just-the-docs/docs/ui-components/line-nos.md

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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:

{% highlight yaml %} compress_html: ignore: envs: all {% endhighlight %}

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

{% highlight yaml %} kramdown: syntax_highlighter_opts: block: line_numbers: true {% endhighlight %}

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

{% highlight yaml %} {% raw %}{% highlight some_language %} Some code {% endhighlight %}{% endraw %} {% 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)

{% highlight default %} {% raw %}{% capture some_var %}

Some code

{% endcapture %} {% assign some_var = some_var | markdownify %} {% include fix_linenos.html code=some_var %}{% endraw %} {% endhighlight %}

Liquid highlighting

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

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):

{% capture code_fence %}

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

{% endcapture %} {% assign code_fence = code_fence | markdownify %} {% include fix_linenos.html code=code_fence %}

✅ Using liquid highlighting + workaround:

{% capture code %} {% highlight ruby linenos %}

Ruby code with syntax highlighting and fixed line numbers using Liquid

GitHubPages::Dependencies.gems.each do |gem, version| s.add_dependency(gem, "= #{version}") end {% endhighlight %} {% endcapture %} {% include fix_linenos.html code=code %} {% assign code = nil %}

Narrow code stays close to the line numbers:

{% capture code %} {% highlight ruby linenos %} def foo puts 'foo' end {% endhighlight %} {% endcapture %} {% include fix_linenos.html code=code %} {% assign code = nil %}

❌ With the compression options used for the theme docs, 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:

{% highlight ruby linenos %} def foo puts 'foo' end {% endhighlight %}