feat: add tree-sitter syntax highlighting module

- Cargo.toml: Add tree-sitter-highlight + grammar crates
  (rust, bash, json). TOML dropped due to API incompatibility.
- src/highlight.rs: Language enum, highlight_code() function,
  4 unit tests covering parsing and HTML generation.
- Uses static HTML_ATTRS array for zero-allocation rendering.

Cargo.lock

@@ -14,6 +14,15 @@ dependencies = [
  "zerocopy",
 ]
 
+[[package]]
+name = "aho-corasick"
+version = "1.1.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ddd31a130427c27518df266943a5308ed92d4b226cc639f5a8f1002816174301"
+dependencies = [
+ "memchr",
+]
+
 [[package]]
 name = "allocator-api2"
 version = "0.2.21"
@@ -32,6 +41,16 @@ version = "2.10.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "812e12b5285cc515a9c72a5c1d3b6d46a19dac5acfef5265968c166106e31dd3"
 
+[[package]]
+name = "cc"
+version = "1.2.54"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6354c81bbfd62d9cfa9cb3c773c2b7b2a3a482d569de977fd0e961f6e7c00583"
+dependencies = [
+ "find-msvc-tools",
+ "shlex",
+]
+
 [[package]]
 name = "cfg-if"
 version = "1.0.4"
@@ -47,6 +66,12 @@ dependencies = [
  "cfg-if",
 ]
 
+[[package]]
+name = "find-msvc-tools"
+version = "0.1.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8591b0bcc8a98a64310a2fae1bb3e9b8564dd10e381e6e28010fde8e8e8568db"
+
 [[package]]
 name = "getopts"
 version = "0.2.24"
@@ -93,6 +118,12 @@ version = "1.0.17"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "92ecc6618181def0457392ccd0ee51198e065e016d1d527a7ac1b6dc7c1f09d2"
 
+[[package]]
+name = "lazy_static"
+version = "1.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bbd2bcb4c963f2ddae06a2efc7e9f3591312473c50c6685e1f298068316e66fe"
+
 [[package]]
 name = "maud"
 version = "0.26.0"
@@ -128,7 +159,11 @@ dependencies = [
  "gray_matter",
  "maud",
  "pulldown-cmark",
- "thiserror",
+ "thiserror 2.0.18",
+ "tree-sitter-bash",
+ "tree-sitter-highlight",
+ "tree-sitter-json",
+ "tree-sitter-rust",
  "walkdir",
 ]
 
@@ -198,6 +233,35 @@ dependencies = [
  "proc-macro2",
 ]
 
+[[package]]
+name = "regex"
+version = "1.12.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "843bc0191f75f3e22651ae5f1e72939ab2f72a4bc30fa80a066bd66edefc24d4"
+dependencies = [
+ "aho-corasick",
+ "memchr",
+ "regex-automata",
+ "regex-syntax",
+]
+
+[[package]]
+name = "regex-automata"
+version = "0.4.13"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5276caf25ac86c8d810222b3dbb938e512c55c6831a10f3e6ed1c93b84041f1c"
+dependencies = [
+ "aho-corasick",
+ "memchr",
+ "regex-syntax",
+]
+
+[[package]]
+name = "regex-syntax"
+version = "0.8.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7a2d987857b319362043e95f5353c0535c1f58eec5336fdfcf626430af7def58"
+
 [[package]]
 name = "same-file"
 version = "1.0.6"
@@ -250,6 +314,18 @@ dependencies = [
  "zmij",
 ]
 
+[[package]]
+name = "shlex"
+version = "1.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0fda2ff0d084019ba4d7c6f371c95d8fd75ce3524c3cb8fb653a3023f6323e64"
+
+[[package]]
+name = "streaming-iterator"
+version = "0.1.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2b2231b7c3057d5e4ad0156fb3dc807d900806020c5ffa3ee6ff2c8c76fb8520"
+
 [[package]]
 name = "syn"
 version = "2.0.114"
@@ -261,13 +337,33 @@ dependencies = [
  "unicode-ident",
 ]
 
+[[package]]
+name = "thiserror"
+version = "1.0.69"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b6aaf5339b578ea85b50e080feb250a3e8ae8cfcdff9a461c9ec2904bc923f52"
+dependencies = [
+ "thiserror-impl 1.0.69",
+]
+
 [[package]]
 name = "thiserror"
 version = "2.0.18"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "4288b5bcbc7920c07a1149a35cf9590a2aa808e0bc1eafaade0b80947865fbc4"
 dependencies = [
- "thiserror-impl",
+ "thiserror-impl 2.0.18",
+]
+
+[[package]]
+name = "thiserror-impl"
+version = "1.0.69"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4fee6c4efc90059e10f81e6d42c60a18f76588c3d74cb83a0b242a2b6c7504c1"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
 ]
 
 [[package]]
@@ -290,6 +386,68 @@ dependencies = [
  "serde",
 ]
 
+[[package]]
+name = "tree-sitter"
+version = "0.24.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a5387dffa7ffc7d2dae12b50c6f7aab8ff79d6210147c6613561fc3d474c6f75"
+dependencies = [
+ "cc",
+ "regex",
+ "regex-syntax",
+ "streaming-iterator",
+ "tree-sitter-language",
+]
+
+[[package]]
+name = "tree-sitter-bash"
+version = "0.23.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "329a4d48623ac337d42b1df84e81a1c9dbb2946907c102ca72db158c1964a52e"
+dependencies = [
+ "cc",
+ "tree-sitter-language",
+]
+
+[[package]]
+name = "tree-sitter-highlight"
+version = "0.24.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6411813e4a9ebc87d391b98b0f3ce65d5361cd80c54de8651d8b85b555ea5d95"
+dependencies = [
+ "lazy_static",
+ "regex",
+ "streaming-iterator",
+ "thiserror 1.0.69",
+ "tree-sitter",
+]
+
+[[package]]
+name = "tree-sitter-json"
+version = "0.24.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4d727acca406c0020cffc6cf35516764f36c8e3dc4408e5ebe2cb35a947ec471"
+dependencies = [
+ "cc",
+ "tree-sitter-language",
+]
+
+[[package]]
+name = "tree-sitter-language"
+version = "0.1.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4ae62f7eae5eb549c71b76658648b72cc6111f2d87d24a1e31fa907f4943e3ce"
+
+[[package]]
+name = "tree-sitter-rust"
+version = "0.23.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ca8ccb3e3a3495c8a943f6c3fd24c3804c471fd7f4f16087623c7fa4c0068e8a"
+dependencies = [
+ "cc",
+ "tree-sitter-language",
+]
+
 [[package]]
 name = "unicase"
 version = "2.9.0"

Cargo.toml

@@ -11,3 +11,9 @@ maud           = "0.26"
 pulldown-cmark = "0.12"
 thiserror      = "2"
 walkdir        = "2"
+
+# Syntax highlighting
+tree-sitter-bash      = "0.23"
+tree-sitter-highlight = "0.24"
+tree-sitter-json      = "0.24"
+tree-sitter-rust      = "0.23"

src/highlight.rs

@@ -0,0 +1,172 @@
+//! Syntax highlighting via tree-sitter.
+
+use tree_sitter_highlight::{HighlightConfiguration, Highlighter as TSHighlighter, HtmlRenderer};
+
+/// Recognized highlight names mapped to CSS classes.
+/// Order matters: index becomes the class name suffix.
+const HIGHLIGHT_NAMES: &[&str] = &[
+    "attribute",
+    "comment",
+    "constant",
+    "constant.builtin",
+    "constructor",
+    "function",
+    "function.builtin",
+    "keyword",
+    "number",
+    "operator",
+    "property",
+    "punctuation",
+    "punctuation.bracket",
+    "punctuation.delimiter",
+    "string",
+    "type",
+    "type.builtin",
+    "variable",
+    "variable.builtin",
+    "variable.parameter",
+];
+
+/// Static HTML attributes for each highlight class.
+/// Pre-computed to avoid allocations in the render loop.
+const HTML_ATTRS: &[&[u8]] = &[
+    b"<span class=\"hl-attribute\">",
+    b"<span class=\"hl-comment\">",
+    b"<span class=\"hl-constant\">",
+    b"<span class=\"hl-constant-builtin\">",
+    b"<span class=\"hl-constructor\">",
+    b"<span class=\"hl-function\">",
+    b"<span class=\"hl-function-builtin\">",
+    b"<span class=\"hl-keyword\">",
+    b"<span class=\"hl-number\">",
+    b"<span class=\"hl-operator\">",
+    b"<span class=\"hl-property\">",
+    b"<span class=\"hl-punctuation\">",
+    b"<span class=\"hl-punctuation-bracket\">",
+    b"<span class=\"hl-punctuation-delimiter\">",
+    b"<span class=\"hl-string\">",
+    b"<span class=\"hl-type\">",
+    b"<span class=\"hl-type-builtin\">",
+    b"<span class=\"hl-variable\">",
+    b"<span class=\"hl-variable-builtin\">",
+    b"<span class=\"hl-variable-parameter\">",
+];
+
+/// Supported languages for syntax highlighting.
+#[derive(Debug, Clone, Copy, PartialEq)]
+pub enum Language {
+    Rust,
+    Bash,
+    Json,
+}
+
+impl Language {
+    /// Parse a language identifier from a code fence.
+    pub fn from_fence(lang: &str) -> Option<Self> {
+        match lang.to_lowercase().as_str() {
+            "rust" | "rs" => Some(Language::Rust),
+            "bash" | "sh" | "shell" | "zsh" => Some(Language::Bash),
+            "json" => Some(Language::Json),
+            _ => None,
+        }
+    }
+}
+
+/// Get highlight configuration for a language.
+fn get_config(lang: Language) -> HighlightConfiguration {
+    let (language, name, highlights) = match lang {
+        Language::Rust => (
+            tree_sitter_rust::LANGUAGE.into(),
+            "rust",
+            tree_sitter_rust::HIGHLIGHTS_QUERY,
+        ),
+        Language::Bash => (
+            tree_sitter_bash::LANGUAGE.into(),
+            "bash",
+            tree_sitter_bash::HIGHLIGHT_QUERY,
+        ),
+        Language::Json => (
+            tree_sitter_json::LANGUAGE.into(),
+            "json",
+            tree_sitter_json::HIGHLIGHTS_QUERY,
+        ),
+    };
+
+    let mut config = HighlightConfiguration::new(language, name, highlights, "", "")
+        .expect("highlight query should be valid");
+
+    config.configure(HIGHLIGHT_NAMES);
+    config
+}
+
+/// Highlight source code and return HTML with span elements.
+pub fn highlight_code(lang: Language, source: &str) -> String {
+    let mut highlighter = TSHighlighter::new();
+    let config = get_config(lang);
+
+    let highlights = match highlighter.highlight(&config, source.as_bytes(), None, |_| None) {
+        Ok(h) => h,
+        Err(_) => return html_escape(source),
+    };
+
+    let mut renderer = HtmlRenderer::new();
+    let result = renderer.render(highlights, source.as_bytes(), &|highlight| {
+        HTML_ATTRS.get(highlight.0).copied().unwrap_or(b"<span>")
+    });
+
+    match result {
+        Ok(()) => String::from_utf8_lossy(&renderer.html).into_owned(),
+        Err(_) => html_escape(source),
+    }
+}
+
+/// Simple HTML escape for fallback.
+fn html_escape(s: &str) -> String {
+    s.replace('&', "&amp;")
+        .replace('<', "&lt;")
+        .replace('>', "&gt;")
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_language_from_fence() {
+        assert_eq!(Language::from_fence("rust"), Some(Language::Rust));
+        assert_eq!(Language::from_fence("rs"), Some(Language::Rust));
+        assert_eq!(Language::from_fence("bash"), Some(Language::Bash));
+        assert_eq!(Language::from_fence("sh"), Some(Language::Bash));
+        assert_eq!(Language::from_fence("json"), Some(Language::Json));
+        assert_eq!(Language::from_fence("unknown"), None);
+    }
+
+    #[test]
+    fn test_highlight_rust_code() {
+        let code = "fn main() { println!(\"hello\"); }";
+        let html = highlight_code(Language::Rust, code);
+
+        // Should contain span elements with highlight classes
+        assert!(html.contains("<span class=\"hl-"));
+        // Should contain the keyword "fn"
+        assert!(html.contains("fn"));
+        // Should contain the string
+        assert!(html.contains("hello"));
+    }
+
+    #[test]
+    fn test_highlight_bash_code() {
+        let code = "#!/bin/bash\necho \"hello world\"";
+        let html = highlight_code(Language::Bash, code);
+
+        assert!(html.contains("<span class=\"hl-"));
+        assert!(html.contains("echo"));
+    }
+
+    #[test]
+    fn test_html_escape_fallback() {
+        let escaped = html_escape("<script>alert('xss')</script>");
+        assert!(!escaped.contains('<'));
+        assert!(escaped.contains("&lt;"));
+    }
+}

src/main.rs

@@ -4,6 +4,7 @@
 
 mod content;
 mod error;
+mod highlight;
 mod render;
 mod templates;