Get inner_block html as string in Phoenix.Component

I am creating a syntax highlighter component using Phoenix.Component and Makeup

defmodule Indy.Bootstrap.Code do
 use Phoenix.Component
 import Indy.Bootstrap.AssignUtils

 def highlight(assigns) do
   makeup_code = 
     Makeup.Lexers.Bootstrap.HTMLLexer.lex(assigns[:code] || "")
     |> Makeup.Formatters.HTML.HTMLFormatter.format_inner_as_binary([])
   assigns = assign(assigns, :makeup_code, makeup_code)
   ~H"""
<pre class="chroma"><code class="language-html"><%= Phoenix.HTML.raw(@makeup_code) %></code></pre>
   """ 
 end
end

Using above component, I have to pass code snippet using code attribute.

<.hightlight code="<h1>This is a heading</h1>"></.highlight>

I want to pass code as inner_block. But I am unable to figure out how to access the inner_block as string.

<.hightlight>
<h1>This is a heading</h1>
</.highlight>

Any pointers or help on how can I achieve this?

Solved using the following code

render_slot(@inner_block) 
|> Phoenix.HTML.html_escape() 
|> Phoenix.HTML.safe_to_string()
|> Makeup.Lexers.Bootstrap.HTMLLexer.lex() 
|> Makeup.Formatters.HTML.HTMLFormatter.format_inner_as_binary([]) 
|> Phoenix.HTML.raw()

I am using &lt; and &gt; as escape characters for embedding live view component code.

<.highlight>
  <h1>This is heading</h1>
  <p> This is a paragraph</p>
  &lt;.alert primary&gt;&lt;/.alert&gt;
</.highlight>

will render as
image

I am replacing &lt; to < and &gt; to > inside Makeup.Lexers.Bootstrap.HTMLLexer.lex.

Finally code will look something like this.

defmodule Indy.Bootstrap.Code do
  use Phoenix.Component
  import Indy.Bootstrap.AssignUtils

  def highlight(assigns) do
    ~H"""
    <pre class="chroma"><code class="language-html"><%= 
      render_slot(@inner_block) 
      |> Phoenix.HTML.html_escape() 
      |> Phoenix.HTML.safe_to_string() 
      |> Makeup.Lexers.Bootstrap.HTMLLexer.lex() 
      |> Makeup.Formatters.HTML.HTMLFormatter.format_inner_as_binary([]) 
      |> Phoenix.HTML.raw() %></code></pre>
    """
  end
end

Let me know if you have any other solution or you see problems with this approach.

1 Like

I had a hard time getting the syntax highlighter to work using makeup - had to spend a lot of time understanding makeup and makeup_html. I have used syntax highlighters like highlight.js, Pygments, Prism.js in the past.

Pygments is an inspiration for makeup - but the output differs between both. makeup_html lexer generates tokens slightly differently when compared Pygments. I had logged couple of bugs on makeup_html repository.

I had to modify the default lexer add a function to lex non standard html elements - Makeup.Lexers.Bootstrap.HTMLLexer.lex.

Leaving these notes here so that others can save some time if they have to highlight code using makeup and phoenix components

1 Like

I’d suggest moving the formatting out of the heex sigil:

  def highlight(assigns) do
    formatted = 
      assigns.inner_block
      |> render_slot() 
      |> Phoenix.HTML.html_escape() 
      |> Phoenix.HTML.safe_to_string() 
      |> Makeup.Lexers.Bootstrap.HTMLLexer.lex() 
      |> Makeup.Formatters.HTML.HTMLFormatter.format_inner_as_binary([]) 
      |> Phoenix.HTML.raw()

    assigns = assign(assigns, :formatted, formatted)

    ~H"""
    <pre class="chroma"><code class="language-html"><%= @formatted %></code></pre>
    """
  end

Besides being easier to maintain it should also make it clear that the formatted code is not granularly change tracked when used in LiveView.

1 Like

I am afraid the above code does not work - render_slot() macro expansion outside of ~H will fail with the following message:

== Compilation error in file lib/indy_bootstrap/bootstrap/code.ex ==
** (CompileError) lib/indy_bootstrap/bootstrap/code.ex:8: undefined variable "changed" (context Phoenix.LiveView.Engine)
    (elixir 1.13.0) expanding macro: Kernel.var!/2
    (indy_bootstrap 0.1.0) lib/indy_bootstrap/bootstrap/code.ex:8: Indy.Bootstrap.Code.highlight/1
    (phoenix_live_view 0.17.5) expanding macro: Phoenix.LiveView.Helpers.render_slot/1
    (indy_bootstrap 0.1.0) lib/indy_bootstrap/bootstrap/code.ex:8: Indy.Bootstrap.Code.highlight/1
    (elixir 1.13.0) expanding macro: Kernel.|>/2
    (indy_bootstrap 0.1.0) lib/indy_bootstrap/bootstrap/code.ex:13: Indy.Bootstrap.Code.highlight/1
Compiling 1 file (.ex)

Thank you @LostKobrakai I get your point - i had written similar code for other components.