Adding NOIR to your project
NOIR is a port of the famous Rouge, a pure Ruby syntax highlighter. NOIR is not as complete as Rouge but it works, and adding other languages should be pretty easy, just a matter of porting the corresponding lexer from Rouge.
First, you need to add NOIR to your project. Unfortunately, the latest commit on NOIR is 3 years old and, by default, the project is not compatible with Crystal 1.0.0 due to the lack of a crystal version number in its
shard.yml. I made a fork here so that you can directly include it in your crystal 1.0.0 project:
dependencies: noir: github: vjousse/noir
Writing a custom parser for cr-mark-gfm
Then, as I said above, I’m using cr-mark-gfm to convert my markdown content to HTML. To be able to highlight my code on the backend, I had to override the default
Cmark::HTMLRenderer class and more especially the
def code_block(node) method that is in charge of rendering the
<code> blocks. The goal was to wire some code from NOIR here to highlight the content of the
Here is the code I put on the top of my
What I did here is that I took the code from the cr-mark-gfm HTML renderer and added the one I found in the NOIR library. By default, I’m using the
monokai theme from NOIR (there is also a solarized theme available).
Then I just have to convert my markdown to HTML as unusual. Here is the rest of my
class Post < BaseModel avram_enum Lang do Fr # 0 En # 1 end table do column title : String column content : String column teaser : String? column slug : String column filename : String column published_at : Time column lang : Post::Lang column hash : String end def md_to_html(md : String): String options = Cmark::Option.flags(ValidateUTF8, Smart, Unsafe, GithubPreLang) extensions = Cmark::Extension.flags(Table, Tasklist) nodes = Cmark.parse_gfm(md.gsub("", ""), options) renderer = PostHTMLRenderer.new(options, extensions) renderer.render(nodes) end def content_to_html : String md_to_html(self.content) end def teaser_to_html : String if teaser = self.teaser md_to_html(teaser) else "" end end end
You can find the whole file directly on Github.
Add some nice CSS
Now that we have some HTML and classes that have been added to our output, we need to colorize them. Here is how the output looks like:
NOIR provides some CSS that you can copy paste to get this result. Follow the instructions on the NOIR’s github README to compile the
ET NOIR CLI tool and execute the following command to get the CSS for the
./bin/etnoir style monokai
This should output something like the image below.
Copy paste the content to your CSS file, and you’re done. Here is a direct link to the CSS I use for this blog.
Crystal and NOIR provide a solid fundation to highlight code on the server side. Even if only 7 languages are available for now (
ruby) it should be straightforward to port other languages using some examples from Rouge.
I really enjoy playing around with the Crystal libs out there. It looks like Crystal just need a little bit more ❤️ to be the new defacto “dynamic language with an useful compiler”.
That’s all for today folks. Don’t hesitate to reach out to me if you have any question. Enjoy! 🎉