Add syntax highlighting.

src/lib.rs

@@ -237,9 +237,11 @@ pub fn generate_deck(
 
     let md_content = md_content.replace("---", "## NO_HEADING");
     let slide_adapter = plugins::SlideAdapter::new();
+    let syntax_highlighter = plugins::SyntaxHighlighter::new();
     let options = comrak::Options::default();
     let mut plugins = comrak::Plugins::default();
     plugins.render.heading_adapter = Some(&slide_adapter);
+    plugins.render.codefence_syntax_highlighter = Some(&syntax_highlighter);
     let html = comrak::markdown_to_html_with_plugins(&md_content, &options, &plugins);
 
     let generated = generated.replace("$CONTENT", &html);

src/plugins/mod.rs

@@ -1,4 +1,7 @@
 //! comrak plugins we need
 
 mod slides;
+mod syntax;
+
 pub use slides::SlideAdapter;
+pub use syntax::SyntaxHighlighter;

src/plugins/syntax.rs

@@ -0,0 +1,53 @@
+//! Our Syntax Highlighting code,
+//!
+//! A comrak plugin for adding syntax highlighting classes to code blocks.
+
+pub struct SyntaxHighlighter();
+
+impl SyntaxHighlighter {
+    pub fn new() -> SyntaxHighlighter {
+        SyntaxHighlighter()
+    }
+}
+
+impl comrak::adapters::SyntaxHighlighterAdapter for SyntaxHighlighter {
+    fn write_pre_tag(
+        &self,
+        output: &mut dyn std::io::Write,
+        attributes: std::collections::HashMap<String, String>,
+    ) -> std::io::Result<()> {
+        println!("Pre Attr: {:?}", attributes);
+        writeln!(output, "<pre>")?;
+        Ok(())
+    }
+
+    fn write_code_tag(
+        &self,
+        output: &mut dyn std::io::Write,
+        attributes: std::collections::HashMap<String, String>,
+    ) -> std::io::Result<()> {
+        println!("Code Attr: {:?}", attributes);
+        let mut lang_class = "";
+        if let Some(class) = attributes.get("class") {
+            if let Some(lang) = class.strip_prefix("language-") {
+                lang_class = lang;
+            }
+        }
+        writeln!(
+            output,
+            r#"<code data-trim data-noescape class="{lang_class}">"#
+        )?;
+        Ok(())
+    }
+
+    fn write_highlighted(
+        &self,
+        output: &mut dyn std::io::Write,
+        lang: Option<&str>,
+        code: &str,
+    ) -> std::io::Result<()> {
+        println!("Got lang {:?}", lang);
+        writeln!(output, "{}", code)?;
+        Ok(())
+    }
+}