aa5f3d. Report an issue: GitHub.