Allow for Syntect to simply generate CSS classes

examples/syntect.rs

@@ -4,7 +4,7 @@ use comrak::plugins::syntect::SyntectAdapter;
 use comrak::{markdown_to_html_with_plugins, Options, Plugins};
 
 fn main() {
-    let adapter = SyntectAdapter::new("base16-ocean.dark");
+    let adapter = SyntectAdapter::new(Some("base16-ocean.dark"));
     let options = Options::default();
     let mut plugins = Plugins::default();
 

src/main.rs

@@ -251,7 +251,7 @@ fn main() -> Result<(), Box<dyn Error>> {
     if theme.is_empty() || theme == "none" {
         syntax_highlighter = None;
     } else {
-        adapter = SyntectAdapter::new(&theme);
+        adapter = SyntectAdapter::new(Some(&theme));
         syntax_highlighter = Some(&adapter);
     }
 

src/plugins/syntect.rs

@@ -6,43 +6,68 @@ use std::collections::{hash_map, HashMap};
 use std::io::{self, Write};
 use syntect::easy::HighlightLines;
 use syntect::highlighting::{Color, ThemeSet};
-use syntect::html::{append_highlighted_html_for_styled_line, IncludeBackground};
+use syntect::html::{
+    append_highlighted_html_for_styled_line, ClassStyle, ClassedHTMLGenerator, IncludeBackground,
+};
 use syntect::parsing::{SyntaxReference, SyntaxSet};
 use syntect::util::LinesWithEndings;
 use syntect::Error;
 
 #[derive(Debug)]
 /// Syntect syntax highlighter plugin.
 pub struct SyntectAdapter {
-    theme: String,
+    theme: Option<String>,
     syntax_set: SyntaxSet,
     theme_set: ThemeSet,
 }
 
 impl SyntectAdapter {
     /// Construct a new `SyntectAdapter` object and set the syntax highlighting theme.
-    pub fn new(theme: &str) -> Self {
+    pub fn new(theme: Option<&str>) -> Self {
         SyntectAdapter {
-            theme: theme.into(),
+            theme: match theme {
+                Some(t) => Some(t.into()),
+                None => None,
+            },
             syntax_set: SyntaxSet::load_defaults_newlines(),
             theme_set: ThemeSet::load_defaults(),
         }
     }
 
     fn highlight_html(&self, code: &str, syntax: &SyntaxReference) -> Result<String, Error> {
-        // syntect::html::highlighted_html_for_string, without the opening/closing <pre>.
-        let theme = &self.theme_set.themes[&self.theme];
-        let mut highlighter = HighlightLines::new(syntax, theme);
         let mut output = String::new();
-        let bg = theme.settings.background.unwrap_or(Color::WHITE);
-
-        for line in LinesWithEndings::from(code) {
-            let regions = highlighter.highlight_line(line, &self.syntax_set)?;
-            append_highlighted_html_for_styled_line(
-                &regions[..],
-                IncludeBackground::IfDifferent(bg),
-                &mut output,
-            )?;
+
+        match &self.theme {
+            Some(theme) => {
+                // syntect::html::highlighted_html_for_string, without the opening/closing <pre>.
+                let theme = &self.theme_set.themes[theme];
+                let mut highlighter = HighlightLines::new(syntax, theme);
+
+                let bg = theme.settings.background.unwrap_or(Color::WHITE);
+
+                for line in LinesWithEndings::from(code) {
+                    let regions = highlighter.highlight_line(line, &self.syntax_set)?;
+                    append_highlighted_html_for_styled_line(
+                        &regions[..],
+                        IncludeBackground::IfDifferent(bg),
+                        &mut output,
+                    )?;
+                }
+            }
+            None => {
+                // fall back to HTML classes
+                let mut html_generator = ClassedHTMLGenerator::new_with_class_style(
+                    syntax,
+                    &self.syntax_set,
+                    ClassStyle::Spaced,
+                );
+                for line in LinesWithEndings::from(code) {
+                    html_generator
+                        .parse_html_for_line_which_includes_newline(line)
+                        .unwrap();
+                }
+                output = html_generator.finalize();
+            }
         }
         Ok(output)
     }
@@ -82,16 +107,26 @@ impl SyntaxHighlighterAdapter for SyntectAdapter {
         output: &mut dyn Write,
         attributes: HashMap<String, String>,
     ) -> io::Result<()> {
-        let theme = &self.theme_set.themes[&self.theme];
-        let colour = theme.settings.background.unwrap_or(Color::WHITE);
-
-        let style = format!(
-            "background-color:#{:02x}{:02x}{:02x};",
-            colour.r, colour.g, colour.b
-        );
+        match &self.theme {
+            Some(theme) => {
+                let theme = &self.theme_set.themes[theme];
+                let colour = theme.settings.background.unwrap_or(Color::WHITE);
+
+                let style = format!(
+                    "background-color:#{:02x}{:02x}{:02x};",
+                    colour.r, colour.g, colour.b
+                );
+
+                let mut pre_attributes = SyntectPreAttributes::new(attributes, &style);
+                html::write_opening_tag(output, "pre", pre_attributes.iter_mut())
+            }
+            None => {
+                let mut attributes: HashMap<String, String> = HashMap::new();
+                attributes.insert(String::from("class"), String::from("syntax-highlighting"));
 
-        let mut pre_attributes = SyntectPreAttributes::new(attributes, &style);
-        html::write_opening_tag(output, "pre", pre_attributes.iter_mut())
+                html::write_opening_tag(output, "pre", attributes)
+            }
+        }
     }
 
     fn write_code_tag(
@@ -191,7 +226,7 @@ impl SyntectAdapterBuilder {
     /// - `theme_set`: [`ThemeSet::load_defaults()`]
     pub fn build(self) -> SyntectAdapter {
         SyntectAdapter {
-            theme: self.theme.unwrap_or_else(|| "InspiredGitHub".into()),
+            theme: Some(self.theme.unwrap_or_else(|| "InspiredGitHub".into())),
             syntax_set: self
                 .syntax_set
                 .unwrap_or_else(SyntaxSet::load_defaults_newlines),

src/tests/plugins.rs

@@ -88,8 +88,8 @@ fn heading_adapter_plugin() {
 
 #[test]
 #[cfg(feature = "syntect")]
-fn syntect_plugin() {
-    let adapter = crate::plugins::syntect::SyntectAdapter::new("base16-ocean.dark");
+fn syntect_plugin_with_base16_ocean_dark_theme() {
+    let adapter = crate::plugins::syntect::SyntectAdapter::new(Some("base16-ocean.dark"));
 
     let input = concat!("```rust\n", "fn main<'a>();\n", "```\n");
     let expected = concat!(
@@ -104,3 +104,23 @@ fn syntect_plugin() {
 
     html_plugins(input, expected, &plugins);
 }
+
+#[test]
+#[cfg(feature = "syntect")]
+fn syntect_plugin_with_css_classes() {
+    let adapter = crate::plugins::syntect::SyntectAdapter::new(None);
+
+    let input = concat!("```rust\n", "fn main<'a>();\n", "```\n");
+    let expected = concat!(
+        "<pre class=\"syntax-highlighting\"><code class=\"language-rust\">",
+        "<span class=\"source rust\"><span class=\"meta function rust\"><span class=\"meta function rust\"><span class=\"storage type function rust\">fn</span> </span><span class=\"entity name function rust\">main</span></span><span class=\"meta generic rust\"><span class=\"punctuation definition generic begin rust\">&lt;</span>",
+        "<span class=\"storage modifier lifetime rust\">&#39;a</span><span class=\"punctuation definition generic end rust\">&gt;</span></span><span class=\"meta function rust\"><span class=\"meta function parameters rust\"><span class=\"punctuation section parameters begin rust\">(</span></span><span class=\"meta function rust\">",
+        "<span class=\"meta function parameters rust\"><span class=\"punctuation section parameters end rust\">)</span></span></span></span><span class=\"punctuation terminator rust\">;</span>\n</span>",
+        "</code></pre>\n",
+    );
+
+    let mut plugins = Plugins::default();
+    plugins.render.codefence_syntax_highlighter = Some(&adapter);
+
+    html_plugins(input, expected, &plugins);
+}