Replace syntect with giallo for syntax highlighting.

converters/html/CHANGELOG.md

@@ -358,6 +358,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Changed
 
+- **Syntax highlighting now uses giallo instead of syntect** — both inline-style and
+  class-based HTML output use giallo's built-in grammars and themes. The preferred
+  attributes are now `:highlight-style:` and `:highlight-css:`, while the legacy
+  `:syntect-style:` and `:syntect-css:` names remain supported.
 - **Use shared `replace_apostrophes` from converters-core** — smart apostrophe logic moved to
   converters-core for reuse across converters.
 - **Use `strip_quotes` for attribute value handling** — replaced manual `trim_matches('"')`

converters/html/Cargo.toml

@@ -10,8 +10,8 @@ publish = false
 default = ["pre-spec-subs"]
 # Asciidoctor-compatible subs= attribute. Experimental - may be removed when AsciiDoc spec finalizes.
 pre-spec-subs = ["acdc-parser/pre-spec-subs", "acdc-converters-core/pre-spec-subs"]
-# Enable syntax highlighting for source blocks using syntect
-highlighting = ["dep:syntect"]
+# Enable syntax highlighting for source blocks using giallo
+highlighting = ["dep:giallo"]
 # Render terminal-converter output into selectable HTML via libghostty-vt.
 terminal = ["dep:acdc-converters-terminal", "acdc-converters-terminal/emulator", "acdc-converters-terminal/highlighting"]
 
@@ -20,7 +20,7 @@ acdc-converters-core.workspace = true
 acdc-converters-terminal = { workspace = true, optional = true }
 acdc-parser.workspace = true
 chrono.workspace = true
-syntect = { version = "5.3", optional = true, default-features = false, features = ["default-fancy"] }
+giallo = { git = "https://github.com/getzola/giallo.git", branch = "fancy-regex", optional = true, features = ["dump"] }
 thiserror.workspace = true
 tracing.workspace = true
 

converters/html/README.adoc

@@ -72,7 +72,7 @@ Table of contents entries are also numbered when `:sectnums:` is set.
 
 === Syntax Highlighting
 
-Source blocks with a language specified render with syntax highlighting (requires the `highlighting` feature flag). Uses syntect with inline CSS styles.
+Source blocks with a language specified render with syntax highlighting (requires the `highlighting` feature flag). The converter uses giallo and emits inline CSS styles by default. Set `:highlight-style:` to choose a giallo theme, or `:highlight-css: class` to emit reusable `syntax-*` classes instead. The legacy `:syntect-style:` and `:syntect-css:` names remain accepted for compatibility.
 
 [source,console]
 ....
@@ -347,7 +347,7 @@ server-side, to keep that input away from the emulator.
 
 ==== Syntax highlighting CSS
 
-When using class-based syntax highlighting (`:syntect-css: class`), the highlighting CSS is handled the same way, embedded by default, or linked/written to disk when `:linkcss:` is set. See the <<Syntax Highlighting>> section above.
+When using class-based syntax highlighting (`:highlight-css: class`), the highlighting CSS is handled the same way, embedded by default, or linked/written to disk when `:linkcss:` is set. See the <<Syntax Highlighting>> section above.
 
 === Docinfo files
 
@@ -453,7 +453,7 @@ Most output is class-based and fully overridable by the seams above. A few eleme
 |===
 | Inline-styled | How to override
 
-| Syntax-highlighted code colours | Inline is the default; set `:syntect-css: class` to emit overridable `syntax-*` classes (plus a `<style>` block) instead.
+| Syntax-highlighted code colours | Inline is the default; set `:highlight-css: class` to emit overridable `syntax-*` classes (plus a `<style>` block) instead.
 | A recording's own colours | The cell palette, plus a replay container's background/foreground when the cast recorded a theme; use `!important`.
 | Table column and table widths | Per-table values (matches Asciidoctor); use `!important`.
 | Page break; image `align`/`float` (semantic backend) | Match Asciidoctor's output; use `!important`.
@@ -739,5 +739,5 @@ The HTML converter:
 While the HTML converter aims for compatibility with Asciidoctor, there are some known differences and limitations.
 
 - The `css-signature` attribute is not supported. Use a document ID instead (`[[my-id]]` above the title).
-- Syntax highlighting uses syntect with inline CSS styles rather than external highlight.js or Pygments. Language coverage may differ.
+- Syntax highlighting uses giallo with inline CSS styles rather than external highlight.js or Pygments. Language coverage may differ.
 - The `html5s` backend is inspired by Jakub Jirutka's https://github.com/jirutka/asciidoctor-html5s[asciidoctor-html5s] gem but is a separate implementation with its own output.

converters/html/src/html_visitor.rs

@@ -194,7 +194,7 @@ impl<'a, 'd, W: Write> HtmlVisitor<'a, 'd, W> {
     /// Emit syntax highlighting CSS in `<head>` when class-based mode is active.
     ///
     /// - Without `linkcss`: embeds CSS in a `<style>` block (default).
-    /// - With `linkcss`: emits a `<link>` to `{stylesdir}/acdc-syntect.css`.
+    /// - With `linkcss`: emits a `<link>` to `{stylesdir}/acdc-highlight.css`.
     #[cfg(feature = "highlighting")]
     fn maybe_emit_syntax_css(&mut self) -> Result<(), Error> {
         if self
@@ -218,7 +218,7 @@ impl<'a, 'd, W: Write> HtmlVisitor<'a, 'd, W> {
                         self.writer,
                         r#"<link rel="stylesheet" href="{}/{}">"#,
                         stylesdir.trim_end_matches('/'),
-                        crate::SYNTECT_STYLESHEET
+                        crate::HIGHLIGHT_STYLESHEET
                     )?;
                 } else if let Ok(css) = crate::syntax::highlight_css(&theme_name) {
                     writeln!(self.writer, "<style>\n{css}</style>")?;

converters/html/src/lib.rs

@@ -422,10 +422,10 @@ pub struct RenderOptions {
 pub(crate) const COPYCSS_DEFAULT: &str = "";
 pub(crate) const STYLESDIR_DEFAULT: &str = ".";
 pub(crate) const STYLESHEET_DEFAULT: &str = "";
-/// Default filename for the syntect syntax highlighting stylesheet (class-based mode).
+/// Default filename for the syntax highlighting stylesheet (class-based mode).
 /// Analogous to asciidoctor's `asciidoctor-coderay.css` / `asciidoctor-pygments.css`.
 #[cfg(feature = "highlighting")]
-pub(crate) const SYNTECT_STYLESHEET: &str = "acdc-syntect.css";
+pub(crate) const HIGHLIGHT_STYLESHEET: &str = "acdc-highlight.css";
 // NOTE: If you change the values below, you need to also change them in `load_css`
 pub(crate) const STYLESHEET_LIGHT_MODE: &str = "asciidoctor-light-mode.css";
 pub(crate) const STYLESHEET_DARK_MODE: &str = "asciidoctor-dark-mode.css";
@@ -459,8 +459,10 @@ pub(crate) fn load_css(dark_mode: bool, variant: HtmlVariant) -> &'static str {
 
 /// Resolve the syntax highlighting theme name and mode from document attributes.
 ///
-/// - `:syntect-style:` overrides the theme (falls back to light/dark default).
-/// - `:syntect-css: class` switches to CSS-class mode (default is inline).
+/// - `:highlight-style:` (or legacy `:syntect-style:`) overrides the theme
+///   (falls back to light/dark default).
+/// - `:highlight-css: class` (or legacy `:syntect-css: class`) switches to
+///   CSS-class mode (default is inline).
 #[cfg(feature = "highlighting")]
 pub(crate) fn resolve_highlight_settings(
     document_attributes: &DocumentAttributes<'_>,
@@ -470,7 +472,8 @@ pub(crate) fn resolve_highlight_settings(
         .is_some_and(|v| !matches!(v, AttributeValue::Bool(false) | AttributeValue::None));
 
     let theme_name: String = document_attributes
-        .get("syntect-style")
+        .get("highlight-style")
+        .or_else(|| document_attributes.get("syntect-style"))
         .and_then(|v| match v {
             AttributeValue::String(s) if !s.is_empty() => Some(s.to_string()),
             AttributeValue::String(_) | AttributeValue::Bool(_) | AttributeValue::None | _ => None,
@@ -484,7 +487,8 @@ pub(crate) fn resolve_highlight_settings(
         });
 
     let mode = if document_attributes
-        .get("syntect-css")
+        .get("highlight-css")
+        .or_else(|| document_attributes.get("syntect-css"))
         .is_some_and(|v| matches!(v, AttributeValue::String(s) if s == "class"))
     {
         syntax::HighlightMode::Class
@@ -762,8 +766,8 @@ impl<'a> Processor<'a> {
         }
     }
 
-    /// Write the syntect CSS file next to the HTML output when `linkcss` is set
-    /// and class-based syntax highlighting is active.
+    /// Write the syntax highlighting CSS file next to the HTML output when
+    /// `linkcss` is set and class-based syntax highlighting is active.
     ///
     /// Analogous to how asciidoctor writes `asciidoctor-coderay.css` /
     /// `asciidoctor-pygments.css` alongside the output.
@@ -811,7 +815,7 @@ impl<'a> Processor<'a> {
             output_dir.join(&stylesdir)
         };
 
-        let dest_path = dest_dir.join(SYNTECT_STYLESHEET);
+        let dest_path = dest_dir.join(HIGHLIGHT_STYLESHEET);
 
         if let Err(e) = std::fs::create_dir_all(&dest_dir) {
             diagnostics.warn_with_advice(