Starting in 3.4.1, the following Rouge code generates a warning in verbose mode about the use of opts with Lexer.lex:

old_verbose, $VERBOSE = $VERBOSE, nil
require 'rouge'
$VERBOSE = old_verbose

source = 'puts "Hello, World!"'
formatter = Rouge::Formatters::HTML.new
lexer = Rouge::Lexer.find 'ruby'
formatter.format(lexer.lex(source))

The following message is printed when invoked using ruby -w:

The use of opts with Lexer.lex is deprecated
The use of opts with Lexer.lex is deprecated

The problem is that Rouge itself is passing the options, not the user. See https://github.com/rouge-ruby/rouge/blob/master/lib/rouge/lexer.rb#L426-L429.

This warning did not occur in 3.4.0, so it has to do with this change: 6835352