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# frozen_string_literal: true
require 'rouge/plugins/common_mark'
require 'rouge/plugins/redcarpet'
module Banzai
module Filter
# HTML Filter to highlight fenced code blocks
#
class SyntaxHighlightFilter < HTML::Pipeline::Filter
def call
doc.search('pre > code').each do |node|
highlight_node(node)
end
doc
end
def highlight_node(node)
css_classes = +'code highlight js-syntax-highlight'
lang = node.attr('lang')
retried = false
if use_rouge?(lang)
lexer = lexer_for(lang)
language = lexer.tag
else
lexer = Rouge::Lexers::PlainText.new
language = lang
end
begin
code = Rouge::Formatters::HTMLGitlab.format(lex(lexer, node.text), tag: language)
css_classes << " #{language}" if language
rescue
# Gracefully handle syntax highlighter bugs/errors to ensure users can
# still access an issue/comment/etc. First, retry with the plain text
# filter. If that fails, then just skip this entirely, but that would
# be a pretty bad upstream bug.
return if retried
language = nil
lexer = Rouge::Lexers::PlainText.new
retried = true
retry
end
highlighted = %(<pre class="#{css_classes}" lang="#{language}" v-pre="true"><code>#{code}</code></pre>)
# Extracted to a method to measure it
replace_parent_pre_element(node, highlighted)
end
private
# Separate method so it can be instrumented.
def lex(lexer, code)
lexer.lex(code)
end
def lexer_for(language)
(Rouge::Lexer.find(language) || Rouge::Lexers::PlainText).new
end
def replace_parent_pre_element(node, highlighted)
# Replace the parent `pre` element with the entire highlighted block
node.parent.replace(highlighted)
end
def use_rouge?(language)
%w(math mermaid plantuml).exclude?(language)
end
end
end
end
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