Rouge gem not showing line breaks in formatted code?

Question

I have followed minimal examples using the rouge gem here (i.e. the documentation), as well as here and here.

Everything working, except that line breaks in the code aren't appearing.

To be explicit, code like this

def plus_two(x)
  x + 2
end

has the colours highlighted correctly, but is rendered across one line, like so

def plus_two(x) x + 2 end 

How can I make it render with the line breaks (just as in the code file)

Answer 1

Change

require 'rouge'
source = "def plus_two(x)\n  x + 2\nend"
formatter = Rouge::Formatters::HTML.new
lexer = Rouge::Lexers::R.new
@code = formatter.format(lexer.lex(source)) 

to

require 'rouge'
source = "def plus_two(x)\n  x + 2\nend"
formatter = Rouge::Formatters::HTML.new
formatter = Rouge::Formatters::HTMLLinewise.new(formatter, class: 'line-%i')
lexer = Rouge::Lexers::R.new
@code = formatter.format(lexer.lex(source))  

More formatting options here