Syntax highlight code fences

lib/mdex.ex

@@ -34,7 +34,13 @@ defmodule MDEx do
   * `:extension` - https://docs.rs/comrak/latest/comrak/struct.ComrakExtensionOptions.html
   * `:parse` - https://docs.rs/comrak/latest/comrak/struct.ComrakParseOptions.html
   * `:render` - https://docs.rs/comrak/latest/comrak/struct.ComrakRenderOptions.html
+  * `:features` - see the available options below.
+
+  ### Features Options
+
   * `:sanitize` (default `false`) - sanitize output using [ammonia](https://crates.io/crates/ammonia).\n Recommended if passing `render: [unsafe_: true]`
+  * `:syntax_highlighting` (default `"InspiredGithub`) - syntax highlight code fences using [syntect](https://crates.io/crates/syntect).
+  See a list of available themes at [struct.ThemeSet](https://docs.rs/syntect/latest/syntect/highlighting/struct.ThemeSet.html#method.load_defaults)
 
   ## Examples
 
@@ -50,7 +56,7 @@ defmodule MDEx do
       iex> MDEx.to_html("<marquee>visit https://https://beaconcms.org</marquee>", extension: [autolink: true], render: [unsafe_: true])
       "<p><marquee>visit <a href=\\"https://https://beaconcms.org\\">https://https://beaconcms.org</a></marquee></p>\\n"
 
-      iex> MDEx.to_html("# Title with <script>console.log('dangerous script')</script>", render: [unsafe_: true], sanitize: true)
+      iex> MDEx.to_html("# Title with <script>console.log('dangerous script')</script>", render: [unsafe_: true], features: [sanitize: true])
       "<h1>Title with </h1>\\n"
 
   """
@@ -59,13 +65,13 @@ defmodule MDEx do
     extension = Keyword.get(opts, :extension, %{})
     parse = Keyword.get(opts, :parse, %{})
     render = Keyword.get(opts, :render, %{})
-    sanitize = Keyword.get(opts, :sanitize, false)
+    features = Keyword.get(opts, :features, %{})
 
     opts = %MDEx.Options{
       extension: struct(MDEx.ExtensionOptions, extension),
       parse: struct(MDEx.ParseOptions, parse),
       render: struct(MDEx.RenderOptions, render),
-      sanitize: sanitize
+      features: struct(MDEx.FeaturesOptions, features)
     }
 
     Native.to_html_with_options(markdown, opts)

lib/mdex/options.ex

@@ -31,10 +31,16 @@ defmodule MDEx.RenderOptions do
             sourcepos: false
 end
 
+defmodule MDEx.FeaturesOptions do
+  @moduledoc false
+  defstruct sanitize: false,
+            syntax_highlighting: "InspiredGitHub"
+end
+
 defmodule MDEx.Options do
   @moduledoc false
   defstruct extension: %MDEx.ExtensionOptions{},
             parse: %MDEx.ParseOptions{},
             render: %MDEx.RenderOptions{},
-            sanitize: false
+            features: %MDEx.FeaturesOptions{}
 end

native/comrak_nif/src/lib.rs

@@ -2,7 +2,8 @@
 extern crate rustler;
 
 use ammonia::clean;
-use comrak::markdown_to_html;
+use comrak::plugins::syntect::SyntectAdapter;
+use comrak::{markdown_to_html, markdown_to_html_with_plugins};
 use rustler::{Env, NifResult, Term};
 use serde_rustler::to_term;
 
@@ -51,18 +52,28 @@ pub struct RenderOptions {
     pub sourcepos: bool,
 }
 
+#[derive(Debug, NifStruct)]
+#[module = "MDEx.FeaturesOptions"]
+pub struct FeaturesOptions {
+    pub sanitize: bool,
+    pub syntax_highlighting: Option<String>,
+}
+
 #[derive(Debug, NifStruct)]
 #[module = "MDEx.Options"]
 pub struct Options {
     pub extension: ExtensionOptions,
     pub parse: ParseOptions,
     pub render: RenderOptions,
-    pub sanitize: bool,
+    pub features: FeaturesOptions,
 }
 
 #[rustler::nif(schedule = "DirtyCpu")]
 fn to_html(md: &str) -> String {
-    markdown_to_html(md, &comrak::ComrakOptions::default())
+    let syntec_adapter = SyntectAdapter::new("InspiredGitHub");
+    let mut plugins = comrak::ComrakPlugins::default();
+    plugins.render.codefence_syntax_highlighter = Some(&syntec_adapter);
+    markdown_to_html_with_plugins(md, &comrak::ComrakOptions::default(), &plugins)
 }
 
 #[rustler::nif(schedule = "DirtyCpu")]
@@ -97,16 +108,30 @@ fn to_html_with_options<'a>(env: Env<'a>, md: &str, options: Options) -> NifResu
         },
     };
 
-    let unsafe_html = markdown_to_html(md, &comrak_options);
-
-    if options.sanitize {
-        let safe_html = clean(&unsafe_html);
-        to_term(env, safe_html).map_err(|err| err.into())
-    } else {
-        to_term(env, unsafe_html).map_err(|err| err.into())
+    match options.features.syntax_highlighting {
+        Some(theme) => {
+            let mut plugins = comrak::ComrakPlugins::default();
+            let syntec_adapter = SyntectAdapter::new(theme.as_str());
+            plugins.render.codefence_syntax_highlighter = Some(&syntec_adapter);
+            let unsafe_html = markdown_to_html_with_plugins(md, &comrak_options, &plugins);
+            render(env, unsafe_html, options.features.sanitize)
+        }
+        None => {
+            let unsafe_html = markdown_to_html(md, &comrak_options);
+            render(env, unsafe_html, options.features.sanitize)
+        }
     }
 }
 
+fn render(env: Env, unsafe_html: String, sanitize: bool) -> NifResult<Term> {
+    let html = match sanitize {
+        true => clean(&unsafe_html),
+        false => unsafe_html,
+    };
+
+    to_term(env, html).map_err(|err| err.into())
+}
+
 fn list_style(list_style: ListStyleType) -> comrak::ListStyleType {
     match list_style {
         ListStyleType::Dash => comrak::ListStyleType::Dash,

test/mdex_test.exs

@@ -1,4 +1,39 @@
 defmodule MDExTest do
   use ExUnit.Case
   doctest MDEx
+
+  describe "syntax highlighting" do
+    test "enabled by default" do
+      assert MDEx.to_html(~S"""
+             ```elixir
+             {:mdex, "~> 0.1"}
+             ```
+             """) ==
+               "<pre style=\"background-color:#ffffff;\"><code class=\"language-elixir\"><span style=\"color:#323232;\">{:mdex, &quot;~&gt; 0.1&quot;}\n</span></code></pre>\n"
+    end
+
+    test "change theme name" do
+      assert MDEx.to_html(
+               ~S"""
+               ```elixir
+               {:mdex, "~> 0.1"}
+               ```
+               """,
+               features: [syntax_highlighting: "base16-mocha.dark"]
+             ) ==
+               "<pre style=\"background-color:#3b3228;\"><code class=\"language-elixir\"><span style=\"color:#d0c8c6;\">{:mdex, &quot;~&gt; 0.1&quot;}\n</span></code></pre>\n"
+    end
+
+    test "can be disabled" do
+      assert MDEx.to_html(
+               ~S"""
+               ```elixir
+               {:mdex, "~> 0.1"}
+               ```
+               """,
+               features: [syntax_highlighting: nil]
+             ) ==
+               "<pre><code class=\"language-elixir\">{:mdex, &quot;~&gt; 0.1&quot;}\n</code></pre>\n"
+    end
+  end
 end