Code snippets with line numbers

The default settings for HTML compression are incompatible with the HTML produced by Jekyll (4.1.1 or earlier) for line numbers from highlighted code – both when using Kramdown code fences and when using Liquid highlight tags.

To avoid non-conforming HTML and unsatisfactory layout, HTML compression can be turned off by using the following configuration option:

compress_html:
  ignore:
    envs: all

When using Kramdown code fences, line numbers are turned on globally by the following configuration option:

kramdown:
  syntax_highlighter_opts:
    block:
      line_numbers: true

Line numbers can then be suppressed locally using Liquid tags (without the linenos option) instead of fences:

{% highlight some_language %}
Some code
{% endhighlight %}

Workarounds

To use HTML compression together with line numbers, all highlighted code needs to be wrapped using one of the following workarounds. (The variable name some_var can be changed to avoid clashes; it can also be replaced by code – but note that code=code cannot be removed).

Code fences (three backticks)

{% capture some_var %}
```some_language
Some code
```
{% endcapture %}
{% assign some_var = some_var | markdownify %}
{% include fix_linenos.html code=some_var %}

Liquid highlighting

{% capture some_var %}
{% highlight some_language linenos %}
Some code
{% endhighlight %}
{% endcapture %}
{% include fix_linenos.html code=some_var %}

Credit: The original version of the above workaround was suggested by Dmitry Hrabrov at https://github.com/penibelst/jekyll-compress-html/issues/71#issuecomment-188144901.

Examples

✅ Using code fences + workaround (will only show line numbers if enabled globally in _config.yml):

// Javascript code with syntax highlighting in fences
var fun = function lang(l) {
  dateformat.i18n = require('./lang/' + l)
  return true;
}

✅ Using liquid highlighting + workaround:

1
2
3
4

# Ruby code with syntax highlighting and fixed line numbers using Liquid
GitHubPages::Dependencies.gems.each do |gem, version|
  s.add_dependency(gem, "= #{version}")
end

❌ With the default configuration options, the following example illustrates the incorrect formatting arising from the incompatibility of HTML compression and the non-conforming HTML produced by Jekyll for line numbers:

1
2
3
4

# Ruby code with syntax highlighting and unfixed line numbers using Liquid
GitHubPages::Dependencies.gems.each do |gem, version|
  s.add_dependency(gem, "= #{version}")
end