wip: lockfile

wip

wip: candidate

crates/core/Cargo.toml

@@ -0,0 +1,27 @@
+[package]
+name = "tailwindcss-core"
+version = "0.1.0"
+edition = "2021"
+
+[lib]
+crate-type = ["cdylib"]
+
+[profile.release]
+lto = true
+opt-level = "s"
+panic = "abort"
+strip = true
+codegen-units = 1
+
+[dependencies]
+serde_json = "1.0.127"
+log = "0.4.22"
+wasm-bindgen = "0.2.93"
+bstr = "1.10.0"
+memmem = "0.1.1"
+memchr = "2.7.4"
+tinyvec = { version = "1.8.0", features = ["alloc"] }
+
+[dev-dependencies]
+rstest = "0.22.0"
+rstest_reuse = "0.7.0"

crates/core/src/compat/config.rs

@@ -0,0 +1,5 @@
+use serde_json::Value;
+
+pub struct UserConfig {
+  internal: Value,
+}

crates/core/src/compat/mod.rs

@@ -0,0 +1 @@
+pub mod config;

crates/core/src/compat/plugin.rs

@@ -0,0 +1,7 @@
+pub struct Plugin {
+  /// An internal identifier that the server uses to identify the plugin.
+  /// This identifier is guaranteed to be unique for the lifetime of the
+  /// plugin server but is not guaranteed to be unique across multiple
+  /// invocations of the server.
+  handle: u64
+}

crates/core/src/compiler.rs

@@ -0,0 +1,18 @@
+use std::error::Error;
+
+use crate::css::parser::parse;
+use crate::css::ast::Stylesheet;
+
+struct Compiler {
+  ast: Stylesheet,
+}
+
+impl Compiler {
+  fn new(css: &[u8]) -> Result<Compiler, Box<dyn Error>> {
+    let ast = parse(css)?;
+
+    Ok(Compiler {
+      ast,
+    })
+  }
+}

crates/core/src/css/ast.rs

@@ -0,0 +1,156 @@
+use std::{collections::HashMap, fmt, unreachable};
+
+/// Represents the AST of a CSS stylesheet
+#[derive(Clone, PartialEq)]
+pub struct Stylesheet {
+  pub(crate) rules: CssNode,
+}
+
+/// A node in a CSS Stylesheet
+#[derive(Clone, PartialEq)]
+pub enum CssNode {
+  /// A context block used to provide shared data to subtrees
+  Context {
+    data: HashMap<String, String>,
+    nodes: Vec<CssNode>,
+  },
+
+  /// A CSS at rule
+  AtRule {
+    name: Vec<u8>,
+    params: Vec<u8>,
+    nodes: Vec<CssNode>,
+  },
+
+  /// A CSS style rule
+  StyleRule {
+    selector: Vec<u8>,
+    nodes: Vec<CssNode>,
+  },
+
+  /// A CSS declaration
+  Declaration {
+    property: Vec<u8>,
+    value: Vec<u8>,
+    important: bool,
+  },
+
+  /// A comment
+  Comment {
+    value: Vec<u8>,
+  },
+
+  /// Represents multiple CSS nodes
+  /// This is used when replacing a single node with multiple nodes
+  Contents {
+    nodes: Vec<CssNode>,
+  },
+}
+
+pub fn style_rule(selector: impl Into<Vec<u8>>, nodes: impl Into<Vec<CssNode>>) -> CssNode {
+  CssNode::StyleRule {
+    selector: selector.into(),
+    nodes: nodes.into(),
+  }
+}
+
+pub fn at_rule(name: impl Into<Vec<u8>>, params: impl Into<Vec<u8>>, nodes: impl Into<Vec<CssNode>>) -> CssNode {
+  CssNode::AtRule {
+    name: name.into(),
+    params: params.into(),
+    nodes: nodes.into()
+  }
+}
+
+
+pub fn decl(property: impl Into<Vec<u8>>, value: impl Into<Vec<u8>>, important: bool) -> CssNode {
+  CssNode::Declaration {
+    property: property.into(),
+    value: value.into(),
+    important,
+  }
+}
+
+pub fn comment(value: impl Into<Vec<u8>>) -> CssNode {
+  CssNode::Comment { value: value.into() }
+}
+
+impl<T> From<T> for CssNode where T: Into<Vec<CssNode>> {
+  fn from(nodes: T) -> Self {
+    CssNode::Contents { nodes: nodes.into() }
+  }
+}
+
+impl<T> From<T> for Stylesheet where T: Into<Vec<CssNode>> {
+  fn from(nodes: T) -> Self {
+    Stylesheet {
+      rules: CssNode::from(nodes.into())
+    }
+  }
+}
+
+impl CssNode {
+  pub fn empty() -> Self {
+    CssNode::from([])
+  }
+}
+
+impl fmt::Debug for Stylesheet {
+  fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+    write!(f, "Stylesheet {{ rules: {:?} }}", self.rules)
+  }
+}
+
+impl fmt::Debug for CssNode {
+  fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+    match self {
+      CssNode::Context { data, nodes } => {
+        write!(f, "Context {{ data: {:?}, nodes: {:?} }}", data, nodes)
+      },
+
+      CssNode::AtRule { name, params, nodes } => {
+        write!(f, "AtRule {{ name: {:?}, params: {:?}, nodes: {:?} }}", String::from_utf8_lossy(name), String::from_utf8_lossy(params), nodes)
+      },
+
+      CssNode::StyleRule { selector, nodes } => {
+        write!(f, "StyleRule {{ selector: {:?}, nodes: {:?} }}", String::from_utf8_lossy(selector), nodes)
+      },
+
+      CssNode::Declaration { property, value, important } => {
+        write!(f, "Declaration {{ property: {:?}, value: {:?}, important: {:?} }}", String::from_utf8_lossy(property), String::from_utf8_lossy(value), important)
+      },
+
+      CssNode::Comment { value } => {
+        write!(f, "Comment {{ value: {:?} }}", String::from_utf8_lossy(value))
+      },
+
+      CssNode::Contents { nodes } => {
+        write!(f, "Contents {{ nodes: {:?} }}", nodes)
+      },
+    }
+  }
+}
+
+impl CssNode {
+  #[inline(always)]
+  pub fn push(&mut self, node: CssNode) {
+    match self {
+      CssNode::AtRule { nodes, .. } => {
+        nodes.push(node);
+      },
+      CssNode::StyleRule { nodes, .. } => {
+        nodes.push(node);
+      },
+      CssNode::Contents { nodes, .. } => {
+        nodes.push(node);
+      },
+      _ => {
+        if cfg!(debug_assertions) {
+          panic!("Cannot push to a non-container node.");
+        } else {
+          unreachable!();
+        }
+      }
+    }
+  }
+}

crates/core/src/css/mod.rs

@@ -0,0 +1,6 @@
+pub mod ast;
+pub mod optimize;
+pub mod parser;
+pub mod serializer;
+pub mod syntax;
+pub mod visit;

crates/core/src/css/optimize.rs

@@ -0,0 +1,306 @@
+// Performs an optimization pass on the AST to (usually) reduce the size of the output CSS
+
+use std::{collections::HashSet, mem};
+
+use super::{ast::{at_rule, decl, style_rule, CssNode, Stylesheet}, visit::WalkAction};
+
+pub fn optimize_ast(ast: &mut Stylesheet) {
+  remove_duplicate_at_properties(ast);
+  add_property_fallbacks(ast);
+  hoist_at_roots(ast);
+  flatten_utilities(ast);
+}
+
+/// Remove duplicate `@property` rules appearing in the AST
+/// They're replaced with empty nodes that print nothing
+fn remove_duplicate_at_properties(ast: &mut Stylesheet) {
+  let mut seen = HashSet::<Vec<u8>>::new();
+
+  ast.walk_mut(&mut |node| {
+    let CssNode::AtRule { name, params, .. } = node else {
+      return WalkAction::Continue;
+    };
+
+    if name != b"property" {
+      return WalkAction::Continue;
+    }
+
+    if !seen.contains(params) {
+      seen.insert(params.clone());
+
+      return WalkAction::Continue;
+    }
+
+    *node = CssNode::empty();
+
+    return WalkAction::Skip;
+  })
+}
+
+/// Collect fallbacks for `@property` rules for Firefox support
+/// We turn these into rules on `:root` or `*` and some pseudo-elements
+/// based on the value of `inherits`
+fn add_property_fallbacks(ast: &mut Stylesheet) {
+  let mut fallbacks_root = Vec::<CssNode>::new();
+  let mut fallbacks_universal = Vec::<CssNode>::new();
+
+  // Create fallback rules for defined properties
+  ast.walk_mut(&mut |node| {
+    let CssNode::AtRule { name, params, nodes, .. } = node else {
+      return WalkAction::Continue;
+    };
+
+    if name != b"property" {
+      return WalkAction::Continue;
+    }
+
+    let property_name = params.clone();
+    let mut initial_value: Option<Vec<u8>> = None;
+    let mut inherits = false;
+
+    for child in nodes {
+      let CssNode::Declaration { property, value, .. } = child else {
+        continue;
+      };
+
+      if property == b"initial-value" {
+        initial_value = Some(value.clone());
+      } else if property == b"inherits" {
+        inherits = value == b"true";
+      }
+    }
+
+    let initial_value = initial_value.unwrap_or(b"initial".to_vec());
+
+    if inherits {
+      fallbacks_root.push(decl(property_name, initial_value, false));
+    } else {
+      fallbacks_universal.push(decl(property_name, initial_value, false));
+    }
+
+    return WalkAction::Skip;
+  });
+
+  let CssNode::Contents { nodes } = &mut ast.rules else {
+    return;
+  };
+
+  let mut fallback_ast = vec![];
+
+  if !fallbacks_root.is_empty() {
+    fallback_ast.push(style_rule(b":root", fallbacks_root));
+  }
+
+  if !fallbacks_universal.is_empty() {
+    fallback_ast.push(style_rule(
+      b"*, ::before, ::after, ::backdrop",
+      fallbacks_universal
+    ));
+  }
+
+  if !fallback_ast.is_empty() {
+    fallback_ast = vec![
+      at_rule(b"supports", b"(-moz-orient: inline)", [
+        at_rule(b"layer", b"base", fallback_ast),
+      ]),
+    ];
+  }
+
+  nodes.extend(fallback_ast);
+}
+
+/// Collect fallbacks for `@property` rules for Firefox support
+/// We turn these into rules on `:root` or `*` and some pseudo-elements
+/// based on the value of `inherits`
+fn hoist_at_roots(ast: &mut Stylesheet) {
+  let mut roots = Vec::<CssNode>::new();
+
+  ast.walk_mut(&mut |node| {
+    let CssNode::AtRule { name, nodes, .. } = node else {
+      return WalkAction::Continue;
+    };
+
+    if name != b"at-root" {
+      return WalkAction::Continue;
+    }
+
+    // Pull the nodes out of the at-root rule
+    roots.extend(mem::take(nodes));
+
+    // Replace the at-root rule with an empty node
+    *node = CssNode::empty();
+
+    return WalkAction::Skip;
+  });
+
+  let CssNode::Contents { nodes } = &mut ast.rules else {
+    return;
+  };
+
+  nodes.extend(roots);
+}
+
+/// Collect fallbacks for `@property` rules for Firefox support
+/// We turn these into rules on `:root` or `*` and some pseudo-elements
+/// based on the value of `inherits`
+fn flatten_utilities(ast: &mut Stylesheet) {
+  ast.walk_mut(&mut |node| {
+    let CssNode::AtRule { name, params, nodes, .. } = node else {
+      return WalkAction::Continue;
+    };
+
+    if name != b"tailwind" {
+      return WalkAction::Continue;
+    }
+
+    if params != b"utilities" {
+      return WalkAction::Continue;
+    }
+
+    *node = CssNode::from(mem::take(nodes));
+
+    return WalkAction::Skip;
+  });
+}
+
+#[cfg(test)]
+mod tests {
+  use super::*;
+
+  #[test]
+  fn test_remove_duplicate_at_properties() {
+    let mut css = Stylesheet::from([
+      at_rule("property", "--foo", [
+        decl("syntax", "<length>", false),
+        decl("inherits", "false", false),
+        decl("initial-value", "0", false),
+      ]),
+
+      at_rule("property", "--foo", [
+        decl("syntax", "<length>", false),
+        decl("inherits", "false", false),
+        decl("initial-value", "0", false),
+      ]),
+    ]);
+
+    remove_duplicate_at_properties(&mut css);
+
+    let expected = Stylesheet::from([
+      at_rule("property", "--foo", [
+        decl("syntax", "<length>", false),
+        decl("inherits", "false", false),
+        decl("initial-value", "0", false),
+      ]),
+
+      CssNode::empty(),
+    ]);
+
+    assert_eq!(css, expected);
+  }
+
+  #[test]
+  fn test_add_property_fallbacks() {
+    let mut css = Stylesheet::from([
+      at_rule("property", "--foo", [
+        decl("syntax", "<length>", false),
+        decl("inherits", "true", false),
+        decl("initial-value", "0", false),
+      ]),
+
+      at_rule("property", "--bar", [
+        decl("syntax", "<length>", false),
+        decl("inherits", "false", false),
+        decl("initial-value", "0", false),
+      ]),
+    ]);
+
+    add_property_fallbacks(&mut css);
+
+    let expected = Stylesheet::from([
+      at_rule("property", "--foo", [
+        decl("syntax", "<length>", false),
+        decl("inherits", "true", false),
+        decl("initial-value", "0", false),
+      ]),
+
+      at_rule("property", "--bar", [
+        decl("syntax", "<length>", false),
+        decl("inherits", "false", false),
+        decl("initial-value", "0", false),
+      ]),
+
+      at_rule("supports", "(-moz-orient: inline)", [
+        at_rule("layer", "base", [
+          style_rule(":root", [
+            decl("--foo", "0", false),
+          ]),
+
+          style_rule("*, ::before, ::after, ::backdrop", [
+            decl("--bar", "0", false),
+          ]),
+        ]),
+      ]),
+    ]);
+
+    assert_eq!(css, expected);
+  }
+
+  #[test]
+  fn test_hoist_at_roots() {
+    let mut css = Stylesheet::from([
+      at_rule("layer", "base", [
+        at_rule("at-root", "", [
+          at_rule("keyframes", "spin", [
+            style_rule("from", [
+              decl("transform", "rotate(0deg)", false),
+            ]),
+
+            style_rule("to", [
+              decl("transform", "rotate(360deg)", false),
+            ]),
+          ]),
+        ]),
+
+        at_rule("layer", "defaults", [
+          at_rule("at-root", "", [
+            at_rule("keyframes", "pulse", [
+              style_rule("50%", [
+                decl("opacity", "0", false),
+              ]),
+            ]),
+          ]),
+        ]),
+      ])
+    ]);
+
+    hoist_at_roots(&mut css);
+
+    let expected = Stylesheet::from([
+      at_rule("layer", "base", [
+        CssNode::empty(),
+
+        at_rule("layer", "defaults", [
+          CssNode::empty(),
+        ]),
+      ]),
+
+      at_rule("keyframes", "spin", [
+        style_rule("from", [
+          decl("transform", "rotate(0deg)", false),
+        ]),
+
+        style_rule("to", [
+          decl("transform", "rotate(360deg)", false),
+        ]),
+      ]),
+
+      at_rule("keyframes", "pulse", [
+        style_rule("50%", [
+          decl("opacity", "0", false),
+        ]),
+      ]),
+    ]);
+
+    assert_eq!(css, expected);
+  }
+}

crates/core/src/css/serializer.rs

@@ -0,0 +1,159 @@
+use super::ast::{CssNode, Stylesheet};
+
+impl Stylesheet {
+  pub fn to_css(&self) -> Vec<u8> {
+    self.rules.to_css()
+  }
+}
+
+impl CssNode {
+  fn to_css(&self) -> Vec<u8> {
+    let mut css: Vec<u8> = vec![];
+    self.write_css_to(&mut css, 0);
+    return css;
+  }
+
+  fn write_css_to(&self, css: &mut Vec<u8>, depth: usize) {
+    let indent = b"  ".repeat(depth);
+
+    match self {
+      CssNode::Comment { value } => {
+        css.extend(&indent);
+        css.extend(b"/*");
+        css.extend(value);
+        css.extend(b"*/\n");
+      },
+
+      CssNode::Declaration { property, value, important } => {
+        css.extend(&indent);
+        css.extend(property);
+        css.extend(b": ");
+        css.extend(value);
+        if *important {
+          css.extend(b" !important");
+        }
+        css.extend(b";\n");
+      },
+
+      CssNode::Context { nodes, .. } => {
+        for child in nodes {
+          child.write_css_to(css, depth);
+        }
+      },
+
+      CssNode::Contents { nodes } => {
+        for child in nodes {
+          child.write_css_to(css, depth);
+        }
+      },
+
+      CssNode::AtRule { name, params, nodes } => {
+        css.extend(&indent);
+        css.extend(b"@");
+        css.extend(name);
+        css.extend(b" ");
+        css.extend(params);
+
+        // Print at-rules without nodes with a `;` instead of an empty block.
+        //
+        // E.g.:
+        //
+        // ```css
+        // @layer base, components, utilities;
+        // ```
+        if nodes.is_empty() {
+          css.extend(b";\n");
+        } else {
+          css.extend(b" {\n");
+
+          for child in nodes {
+            child.write_css_to(css, depth + 1);
+          }
+
+          css.extend(&indent);
+          css.extend(b"}\n");
+        }
+      },
+
+      CssNode::StyleRule { selector, nodes } => {
+        css.extend(&indent);
+        css.extend(selector);
+        css.extend(b" {\n");
+
+        for child in nodes {
+          child.write_css_to(css, depth + 1);
+        }
+
+        css.extend(&indent);
+        css.extend(b"}\n");
+      }
+    }
+  }
+}
+
+#[cfg(test)]
+mod test {
+  use crate::css::{ast::{comment, decl}, parser::parse};
+
+  #[test]
+  fn should_pretty_print_an_ast() {
+    let css = parse(b".foo{color:red;&:hover{color:blue;}}").unwrap();
+
+    assert_eq!(css.to_css(), b".foo {\n  color: red;\n  &:hover {\n    color: blue;\n  }\n}\n");
+  }
+
+  #[test]
+  fn should_print_decls() {
+    let css = decl(b"color", "red", false);
+    assert_eq!(css.to_css(), b"color: red;\n");
+  }
+
+  #[test]
+  fn should_print_decls_important() {
+    let css = decl(b"color", "red", true);
+    assert_eq!(css.to_css(), b"color: red !important;\n");
+  }
+
+  #[test]
+  fn should_print_comments() {
+    let css = comment(b" hello world ");
+
+    assert_eq!(css.to_css(), b"/* hello world */\n");
+  }
+
+  #[test]
+  fn should_print_at_rules_without_a_body() {
+    let css = parse(b"@layer base, components, utilities;").unwrap();
+    assert_eq!(css.to_css(), b"@layer base, components, utilities;\n");
+  }
+
+  #[test]
+  fn should_print_at_rules_with_a_body() {
+    let css = parse(b"@layer base { color: red; }").unwrap();
+    assert_eq!(css.to_css(), b"@layer base {\n  color: red;\n}\n");
+  }
+
+  #[test]
+  fn should_print_at_rules_with_a_body_and_nested_rules() {
+    let css = parse(b"@layer base { color: red; &:hover { color: blue; } }").unwrap();
+    assert_eq!(css.to_css(), b"@layer base {\n  color: red;\n  &:hover {\n    color: blue;\n  }\n}\n");
+  }
+
+  #[test]
+  fn should_print_style_rules() {
+    let css = parse(b".foo { color: red; }").unwrap();
+    assert_eq!(css.to_css(), b".foo {\n  color: red;\n}\n");
+  }
+
+  #[test]
+  fn should_print_style_rules_with_nested_style_rules() {
+    let css = parse(b".foo { color: red; &:hover { color: blue; } }").unwrap();
+    assert_eq!(css.to_css(), b".foo {\n  color: red;\n  &:hover {\n    color: blue;\n  }\n}\n");
+  }
+
+  #[test]
+  fn should_print_style_rules_with_nested_at_rules() {
+    let css = parse(b".foo { color: red; @layer base { color: blue; } }").unwrap();
+    assert_eq!(css.to_css(), b".foo {\n  color: red;\n  @layer base {\n    color: blue;\n  }\n}\n");
+  }
+}

crates/core/src/css/syntax.rs

@@ -0,0 +1,56 @@
+// The order of these cases is important for performance
+// please do not change it without significant profiling
+#[derive(Copy, Clone)]
+enum Case {
+  Escape,
+  Ident,
+  Other,
+}
+
+const __CASES: [Case; 256] = {
+  let mut table = [Case::Other; 256];
+
+  let mut i = b'a';
+  while i <= b'z' {
+    table[i as usize] = Case::Ident;
+    i+=1;
+  }
+
+  let mut i = b'A';
+  while i <= b'Z' {
+    table[i as usize] = Case::Ident;
+    i+=1;
+  }
+
+  let mut i = b'0';
+  while i <= b'9' {
+    table[i as usize] = Case::Ident;
+    i+=1;
+  }
+
+  table[b'-' as usize] = Case::Ident;
+  table[b'_' as usize] = Case::Ident;
+  table[b'\\' as usize] = Case::Escape;
+
+  table
+};
+
+/// Consume an <ident-token> from the buffer
+///
+/// Not intended to be as strict as the [CSS spec][diagram] but merely good enough.
+/// [diagram]: https://drafts.csswg.org/css-syntax-3/#ident-token-diagram
+#[inline(never)]
+#[no_mangle]
+pub fn read_ident_token(buffer: &[u8]) -> usize {
+  let mut i = 0;
+
+  while i < buffer.len() {
+    match __CASES[buffer[i] as usize] {
+      Case::Ident => i += 1,
+      Case::Escape => i += 2,
+      Case::Other => break,
+    }
+  }
+
+  return i;
+}

crates/core/src/css/visit.rs

@@ -0,0 +1,192 @@
+use super::ast::{CssNode, Stylesheet};
+
+#[derive(Debug, Clone, PartialEq)]
+pub enum WalkAction {
+  // Continue walking, which is the default
+  Continue,
+
+  // Skip visiting the children of this node
+  Skip,
+
+  // Stop the walk entirely
+  Stop,
+}
+
+impl Stylesheet {
+  pub fn walk<V>(&self, cb: &V)
+  where
+    V: Fn(&CssNode) -> WalkAction
+  {
+    self.rules.walk(cb)
+  }
+}
+
+impl CssNode {
+  pub fn walk<V>(&self, cb: &V)
+  where
+      V: Fn(&CssNode) -> WalkAction
+  {
+    _ = self.walk_impl(cb);
+  }
+
+  fn walk_impl<V>(&self, cb: &V) -> WalkAction
+  where
+      V: Fn(&CssNode) -> WalkAction
+  {
+    match cb(self) {
+      WalkAction::Stop => return WalkAction::Stop,
+      WalkAction::Skip => return WalkAction::Skip,
+      WalkAction::Continue => {}
+    }
+
+    for node in self.children() {
+      match node.walk_impl(cb) {
+        WalkAction::Stop => return WalkAction::Stop,
+        WalkAction::Skip => {}
+        WalkAction::Continue => {}
+      }
+    }
+
+    WalkAction::Continue
+  }
+
+  fn children(&self) -> impl Iterator<Item = &CssNode> {
+    match self {
+      CssNode::Context { nodes, .. } => nodes.iter(),
+      CssNode::AtRule { nodes, .. } => nodes.iter(),
+      CssNode::StyleRule { nodes, .. } => nodes.iter(),
+      CssNode::Contents { nodes, .. } => nodes.iter(),
+      CssNode::Declaration { .. } => [].iter(),
+      CssNode::Comment { .. } => [].iter(),
+    }
+  }
+}
+
+impl Stylesheet {
+  pub fn walk_mut<V>(&mut self, cb: &mut V)
+  where
+    V: FnMut(&mut CssNode) -> WalkAction
+  {
+    self.rules.walk_mut(cb)
+  }
+}
+
+impl CssNode {
+  pub fn walk_mut<V>(&mut self, cb: &mut V)
+  where
+      V: FnMut(&mut CssNode) -> WalkAction
+  {
+    _ = self.walk_mut_impl(cb);
+  }
+
+  fn walk_mut_impl<V>(&mut self, cb: &mut V) -> WalkAction
+  where
+      V: FnMut(&mut CssNode) -> WalkAction
+  {
+    match cb(self) {
+      WalkAction::Stop => return WalkAction::Stop,
+      WalkAction::Skip => return WalkAction::Skip,
+      WalkAction::Continue => {}
+    }
+
+    for node in self.children_mut() {
+      match node.walk_mut_impl(cb) {
+        WalkAction::Stop => return WalkAction::Stop,
+        WalkAction::Skip => {}
+        WalkAction::Continue => {}
+      }
+    }
+
+    WalkAction::Continue
+  }
+
+  pub fn children_mut(&mut self) -> impl Iterator<Item = &mut CssNode> {
+    match self {
+      CssNode::Context { nodes, .. } => nodes.iter_mut(),
+      CssNode::AtRule { nodes, .. } => nodes.iter_mut(),
+      CssNode::StyleRule { nodes, .. } => nodes.iter_mut(),
+      CssNode::Contents { nodes, .. } => nodes.iter_mut(),
+      CssNode::Declaration { .. } => [].iter_mut(),
+      CssNode::Comment { .. } => [].iter_mut(),
+    }
+  }
+}
+
+#[cfg(test)]
+mod test {
+  use super::*;
+  use crate::css::ast::*;
+  use std::cell::Cell;
+
+  #[test]
+  fn test_walk() {
+    let ast = Stylesheet::from([
+      style_rule("h1", [
+        decl("color", "red", false),
+        decl("font-size", "2em", false),
+      ]),
+      style_rule("h2", [
+        decl("color", "blue", false),
+        decl("font-size", "1.5em", false),
+      ]),
+    ]);
+
+    let count = Cell::new(0);
+
+    ast.walk(&|node| {
+      if let CssNode::Declaration { property, .. } = node {
+        if property == b"color" {
+          count.set(count.get() + 1);
+        }
+      }
+
+      WalkAction::Continue
+    });
+
+    assert_eq!(count.get(), 2);
+  }
+
+  #[test]
+  fn test_walk_mut() {
+    let mut ast = Stylesheet::from([
+      style_rule("h1", [
+        decl("color", "red", false),
+        decl("font-size", "2em", false),
+      ]),
+      style_rule("h2", [
+        decl("color", "blue", false),
+        decl("font-size", "1.5em", false),
+      ]),
+    ]);
+
+    // 1. Change all color properties to green
+    ast.walk_mut(&mut |node| {
+      let CssNode::Declaration { property, value, .. } = node else {
+        return WalkAction::Continue;
+      };
+
+      if property != b"color" {
+        return WalkAction::Continue;
+      }
+
+      *value = "green".into();
+
+      return WalkAction::Continue;
+    });
+
+    // 2. Re-walk the AST and check that all color properties are green
+    let count = Cell::new(0);
+
+    ast.walk(&|node| {
+      if let CssNode::Declaration { property, value, .. } = node {
+        if property == b"color" && value == b"green" {
+          count.set(count.get() + 1);
+        }
+      }
+
+      WalkAction::Continue
+    });
+
+    assert_eq!(count.get(), 2);
+  }
+}

crates/core/src/engine/candidate.rs

@@ -0,0 +1,329 @@
+use std::{iter::empty, rc::Rc, sync::Arc};
+use bstr::ByteSlice;
+
+use crate::util::segment;
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct Candidate {
+  raw: Vec<u8>,
+  important: bool,
+  variants: Vec<Variant>,
+  utilities: Vec<Utility>,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum Variant {
+  /// Arbitrary variants are variants that take a selector and generate a variant
+  /// on the fly.
+  ///
+  /// E.g.: `[&_p]`
+  Arbitrary {
+    selector: Vec<u8>,
+
+    /// If true, it can be applied as a child of a compound variant
+    compounds: bool,
+
+    /// Whether or not the selector is a relative selector
+    /// @see https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_selectors/Selector_structure#relative_selector
+    relative: bool,
+  },
+
+  /// Static variants are variants that don't take any arguments.
+  ///
+  /// E.g.: `hover`
+  Static {
+    root: Vec<u8>,
+    compounds: bool,
+  },
+
+  /// Functional variants are variants that can take an argument. The argument is
+  /// either a named variant value or an arbitrary variant value.
+  ///
+  /// E.g.:
+  ///
+  /// - `aria-disabled`
+  /// - `aria-[disabled]`
+  /// - `@container-size`          -> @container, with named value `size`
+  /// - `@container-[inline-size]` -> @container, with arbitrary variant value `inline-size`
+  /// - `@container`               -> @container, with no value
+  Functional {
+    root: Vec<u8>,
+    value: Option<VariantValue>,
+    modifier: Option<CandidateModifier>,
+
+    /// If true, it can be applied as a child of a compound variant
+    compounds: bool,
+  },
+
+  /// Compound variants are variants that take another variant as an argument.
+  ///
+  /// E.g.:
+  ///
+  /// - `has-[&_p]`
+  /// - `group-*`
+  /// - `peer-*`
+  Compound {
+    root: Vec<u8>,
+    variant: Box<Variant>,
+    modifier: Option<CandidateModifier>,
+
+    /// If true, it can be applied as a child of a compound variant
+    compounds: bool,
+  }
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum Utility {
+  /// Arbitrary candidates are candidates that register utilities on the fly with
+  /// a property and a value.
+  ///
+  /// Examples:
+  /// - `[color:red]`
+  /// - `[color:red]/50`
+  /// - `[color:red]/50!`
+  Arbitrary {
+    property: Vec<u8>,
+    value: Vec<u8>,
+    modifier: Option<CandidateModifier>,
+  },
+
+  ///  Static candidates are candidates that don't take any arguments.
+  ///
+  ///  Examples:
+  ///  - `underline`
+  ///  - `flex`
+  Static {
+    root: Vec<u8>,
+  },
+
+  ///  Static candidates are candidates that don't take any arguments.
+  ///
+  ///  Examples:
+  ///  - `underline`
+  ///  - `flex`
+  Functional {
+    root: Vec<u8>,
+    value: Option<UtilityValue>,
+    modifier: Option<CandidateModifier>,
+  }
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum UtilityValue {
+  Arbitrary {
+    /// bg-[color:--my-color]
+    ///     ^^^^^
+    data_type: Option<Vec<u8>>,
+
+    /// bg-[#0088cc]
+    ///     ^^^^^^^
+    /// bg-[var(--my_variable)]
+    ///     ^^^^^^^^^^^^^^^^^^
+    value: Vec<u8>,
+  },
+
+  Named {
+    /// bg-red-500
+    ///    ^^^^^^^
+    ///
+    /// w-1/2
+    ///   ^
+    value: Vec<u8>,
+
+    /// w-1/2
+    ///   ^^^
+    fraction: Option<Vec<u8>>
+  }
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum VariantValue {
+  Arbitrary {
+    value: Vec<u8>,
+  },
+
+  Named {
+    value: Vec<u8>,
+  }
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum CandidateModifier {
+  Arbitrary {
+    /// bg-red-500/[50%]
+    ///             ^^^
+    value: Vec<u8>
+  },
+
+  Named {
+    /// bg-red-500/50
+    ///            ^^
+    value: Vec<u8>,
+  }
+}
+
+pub struct DesignSystem {
+  prefix: Option<Vec<u8>>,
+  utilities: Utilities,
+}
+
+pub struct Utilities {
+  //
+}
+
+impl Utilities {
+  pub fn has(&self, utility: &[u8]) -> bool {
+    false
+  }
+}
+
+pub fn parse_candidate(input: &[u8], design: Rc<DesignSystem>) -> Option<Candidate> {
+  let raw = input.to_vec();
+
+  // hover:focus:underline
+  // ^^^^^ ^^^^^^           -> Variants
+  //             ^^^^^^^^^  -> Base
+  let mut raw_variants = segment(input, b':');
+
+  if let Some(prefix) = &design.prefix {
+    let Some(new_variants) = raw_variants.strip_prefix(prefix) else {
+      return None;
+    };
+
+    if new_variants.is_empty() {
+      return None;
+    }
+
+    raw_variants = new_variants.to_vec();
+  }
+
+  // Safety: At this point it is safe to use TypeScript's non-null assertion
+  // operator because even if the `input` was an empty string, splitting an
+  // empty string by `:` will always result in an array with at least one
+  // element.
+  let mut base = raw_variants.pop().unwrap();
+
+  let mut parsed_variants: Vec<Variant> = Vec::with_capacity(raw_variants.len());
+
+  for i in (0..raw_variants.len()).rev() {
+    let parsed_variant = parse_variant(raw_variants[i]);
+    if parsed_variant.is_none() {
+      return None;
+    }
+
+    parsed_variants.push(parsed_variant.unwrap())
+  }
+
+  let mut important = false;
+  let mut negative = false;
+
+  // Candidates that end with an exclamation mark are the important version with
+  // higher specificity of the non-important candidate, e.g. `mx-4!`.
+  if let Some(new_base) = base.strip_suffix(b"!") {
+    important = true;
+    base = new_base;
+  }
+
+  // Legacy syntax with leading `!`, e.g. `!mx-4`.
+  else if let Some(new_base) = base.strip_prefix(b"!") {
+    important = true;
+    base = new_base;
+  }
+
+  // Candidates that start with a dash are the negative versions of another
+  // candidate, e.g. `-mx-4`.
+  if let Some(new_base) = base.strip_prefix(b"-") {
+    negative = true;
+    base = new_base;
+  }
+
+  let mut utilities: Vec<Utility> = vec![];
+
+  // Check for an exact match of a static utility first as long as it does not
+  // look like an arbitrary value.
+  if design.utilities.has(base) && !base.contains(&b'[') {
+    utilities.push(Utility::Static {
+      root: base.to_vec(),
+    });
+  }
+
+  // Figure out the new base and the modifier segment if present.
+  //
+  // E.g.:
+  //
+  // ```
+  // bg-red-500/50
+  // ^^^^^^^^^^    -> Base without modifier
+  //            ^^ -> Modifier segment
+  // ```
+  let parts = segment(base, b'/');
+
+  // If there's more than one modifier, the utility is invalid.
+  //
+  // E.g.:
+  //
+  // - `bg-red-500/50/50`
+  if parts.len() > 2 {
+    return None;
+  }
+
+  // let [baseWithoutModifier, modifierSegment = null, additionalModifier] = segment(base, '/')
+
+
+  Some(Candidate {
+    raw: raw.to_vec(),
+    important,
+    variants: parsed_variants.to_vec(),
+    utilities,
+  })
+}
+
+fn parse_variant(input: &[u8]) -> Option<Variant> {
+  return Some(Variant::Static { root: vec![], compounds: false })
+}
+
+fn parse_arbitrary_property(base: &[u8]) -> Option<Utility> {
+  // Arbitrary properties must start and end with square brackets.
+  let Some(base) = base.strip_prefix(b"[") else {
+    return None;
+  };
+
+  let Some(base) = base.strip_suffix(b"]") else {
+    return None;
+  };
+
+  // The property part of the arbitrary property can only start with a-z
+  // lowercase or a dash `-` in case of vendor prefixes such as `-webkit-`
+  // or `-moz-`.
+  //
+  // Otherwise, it is an invalid candidate, and skip continue parsing.
+  if base[0] != b'-' && !(base[0] >= b'a' && base[0] <= b'z') {
+    return None
+  }
+
+  // Arbitrary properties consist of a property and a value separated by a
+  // `:`. If the `:` cannot be found, then it is an invalid candidate, and we
+  // can skip continue parsing.
+  //
+  // Since the property and the value should be separated by a `:`, we can
+  // also verify that the colon is not the first or last character in the
+  // candidate, because that would make it invalid as well.
+  let Some(idx) = base.find(b":") else {
+    return None;
+  };
+
+  if idx == 0 || idx == base.len() - 1 {
+    return None;
+  }
+
+  let property = base[..idx].to_vec();
+  let value = base[idx+1..].to_vec();
+
+  // let value = decodeArbitraryValue(base.slice(idx + 1))
+
+  Some(Utility::Arbitrary {
+    property,
+    value,
+    modifier: None,
+  })
+}

crates/core/src/engine/mod.rs

@@ -0,0 +1,10 @@
+// mod candidate;
+
+/// This represents the core logic of:
+/// - Parsing a candidate
+/// - Matching that against a list of known utilities and known variants
+/// - Returning the appropriate "functions" to be called
+
+struct Engine {
+  //
+}

crates/core/src/lib.rs

@@ -0,0 +1,139 @@
+mod compat;
+mod css;
+mod util;
+mod compiler;
+mod engine;
+
+use css::optimize::optimize_ast;
+use css::parser::parse;
+use wasm_bindgen::prelude::*;
+use std::cell::Cell;
+use css::ast::CssNode;
+use css::visit::WalkAction;
+
+#[wasm_bindgen]
+pub fn wip() {
+  // 1. Parse the CSS
+  let mut ast = parse(b"h1 { color: red; font-size: 2em; } h2 { color: blue; font-size: 1.5em; }").unwrap();
+
+  // 2. Walk the AST and mutate all color properties to green
+  ast.walk_mut(&mut |node| {
+    let CssNode::Declaration { property, value, .. } = node else {
+      return WalkAction::Continue;
+    };
+
+    if property != b"color" {
+      return WalkAction::Continue;
+    }
+
+    *value = "green".into();
+
+    return WalkAction::Continue;
+  });
+
+  // 3. Walk the AST and count the number of font-size properties
+  let count = Cell::new(0);
+
+  ast.walk(&|node| {
+    let CssNode::Declaration { property, .. } = node else {
+      return WalkAction::Continue;
+    };
+
+    if property != b"font-size" {
+      return WalkAction::Continue;
+    }
+
+    count.set(count.get() + 1);
+
+    WalkAction::Continue
+  });
+
+  // 4. Optimize the AST
+  optimize_ast(&mut ast);
+
+  // 5. Serialize the AST back to CSS
+  let css = ast.to_css();
+
+  // 6. Print the CSS
+  println!("{}", String::from_utf8_lossy(&css));
+  println!("{}", count.get());
+}
+
+// use css::ast::{decl, rule, Ast, AstNode, WalkAction};
+
+// pub struct Compiler {
+//   ast: Stylesheet,
+//   config_paths: Vec<String>,
+//   plugin_paths: Vec<String>,
+// }
+
+// impl Compiler {
+//   fn new(css: &[u8]) -> Compiler {
+//     let mut ast = parse_css(css);
+//     let mut plugin_paths = vec![];
+//     let mut config_paths = vec![];
+
+//     ast.walk(&mut |node, _| {
+//       let AstNode::Rule { selector, .. } = node else {
+//         return WalkAction::Continue;
+//       };
+
+//       if selector.starts_with(b"@plugin") {
+//         let path = selector.split_at(7).1;
+//         let path = &path[2..path.len()-1];
+//         let path = path.to_vec();
+
+//         plugin_paths.push(unsafe {
+//           String::from_utf8_unchecked(path)
+//         });
+//       }
+
+//       if selector.starts_with(b"@config") {
+//         let path = selector.split_at(7).1;
+//         let path = &path[2..path.len()-1];
+//         let path = path.to_vec();
+
+//         config_paths.push(unsafe {
+//           String::from_utf8_unchecked(path)
+//         });
+//       }
+
+//       WalkAction::Continue
+//     });
+
+//     Compiler {
+//       ast,
+//     }
+//   }
+
+//   // fn plugin_paths(&self) -> Vec<String> {
+//   //   vec![]
+//   // }
+
+//   // fn config_paths(&self) -> Vec<String> {
+//   //   vec![]
+//   // }
+// }
+
+// fn parse_css(css: &[u8]) -> Ast {
+//   // TODO: Parse the CSS into an AST
+//   _ = css;
+
+//   Ast::from(vec![
+//     rule(b"body", vec![
+//       decl(b"color", Some(b"red"), false),
+//     ]),
+//   ])
+// }
+
+// fn foo() {
+//   let css = b"body { color: red; }";
+//   let compiler = Compiler::new(css);
+// }
+
+// enum UtilityDescriptor {
+//   Simple {
+//     name: String,
+//     ast: Ast,
+//   },
+// }

crates/core/src/main.rs

@@ -0,0 +1,380 @@
+use std::hint::black_box;
+
+const PREFLIGHT: &'static str = r#"/*
+  1. Prevent padding and border from affecting element width. (https://github.com/mozdevs/cssremedy/issues/4)
+  2. Remove default margins and padding
+  3. Reset all borders.
+*/
+
+*,
+::after,
+::before,
+::backdrop,
+::file-selector-button {
+  box-sizing: border-box; /* 1 */
+  margin: 0; /* 2 */
+  padding: 0; /* 2 */
+  border: 0 solid; /* 3 */
+}
+
+/*
+  1. Use a consistent sensible line-height in all browsers.
+  2. Prevent adjustments of font size after orientation changes in iOS.
+  3. Use a more readable tab size.
+  4. Use the user's configured `sans` font-family by default.
+  5. Use the user's configured `sans` font-feature-settings by default.
+  6. Use the user's configured `sans` font-variation-settings by default.
+  7. Disable tap highlights on iOS.
+*/
+
+html,
+:host {
+  line-height: 1.5; /* 1 */
+  -webkit-text-size-adjust: 100%; /* 2 */
+  tab-size: 4; /* 3 */
+  font-family: var(
+    --default-font-family,
+    ui-sans-serif,
+    system-ui,
+    sans-serif,
+    'Apple Color Emoji',
+    'Segoe UI Emoji',
+    'Segoe UI Symbol',
+    'Noto Color Emoji'
+  ); /* 4 */
+  font-feature-settings: var(--default-font-feature-settings, normal); /* 5 */
+  font-variation-settings: var(--default-font-variation-settings, normal); /* 6 */
+  -webkit-tap-highlight-color: transparent; /* 7 */
+}
+
+/*
+  Inherit line-height from `html` so users can set them as a class directly on the `html` element.
+*/
+
+body {
+  line-height: inherit;
+}
+
+/*
+  1. Add the correct height in Firefox.
+  2. Correct the inheritance of border color in Firefox. (https://bugzilla.mozilla.org/show_bug.cgi?id=190655)
+  3. Reset the default border style to a 1px solid border.
+*/
+
+hr {
+  height: 0; /* 1 */
+  color: inherit; /* 2 */
+  border-top-width: 1px; /* 3 */
+}
+
+/*
+  Add the correct text decoration in Chrome, Edge, and Safari.
+*/
+
+abbr:where([title]) {
+  -webkit-text-decoration: underline dotted;
+  text-decoration: underline dotted;
+}
+
+/*
+  Remove the default font size and weight for headings.
+*/
+
+h1,
+h2,
+h3,
+h4,
+h5,
+h6 {
+  font-size: inherit;
+  font-weight: inherit;
+}
+
+/*
+  Reset links to optimize for opt-in styling instead of opt-out.
+*/
+
+a {
+  color: inherit;
+  -webkit-text-decoration: inherit;
+  text-decoration: inherit;
+}
+
+/*
+  Add the correct font weight in Edge and Safari.
+*/
+
+b,
+strong {
+  font-weight: bolder;
+}
+
+/*
+  1. Use the user's configured `mono` font-family by default.
+  2. Use the user's configured `mono` font-feature-settings by default.
+  3. Use the user's configured `mono` font-variation-settings by default.
+  4. Correct the odd `em` font sizing in all browsers.
+*/
+
+code,
+kbd,
+samp,
+pre {
+  font-family: var(
+    --default-mono-font-family,
+    ui-monospace,
+    SFMono-Regular,
+    Menlo,
+    Monaco,
+    Consolas,
+    'Liberation Mono',
+    'Courier New',
+    monospace
+  ); /* 4 */
+  font-feature-settings: var(--default-mono-font-feature-settings, normal); /* 5 */
+  font-variation-settings: var(--default-mono-font-variation-settings, normal); /* 6 */
+  font-size: 1em; /* 4 */
+}
+
+/*
+  Add the correct font size in all browsers.
+*/
+
+small {
+  font-size: 80%;
+}
+
+/*
+  Prevent `sub` and `sup` elements from affecting the line height in all browsers.
+*/
+
+sub,
+sup {
+  font-size: 75%;
+  line-height: 0;
+  position: relative;
+  vertical-align: baseline;
+}
+
+sub {
+  bottom: -0.25em;
+}
+
+sup {
+  top: -0.5em;
+}
+
+/*
+  1. Remove text indentation from table contents in Chrome and Safari. (https://bugs.chromium.org/p/chromium/issues/detail?id=999088, https://bugs.webkit.org/show_bug.cgi?id=201297)
+  2. Correct table border color inheritance in all Chrome and Safari. (https://bugs.chromium.org/p/chromium/issues/detail?id=935729, https://bugs.webkit.org/show_bug.cgi?id=195016)
+  3. Remove gaps between table borders by default.
+*/
+
+table {
+  text-indent: 0; /* 1 */
+  border-color: inherit; /* 2 */
+  border-collapse: collapse; /* 3 */
+}
+
+/*
+  1. Inherit the font styles in all browsers.
+  2. Remove the default background color.
+*/
+
+button,
+input,
+optgroup,
+select,
+textarea,
+::file-selector-button {
+  font: inherit; /* 1 */
+  font-feature-settings: inherit; /* 1 */
+  font-variation-settings: inherit; /* 1 */
+  letter-spacing: inherit; /* 1 */
+  color: inherit; /* 1 */
+  background: transparent; /* 2 */
+}
+
+/*
+  Reset the default inset border style for form controls to solid.
+*/
+
+input:where(:not([type='button'], [type='reset'], [type='submit'])),
+select,
+textarea {
+  border: 1px solid;
+}
+
+/*
+  Correct the inability to style the border radius in iOS Safari.
+*/
+button,
+input:where([type='button'], [type='reset'], [type='submit']),
+::file-selector-button {
+  appearance: button;
+}
+
+/*
+  Use the modern Firefox focus style for all focusable elements.
+*/
+
+:-moz-focusring {
+  outline: auto;
+}
+
+/*
+  Remove the additional `:invalid` styles in Firefox. (https://github.com/mozilla/gecko-dev/blob/2f9eacd9d3d995c937b4251a5557d95d494c9be1/layout/style/res/forms.css#L728-L737)
+*/
+
+:-moz-ui-invalid {
+  box-shadow: none;
+}
+
+/*
+  Add the correct vertical alignment in Chrome and Firefox.
+*/
+
+progress {
+  vertical-align: baseline;
+}
+
+/*
+  Correct the cursor style of increment and decrement buttons in Safari.
+*/
+
+::-webkit-inner-spin-button,
+::-webkit-outer-spin-button {
+  height: auto;
+}
+
+/*
+  Remove the inner padding in Chrome and Safari on macOS.
+*/
+
+::-webkit-search-decoration {
+  -webkit-appearance: none;
+}
+
+/*
+  Add the correct display in Chrome and Safari.
+*/
+
+summary {
+  display: list-item;
+}
+
+/*
+  Make lists unstyled by default.
+*/
+
+ol,
+ul,
+menu {
+  list-style: none;
+}
+
+/*
+  Prevent resizing textareas horizontally by default.
+*/
+
+textarea {
+  resize: vertical;
+}
+
+/*
+  1. Reset the default placeholder opacity in Firefox. (https://github.com/tailwindlabs/tailwindcss/issues/3300)
+  2. Set the default placeholder color to a semi-transparent version of the current text color.
+*/
+
+::placeholder {
+  opacity: 1; /* 1 */
+  color: color-mix(in srgb, currentColor 50%, transparent); /* 2 */
+}
+
+/*
+  1. Make replaced elements `display: block` by default. (https://github.com/mozdevs/cssremedy/issues/14)
+  2. Add `vertical-align: middle` to align replaced elements more sensibly by default. (https://github.com/jensimmons/cssremedy/issues/14#issuecomment-634934210)
+      This can trigger a poorly considered lint error in some tools but is included by design.
+*/
+
+img,
+svg,
+video,
+canvas,
+audio,
+iframe,
+embed,
+object {
+  display: block; /* 1 */
+  vertical-align: middle; /* 2 */
+}
+
+/*
+  Constrain images and videos to the parent width and preserve their intrinsic aspect ratio. (https://github.com/mozdevs/cssremedy/issues/14)
+*/
+
+img,
+video {
+  max-width: 100%;
+  height: auto;
+}
+
+/*
+  Make elements with the HTML hidden attribute stay hidden by default.
+*/
+
+[hidden] {
+  display: none !important;
+}
+"#;
+
+mod css;
+mod util;
+
+pub fn main() {
+  let throughput = util::Throughput::compute(100_000, PREFLIGHT.len(), || {
+    _ = black_box(css::parse(PREFLIGHT.as_bytes()));
+  });
+
+  eprintln!("css::parse: {:}", throughput);
+
+  let input = &b"var(--a, 0 0 1px rgb(0, 0, 0)), 0 0 1px rgb(0, 0, 0), var(--a, 0 0 1px rgb(0, 0, 0)), 0 0 1px rgb(0, 0, 0), ".repeat(500)[..];
+
+  let throughput = util::Throughput::compute(100_000, input.len(), || {
+    _ = black_box(util::segment(input, b','));
+  });
+
+  eprintln!("util::segment: {:}", throughput);
+
+  let input = &b"s\\o\\m\\e\\_\\identifier_token ".repeat(500)[..];
+
+  let throughput = util::Throughput::compute(100_000_000, input.len(), || {
+    _ = black_box(css::syntax::read_ident_token(input));
+  });
+
+  eprintln!("css::syntax::read_ident_token: {:}", throughput);
+
+  let input = &b"@media           (min-width: 1280px)    ".repeat(500)[..];
+
+  let throughput = util::Throughput::compute(2_000_000, input.len(), || {
+    _ = black_box(css::parser::parse_rule_header(input));
+  });
+
+  eprintln!("css::parser::parse_rule_header (at rule): {:}", throughput);
+
+  let input = &b".foo.bar:is(.baz:has(.qux:where(.foo + .bar))) + .thing::before".repeat(500)[..];
+
+  let throughput = util::Throughput::compute(2_000_000, input.len(), || {
+    _ = black_box(css::parser::parse_rule_header(input));
+  });
+
+  eprintln!("css::parser::parse_rule_header (style rule): {:}", throughput);
+
+  let input = &b"[content-start]_calc(100%-1px)_[content-end]_minmax(1rem,1fr)".repeat(500)[..];
+
+  let throughput = util::Throughput::compute(100_000, input.len(), || {
+    _ = black_box(util::convert_underscores_to_whitespace(input));
+  });
+
+  eprintln!("util::convert_underscores_to_whitespace: {:}", throughput);
+}

crates/core/src/util/decode.rs

@@ -0,0 +1,122 @@
+// import { addWhitespaceAroundMathOperators } from './math-operators'
+
+use std::mem;
+
+pub fn decode_arbitrary_value(input: &[u8]) -> Vec<u8> {
+  // We do not want to normalize anything inside of a url() because if we
+  // replace `_` with ` `, then it will very likely break the url.
+  if input.starts_with(b"url(") {
+    return input.to_vec()
+  }
+
+  let input = convert_underscores_to_whitespace(input);
+  // let input = addWhitespaceAroundMathOperators(input);
+
+  return input.to_vec();
+}
+
+/// Convert `_` to ` ` unless escaped (`\_`) in which case they
+/// should be converted to `_` instead.
+pub fn convert_underscores_to_whitespace(input: &[u8]) -> Vec<u8> {
+  let mut result = Vec::<u8>::with_capacity(input.len());
+
+  let input = write_decoded_8(input, &mut result);
+  write_decoded_scalar(input, &mut result);
+
+  result
+}
+
+pub fn write_decoded_8<'a, 'b>(input: &'a [u8], result: &'b mut Vec<u8>) -> &'a [u8] {
+  const CHUNK_SIZE: usize = mem::size_of::<u64>();
+  const NUL_8: [u8; CHUNK_SIZE] = [0x00; CHUNK_SIZE];
+  const SPACE_8: [u8; CHUNK_SIZE] = [b' '; CHUNK_SIZE];
+  const ESCAPE_8: [u8; CHUNK_SIZE] = [b'\\'; CHUNK_SIZE];
+  const UNDERSCORE_8: [u8; CHUNK_SIZE] = [b'_'; CHUNK_SIZE];
+
+  let mut chunks = input.chunks_exact(CHUNK_SIZE);
+
+  while let Some(chunk) = chunks.next() {
+    let mut chunk: [u8; CHUNK_SIZE] = chunk.try_into().unwrap();
+    let mut chunk: u64 = u64::from_ne_bytes(chunk);
+
+    let mut is_escape = [false; CHUNK_SIZE];
+    for j in 0..CHUNK_SIZE {
+      is_escape[j] = chunk[j] == b'\\';
+    }
+
+    let mut is_underscore = [false; CHUNK_SIZE];
+    for j in 0..CHUNK_SIZE {
+      is_underscore[j] = chunk[j] == b'_';
+    }
+
+    // Replace underscores with spaces in the chunk
+    for j in 0..CHUNK_SIZE {
+      chunk[j] = if is_underscore[j] {
+        SPACE_8[j]
+      } else {
+        chunk[j]
+      };
+    }
+
+    // Replace escaped underscores with underscores
+    for j in 0..(CHUNK_SIZE - 1) {
+      chunk[j] = if is_escape[j] && is_underscore[j + 1] {
+        UNDERSCORE_8[j]
+      } else {
+        chunk[j]
+      };
+    }
+
+    // Replace escapes with NUL bytes
+    for j in 0..CHUNK_SIZE {
+      chunk[j] = if is_escape[j] {
+        NUL_8[j]
+      } else {
+        chunk[j]
+      };
+    }
+
+    result.extend(&chunk);
+  }
+
+  return chunks.remainder();
+}
+
+
+pub fn write_decoded_scalar(input: &[u8], result: &mut Vec<u8>) {
+  let mut i = 0;
+
+  while i < input.len() {
+    match input[i] {
+      b'\\' => {
+        if i + 1 == input.len() {
+          // We've hit the end of the string and there's no character to escape
+          result.extend(b"\\");
+        } else if input[i + 1] == b'_' {
+          // We've hit an escaped underscore
+          result.extend(b"_");
+        } else {
+          // We've hit an "escaped" character that isn't an underscore
+          // which means its not actually escaped and should be treated
+          // as a literal character. Since we've already read the next
+          // character, we'll just write both of them out here.
+          result.extend(&input[i..i+1]);
+        }
+
+        i += 2;
+      },
+
+      b'_' => {
+        result.push(b' ');
+        i += 1;
+      },
+
+      _ => {
+        result.push(input[i]);
+        i += 1;
+      }
+    }
+  }
+}
+
+// a\b\c

crates/core/src/util/escape.rs

@@ -0,0 +1,216 @@
+#[derive(Clone, Copy)]
+enum Case {
+  Other,
+  Ident,
+  Nul,
+  Control,
+}
+
+// This list allows us to quickly identify what kind of byte we are looking at
+// and jump to the right block of code to handle it producing a roughly 2x
+// speedup in the general case.
+static __CASES: [Case; 256] = {
+  let mut cases = [Case::Other; 256];
+
+  cases[0x00] = Case::Nul;
+
+  let mut i = 0x01;
+  while i <= 0x1f {
+    cases[i] = Case::Control;
+    i+=1;
+  }
+
+  cases[0x7f] = Case::Control;
+
+  let mut i = b'0';
+  while i <= b'9' {
+    cases[i as usize] = Case::Ident;
+    i+=1;
+  }
+
+  let mut i = b'A';
+  while i <= b'Z' {
+    cases[i as usize] = Case::Ident;
+    i+=1;
+  }
+
+  let mut i = b'a';
+  while i <= b'z' {
+    cases[i as usize] = Case::Ident;
+    i+=1;
+  }
+
+  cases[b'-' as usize] = Case::Ident;
+  cases[b'_' as usize] = Case::Ident;
+
+  let mut i = 0x80;
+  while i <= 0xff {
+    cases[i] = Case::Ident;
+    i+=1;
+  }
+
+  cases
+};
+
+// https://drafts.csswg.org/cssom/#serialize-an-identifier
+pub fn escape(value: &[u8]) -> Vec<u8> {
+  if value.len() == 0 {
+    return vec![];
+  }
+
+  if value == b"-" {
+    return b"\\-".to_vec();
+  }
+
+  // While the worst-case is 4x the size of the input, the "average" worst case
+  // is actually 2x the size of the input. This would happen for a string
+  // consisting of all printable, non-ident characters. If we pre-allocate
+  // for this case we can avoid all re-allocations during the loop unless we
+  // happen to have enough control characters to trigger the worst-case.
+  let mut result: Vec<u8> = Vec::with_capacity(2 * value.len());
+
+  let mut value = value;
+
+  if value[0] == b'-' {
+    result.push(b'-');
+    value = &value[1..];
+  }
+
+  // SAFETY: We're guaranteed to have at least one byte in `value` at this point
+  // because if len() > 0 AND the only byte is `-` then we've already handled
+  // that case.
+  if let digit @ b'0'..=b'9' = *unsafe { value.get_unchecked(0) } {
+    write_hex_digit(digit, &mut result);
+    value = &value[1..];
+  }
+
+  write_escape_scalar(value, &mut result);
+
+  return result;
+}
+
+#[inline(always)]
+fn write_escape_scalar(value: &[u8], result: &mut Vec<u8>) {
+  let replacement = "\u{FFFD}".as_bytes();
+
+  // Note: there’s no need to special-case astral symbols, surrogate
+  // pairs, or lone surrogates.
+  for &code_unit in value.iter() {
+    match __CASES[code_unit as usize] {
+      // Every character in /[0-9a-zA-Z-_]/ can be included directly
+      Case::Ident  => result.push(code_unit),
+
+      // Other printable ASCII characters should be printed with an escape
+      // https://drafts.csswg.org/cssom/#escape-a-character
+      Case::Other => result.extend([
+        b'\\',
+        code_unit,
+      ]),
+
+      // The NUL character (U+0000) becomes the REPLACEMENT CHARACTER (U+FFFD)
+      Case::Nul => result.extend(replacement),
+
+      // Control characters (U+0001–U+001F and U+007F) are written in hex
+      // https://drafts.csswg.org/cssom/#escape-a-character-as-code-point
+      Case::Control => write_hex_digit(code_unit, result),
+    }
+  }
+}
+
+pub fn write_hex_digit(value: u8, s: &mut Vec<u8>) {
+    static HEX: &[u8; 16] = b"0123456789abcdef";
+
+    if value > 0x0F {
+        let hi = value >> 4 & 0x0F;
+        let lo = value >> 0 & 0x0F;
+        s.extend([
+          b'\\',
+          HEX[hi as usize],
+          HEX[lo as usize],
+          b' ',
+        ]);
+    } else {
+      s.extend([
+        b'\\',
+        HEX[value as usize],
+        b' ',
+      ]);
+    };
+}
+
+#[cfg(test)]
+mod test {
+  use super::*;
+
+  #[test]
+  fn test() {
+    assert_eq!(escape(b"\0"), "\u{FFFD}".as_bytes());
+    assert_eq!(escape(b"a\0"), "a\u{FFFD}".as_bytes());
+    assert_eq!(escape(b"\0b"), "\u{FFFD}b".as_bytes());
+    assert_eq!(escape(b"a\0b"), "a\u{FFFD}b".as_bytes());
+
+    assert_eq!(escape("\u{FFFD}".as_bytes()), "\u{FFFD}".as_bytes());
+    assert_eq!(escape("a\u{FFFD}".as_bytes()), "a\u{FFFD}".as_bytes());
+    assert_eq!(escape("\u{FFFD}b".as_bytes()), "\u{FFFD}b".as_bytes());
+    assert_eq!(escape("a\u{FFFD}b".as_bytes()), "a\u{FFFD}b".as_bytes());
+
+    assert_eq!(escape(b""), b"");
+
+    assert_eq!(escape(b"\x01\x02\x1E\x1F"), b"\\1 \\2 \\1e \\1f ");
+
+    assert_eq!(escape(b"0a"), b"\\30 a");
+    assert_eq!(escape(b"1a"), b"\\31 a");
+    assert_eq!(escape(b"2a"), b"\\32 a");
+    assert_eq!(escape(b"3a"), b"\\33 a");
+    assert_eq!(escape(b"4a"), b"\\34 a");
+    assert_eq!(escape(b"5a"), b"\\35 a");
+    assert_eq!(escape(b"6a"), b"\\36 a");
+    assert_eq!(escape(b"7a"), b"\\37 a");
+    assert_eq!(escape(b"8a"), b"\\38 a");
+    assert_eq!(escape(b"9a"), b"\\39 a");
+
+    assert_eq!(escape(b"a0b"), b"a0b");
+    assert_eq!(escape(b"a1b"), b"a1b");
+    assert_eq!(escape(b"a2b"), b"a2b");
+    assert_eq!(escape(b"a3b"), b"a3b");
+    assert_eq!(escape(b"a4b"), b"a4b");
+    assert_eq!(escape(b"a5b"), b"a5b");
+    assert_eq!(escape(b"a6b"), b"a6b");
+    assert_eq!(escape(b"a7b"), b"a7b");
+    assert_eq!(escape(b"a8b"), b"a8b");
+    assert_eq!(escape(b"a9b"), b"a9b");
+
+    assert_eq!(escape(b"-0a"), b"-\\30 a");
+    assert_eq!(escape(b"-1a"), b"-\\31 a");
+    assert_eq!(escape(b"-2a"), b"-\\32 a");
+    assert_eq!(escape(b"-3a"), b"-\\33 a");
+    assert_eq!(escape(b"-4a"), b"-\\34 a");
+    assert_eq!(escape(b"-5a"), b"-\\35 a");
+    assert_eq!(escape(b"-6a"), b"-\\36 a");
+    assert_eq!(escape(b"-7a"), b"-\\37 a");
+    assert_eq!(escape(b"-8a"), b"-\\38 a");
+    assert_eq!(escape(b"-9a"), b"-\\39 a");
+
+    assert_eq!(escape(b"-"), b"\\-");
+    assert_eq!(escape(b"-a"), b"-a");
+    assert_eq!(escape(b"--"), b"--");
+    assert_eq!(escape(b"--a"), b"--a");
+
+    assert_eq!(escape(b"\x80\x2D\x5F\xA9"), b"\x80\x2D\x5F\xA9");
+    assert_eq!(escape(b"\x7F\x80\x81\x82\x83\x84\x85\x86\x87\x88\x89\x8A\x8B\x8C\x8D\x8E\x8F\x90\x91\x92\x93\x94\x95\x96\x97\x98\x99\x9A\x9B\x9C\x9D\x9E\x9F"), b"\\7f \x80\x81\x82\x83\x84\x85\x86\x87\x88\x89\x8A\x8B\x8C\x8D\x8E\x8F\x90\x91\x92\x93\x94\x95\x96\x97\x98\x99\x9A\x9B\x9C\x9D\x9E\x9F");
+    assert_eq!(escape(b"\xA0\xA1\xA2"), b"\xA0\xA1\xA2");
+    assert_eq!(escape(b"a0123456789b"), b"a0123456789b");
+    assert_eq!(escape(b"abcdefghijklmnopqrstuvwxyz"), b"abcdefghijklmnopqrstuvwxyz");
+    assert_eq!(escape(b"ABCDEFGHIJKLMNOPQRSTUVWXYZ"), b"ABCDEFGHIJKLMNOPQRSTUVWXYZ");
+
+    assert_eq!(escape(b"\x20\x21\x78\x79"), b"\\ \\!xy");
+
+    // astral symbol (U+1D306 TETRAGRAM FOR CENTRE)
+    assert_eq!(escape("\u{1D306}".as_bytes()), "\u{1D306}".as_bytes());
+
+    // surrogates
+    // assert_eq!(escape("\u{D834}\u{DF06}".as_bytes()), "\u{D834}\u{DF06}".as_bytes());
+    // assert_eq!(escape("\u{DF06}".as_bytes()), "\u{DF06}".as_bytes());
+    // assert_eq!(escape("\u{D834}".as_bytes()), "\u{D834}".as_bytes());
+  }
+}

crates/core/src/util/fast_stack.rs

@@ -0,0 +1,60 @@
+use super::gurantee;
+
+pub struct FastStack {
+  storage: [u8; 256],
+  pos: usize
+}
+
+impl FastStack {
+  #[inline(always)]
+  pub fn new() -> FastStack {
+    FastStack {
+      storage: [0; 256],
+      pos: 0
+    }
+  }
+
+  #[inline(always)]
+  pub fn push(&mut self, value: u8) {
+    gurantee(!self.overgrown());
+
+    self.storage[self.pos] = value;
+    self.pos += 1;
+  }
+
+  #[inline(always)]
+  pub fn peek(&self) -> u8 {
+    gurantee(!self.overgrown());
+
+    return self.storage[self.pos - 1];
+  }
+
+  #[inline(always)]
+  pub fn last(&self) -> Option<u8> {
+    if self.is_empty() || self.overgrown() {
+      return None;
+    }
+
+    return Some(self.peek());
+  }
+
+  #[inline(always)]
+  pub fn pop(&mut self) {
+    // SAFETY: The buffer does not need to be mutated because the stack is
+    // only ever read from or written to its current position. Its current
+    // position is only ever incremented after writing to it. Meaning that
+    // the buffer can be dirty for the next use and still be correct since
+    // reading/writing always starts at position `0`.
+    self.pos = self.pos.saturating_sub(1);
+  }
+
+  #[inline(always)]
+  pub fn is_empty(&self) -> bool {
+    return self.pos == 0;
+  }
+
+  #[inline(always)]
+  pub fn overgrown(&self) -> bool {
+    self.pos > 256
+  }
+}

crates/core/src/util/gurantee.rs

@@ -0,0 +1,11 @@
+#[inline(always)]
+pub const fn gurantee(expr: bool) {
+  #[cfg(debug_assertions)]
+  if !expr {
+    panic!("gurantee failed")
+  }
+
+  unsafe {
+    std::hint::assert_unchecked(expr)
+  }
+}

crates/core/src/util/math.rs

@@ -0,0 +1,154 @@
+// const mathFunctions = [
+//   'calc',
+//   'min',
+//   'max',
+//   'clamp',
+//   'mod',
+//   'rem',
+//   'sin',
+//   'cos',
+//   'tan',
+//   'asin',
+//   'acos',
+//   'atan',
+//   'atan2',
+//   'pow',
+//   'sqrt',
+//   'hypot',
+//   'log',
+//   'exp',
+//   'round',
+// ]
+
+// export function hasMathFn(input: string) {
+//   return input.indexOf('(') !== -1 && mathFunctions.some((fn) => input.includes(`${fn}(`))
+// }
+
+// export function addWhitespaceAroundMathOperators(input: string) {
+//   // There's definitely no functions in the input, so bail early
+//   if (input.indexOf('(') === -1) {
+//     return input
+//   }
+
+//   // Bail early if there are no math functions in the input
+//   if (!mathFunctions.some((fn) => input.includes(fn))) {
+//     return input
+//   }
+
+//   let result = ''
+//   let formattable: boolean[] = []
+
+//   for (let i = 0; i < input.length; i++) {
+//     let char = input[i]
+
+//     // Determine if we're inside a math function
+//     if (char === '(') {
+//       result += char
+
+//       // Scan backwards to determine the function name. This assumes math
+//       // functions are named with lowercase alphanumeric characters.
+//       let start = i
+
+//       for (let j = i - 1; j >= 0; j--) {
+//         let inner = input.charCodeAt(j)
+
+//         if (inner >= 48 && inner <= 57) {
+//           start = j // 0-9
+//         } else if (inner >= 97 && inner <= 122) {
+//           start = j // a-z
+//         } else {
+//           break
+//         }
+//       }
+
+//       let fn = input.slice(start, i)
+
+//       // This is a known math function so start formatting
+//       if (mathFunctions.includes(fn)) {
+//         formattable.unshift(true)
+//         continue
+//       }
+
+//       // We've encountered nested parens inside a math function, record that and
+//       // keep formatting until we've closed all parens.
+//       else if (formattable[0] && fn === '') {
+//         formattable.unshift(true)
+//         continue
+//       }
+
+//       // This is not a known math function so don't format it
+//       formattable.unshift(false)
+//       continue
+//     }
+
+//     // We've exited the function so format according to the parent function's
+//     // type.
+//     else if (char === ')') {
+//       result += char
+//       formattable.shift()
+//     }
+
+//     // Add spaces after commas in math functions
+//     else if (char === ',' && formattable[0]) {
+//       result += `, `
+//       continue
+//     }
+
+//     // Skip over consecutive whitespace
+//     else if (char === ' ' && formattable[0] && result[result.length - 1] === ' ') {
+//       continue
+//     }
+
+//     // Add whitespace around operators inside math functions
+//     else if ((char === '+' || char === '*' || char === '/' || char === '-') && formattable[0]) {
+//       let trimmed = result.trimEnd()
+//       let prev = trimmed[trimmed.length - 1]
+
+//       // If we're preceded by an operator don't add spaces
+//       if (prev === '+' || prev === '*' || prev === '/' || prev === '-') {
+//         result += char
+//         continue
+//       }
+
+//       // If we're at the beginning of an argument don't add spaces
+//       else if (prev === '(' || prev === ',') {
+//         result += char
+//         continue
+//       }
+
+//       // Add spaces only after the operator if we already have spaces before it
+//       else if (input[i - 1] === ' ') {
+//         result += `${char} `
+//       }
+
+//       // Add spaces around the operator
+//       else {
+//         result += ` ${char} `
+//       }
+//     }
+
+//     // Skip over `to-zero` when in a math function.
+//     //
+//     // This is specifically to handle this value in the round(…) function:
+//     //
+//     // ```
+//     // round(to-zero, 1px)
+//     //       ^^^^^^^
+//     // ```
+//     //
+//     // This is because the first argument is optionally a keyword and `to-zero`
+//     // contains a hyphen and we want to avoid adding spaces inside it.
+//     else if (formattable[0] && input.startsWith('to-zero', i)) {
+//       let start = i
+//       i += 7
+//       result += input.slice(start, i + 1)
+//     }
+
+//     // Handle all other characters
+//     else {
+//       result += char
+//     }
+//   }
+
+//   return result
+// }

crates/core/src/util/mod.rs

@@ -0,0 +1,28 @@
+mod decode;
+mod escape;
+mod fast_stack;
+mod gurantee;
+mod math;
+mod segment;
+mod throughput;
+
+#[allow(unused_imports)]
+pub use crate::util::decode::*;
+
+#[allow(unused_imports)]
+pub use crate::util::math::*;
+
+#[allow(unused_imports)]
+pub use crate::util::escape::*;
+
+#[allow(unused_imports)]
+pub use crate::util::fast_stack::*;
+
+#[allow(unused_imports)]
+pub use crate::util::gurantee::*;
+
+#[allow(unused_imports)]
+pub use crate::util::segment::*;
+
+#[allow(unused_imports)]
+pub use crate::util::throughput::*;

crates/core/src/util/segment.rs

@@ -0,0 +1,241 @@
+use crate::util::gurantee::gurantee;
+
+use super::fast_stack::FastStack;
+
+// The order of these cases is important for performance
+// please do not change it without significant profiling
+#[derive(Copy, Clone)]
+enum Case {
+  Other,
+
+  // This makes things faster
+  // It has to be the 2nd case
+  Dummy1,
+
+  Close, // b')'
+  ParenL, // b'('
+  BracketL, // b'['
+  CurlyL, // b'{'
+
+  Escape, // b'\'
+  QuoteDouble, // b'"'
+  QuoteSingle, // b'\''
+  Separator, // other
+}
+
+const fn generate_cases(separator: u8) -> [Case; 256] {
+  let mut table = [Case::Other; 256];
+
+  table[b'\\' as usize] = Case::Escape;
+  table[b'"' as usize] = Case::QuoteDouble;
+  table[b'\'' as usize] = Case::QuoteSingle;
+  table[b'(' as usize] = Case::ParenL;
+  table[b'[' as usize] = Case::BracketL;
+  table[b'{' as usize] = Case::CurlyL;
+  table[b')' as usize] = Case::Close;
+  table[b']' as usize] = Case::Close;
+  table[b'}' as usize] = Case::Close;
+  table[separator as usize] = Case::Separator;
+
+  return table;
+}
+
+/**
+ * This splits a string on a top-level character.
+ *
+ * Regex doesn't support recursion (at least not the JS-flavored version),
+ * so we have to use a tiny state machine to keep track of paren placement.
+ *
+ * Expected behavior using commas:
+ * var(--a, 0 0 1px rgb(0, 0, 0)), 0 0 1px rgb(0, 0, 0)
+ *        ┬              ┬  ┬    ┬
+ *        x              x  x    ╰──────── Split because top-level
+ *        ╰──────────────┴──┴───────────── Ignored b/c inside >= 1 levels of parens
+ */
+#[inline(never)]
+#[no_mangle]
+pub fn segment(input: &[u8], separator: u8) -> Vec<&[u8]> {
+  return segment_table(input, generate_cases(separator))
+}
+
+#[inline(always)]
+fn segment_table(input: &[u8], cases: [Case; 256]) -> Vec<&[u8]> {
+  let mut closing_bracket_stack = FastStack::new();
+
+  let mut parts: Vec<&[u8]> = vec![];
+  let mut last_pos = 0;
+
+  let mut idx = 0;
+  while idx < input.len() {
+    // SAFETY: last_pos can never be greater than idx at the start of the loop
+    // body. It's set to one greater than idx on a separator but idx is always
+    // incremented before the next iteration.
+    gurantee(last_pos <= idx);
+
+    match cases[input[idx] as usize] {
+      Case::Separator => {
+        if closing_bracket_stack.is_empty() {
+          parts.push(&input[last_pos..idx]);
+          last_pos = idx + 1;
+        }
+      }
+
+      // The next character is escaped, so we skip it.
+      Case::Escape => idx += 1,
+
+      // Strings should be handled as-is until the end of the string. No need to
+      // worry about balancing parens, brackets, or curlies inside a string.
+      Case::QuoteDouble => {
+        loop {
+          idx += 1;
+
+          // Ensure we don't go out of bounds.
+          if idx >= input.len() {
+            break
+          }
+
+          match cases[input[idx] as usize] {
+            Case::Escape => idx += 1,
+            Case::QuoteDouble => break,
+            _ => {},
+          }
+        }
+      }
+
+      // Strings should be handled as-is until the end of the string. No need to
+      // worry about balancing parens, brackets, or curlies inside a string.
+      Case::QuoteSingle => {
+        loop {
+          idx += 1;
+
+          // Ensure we don't go out of bounds.
+          if idx >= input.len() {
+            break
+          }
+
+          match cases[input[idx] as usize] {
+            Case::Escape => idx += 1,
+            Case::QuoteSingle => break,
+            _ => {},
+          }
+        }
+      }
+
+      Case::ParenL => {
+        closing_bracket_stack.push(b')');
+
+        if closing_bracket_stack.overgrown() {
+          break
+        }
+      }
+
+      Case::BracketL => {
+        closing_bracket_stack.push(b']');
+
+        if closing_bracket_stack.overgrown() {
+          break
+        }
+      }
+
+      Case::CurlyL => {
+        closing_bracket_stack.push(b'}');
+
+        if closing_bracket_stack.overgrown() {
+          break
+        }
+      }
+
+      Case::Close => {
+        if !closing_bracket_stack.is_empty() && closing_bracket_stack.peek() == input[idx] {
+          closing_bracket_stack.pop();
+        }
+      }
+
+      Case::Other => {},
+      Case::Dummy1 => {},
+    }
+
+    idx += 1;
+  }
+
+  // SAFETY: last_pos will be at most `input.len() - 1` ensuring that the slice
+  // is always within bounds.
+  gurantee(last_pos < input.len());
+
+  parts.push(&input[last_pos..]);
+
+  return parts
+}
+
+#[cfg(test)]
+mod tests {
+  use super::*;
+
+  #[test]
+  fn should_result_in_a_single_segment_when_the_separator_is_not_present() {
+    assert_eq!(segment(b"foo", b':'), vec![b"foo"])
+  }
+
+  #[test]
+  fn should_split_by_the_separator() {
+    assert_eq!(segment(b"foo:bar:baz", b':'), vec![b"foo" as &[u8], b"bar", b"baz"])
+  }
+
+  #[test]
+  fn should_not_split_inside_of_parens() {
+    assert_eq!(segment(b"a:(b:c):d", b':'), vec![b"a" as &[u8], b"(b:c)", b"d"])
+  }
+
+  #[test]
+  fn should_not_split_inside_of_brackets() {
+    assert_eq!(segment(b"a:[b:c]:d", b':'), vec![b"a" as &[u8], b"[b:c]", b"d"])
+  }
+
+  #[test]
+  fn should_not_split_inside_of_curlies() {
+    assert_eq!(segment(b"a:{b:c}:d", b':'), vec![b"a" as &[u8], b"{b:c}", b"d"])
+  }
+
+  #[test]
+  fn should_not_split_inside_of_double_quotes() {
+    assert_eq!(segment(b"a:\"b:c\":d", b':'), vec![b"a" as &[u8], b"\"b:c\"", b"d"])
+  }
+
+  #[test]
+  fn should_not_split_inside_of_single_quotes() {
+    assert_eq!(segment(b"a:'b:c':d", b':'), vec![b"a" as &[u8], b"'b:c'", b"d"])
+  }
+
+  #[test]
+  fn should_not_crash_when_double_quotes_are_unbalanced() {
+    assert_eq!(segment(b"a:\"b:c:d", b':'), vec![b"a" as &[u8], b"\"b:c:d"])
+  }
+
+  #[test]
+  fn should_not_crash_when_single_quotes_are_unbalanced() {
+    assert_eq!(segment(b"a:'b:c:d", b':'), vec![b"a" as &[u8], b"'b:c:d"])
+  }
+
+  #[test]
+  fn should_skip_escaped_double_quotes() {
+    assert_eq!(segment(b"a:\"b:c\\\":d\":e", b':'), vec![b"a" as &[u8], b"\"b:c\\\":d\"", b"e"])
+  }
+
+  #[test]
+  fn should_skip_escaped_single_quotes() {
+    assert_eq!(segment(b"a:'b:c\\':d':e", b':'), vec![b"a" as &[u8], b"'b:c\\':d'", b"e"])
+  }
+
+  #[test]
+  fn should_skip_escaped_separators() {
+    assert_eq!(segment(b"a:b\\:c:d", b':'), vec![b"a" as &[u8], b"b\\:c", b"d"])
+  }
+
+  #[test]
+  fn should_split_by_the_escape_sequence_which_is_escape_as_well() {
+    assert_eq!(segment(b"a\\b\\c\\d", b'\\'), vec![b"a" as &[u8], b"b", b"c", b"d"]);
+    assert_eq!(segment(b"a\\(b\\c)\\d", b'\\'), vec![b"a" as &[u8], b"(b\\c)", b"d"]);
+    assert_eq!(segment(b"a\\[b\\c]\\d", b'\\'), vec![b"a" as &[u8], b"[b\\c]", b"d"]);
+    assert_eq!(segment(b"a\\{b\\c}\\d", b'\\'), vec![b"a" as &[u8], b"{b\\c}", b"d"]);
+  }
+}

crates/core/src/util/throughput.rs

@@ -0,0 +1,47 @@
+use std::fmt::Display;
+
+pub struct Throughput {
+  rate: f64,
+  elapsed: std::time::Duration,
+}
+
+impl Display for Throughput {
+  #[inline(always)]
+  fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+    write!(f, "{}/s over {:.2}s", format_byte_size(self.rate), self.elapsed.as_secs_f64())
+  }
+}
+
+impl Throughput {
+  #[inline(always)]
+  pub fn compute<F>(iterations: usize, memory_baseline: usize, cb: F) -> Self
+  where
+    F: Fn(),
+  {
+    let now = std::time::Instant::now();
+    for _ in 0..iterations {
+      cb();
+    }
+    let elapsed = now.elapsed();
+    let memory_size = iterations * memory_baseline;
+
+    Self {
+      rate: memory_size as f64 / elapsed.as_secs_f64(),
+      elapsed,
+    }
+  }
+}
+
+#[inline(always)]
+fn format_byte_size(size: f64) -> String {
+  let units = ["B", "KB", "MB", "GB", "TB", "PB", "EB", "ZB", "YB"];
+  let unit = 1000;
+  let mut size = size;
+  let mut i = 0;
+  while size > unit as f64 {
+    size /= unit as f64;
+    i += 1;
+  }
+
+  format!("{:.2} {}", size, units[i])
+}

crates/oxide/src/cursor.rs

@@ -2,10 +2,10 @@ use std::{ascii::escape_default, fmt::Display};
 
 #[derive(Debug, Clone)]
 pub struct Cursor<'a> {
-    // The input we're scanning
+    /// The input we're scanning
     pub input: &'a [u8],
 
-    // The location of the cursor in the input
+    /// The location of the cursor in the input
     pub pos: usize,
 
     /// Is the cursor at the start of the input

crates/oxide/src/extractor.rs

@@ -0,0 +1,116 @@
+/// Tailwind CSS Candidate Extractor
+///
+/// Core assumptions:
+/// - The extractor is intended to scan data that is valid UTF-8.
+/// - Scanning invalid UTF-8 may result in incorrect output.
+/// - No code should **ever** panic even in the presence of invalid data.
+///
+/// The extractor is designed to operate on a tuple of two pieces of data:
+/// - The current state
+/// - The current byte
+///
+/// A byte-to-fn-pointer table is used per-state such that the CPU can
+/// accurately predict upcoming branches. This is a critical optimization
+/// that allows the extractor to run at maximum speed without requiring
+/// SIMD-like parallelism for every operation.
+///
+
+/// This represents the current "state" of the extractor.
+enum ParseState {
+  Start,
+  Candidate,
+  Arbitrary,
+}
+
+
+// Enter arbitrary value mode
+// b'[' => {
+//     trace!("Arbitrary::Start\t");
+//     self.in_arbitrary = true;
+//     self.idx_arbitrary_start = self.cursor.pos;
+
+//     ParseAction::Consume
+// }
+
+// // Allowed first characters.
+// b'@' | b'!' | b'-' | b'<' | b'>' | b'0'..=b'9' | b'a'..=b'z' | b'A'..=b'Z' | b'*' => {
+//     // TODO: A bunch of characters that we currently support but maybe we only want it behind
+//     // a flag. E.g.: `<sm`
+//     // | '$' | '^' | '_'
+
+//     // When the new candidate is preceded by a `:`, then we want to keep parsing, but
+//     // throw away the full candidate because it can not be a valid candidate at the end
+//     // of the day.
+//     if self.cursor.prev == b':' {
+//         self.discard_next = true;
+//     }
+
+//     trace!("Candidate::Start\t");
+
+//     ParseAction::Consume
+// }
+
+// const TABLE_START: [TableCaseStart; 256] = {
+//   //
+// };
+
+// static __CASES: [Case; 256] = {
+//   let mut cases = [Case::Other; 256];
+
+//   cases[0x00] = Case::Nul;
+
+//   let mut i = 0x01;
+//   while i <= 0x1f {
+//     cases[i] = Case::Control;
+//     i+=1;
+//   }
+
+//   cases[0x7f] = Case::Control;
+
+//   let mut i = b'0';
+//   while i <= b'9' {
+//     cases[i as usize] = Case::Ident;
+//     i+=1;
+//   }
+
+//   let mut i = b'A';
+//   while i <= b'Z' {
+//     cases[i as usize] = Case::Ident;
+//     i+=1;
+//   }
+
+//   let mut i = b'a';
+//   while i <= b'z' {
+//     cases[i as usize] = Case::Ident;
+//     i+=1;
+//   }
+
+//   cases[b'-' as usize] = Case::Ident;
+//   cases[b'_' as usize] = Case::Ident;
+
+//   let mut i = 0x80;
+//   while i <= 0xff {
+//     cases[i] = Case::Ident;
+//     i+=1;
+//   }
+
+//   cases
+// };
+
+
+// #[inline(always)]
+// fn parse_char(&mut self) -> ParseAction<'a> {
+//     if self.in_arbitrary {
+//         self.parse_arbitrary()
+//     } else if self.in_candidate {
+//         self.parse_continue()
+//     } else if self.parse_start() == ParseAction::Consume {
+//         self.in_candidate = true;
+//         self.idx_start = self.cursor.pos;
+//         self.idx_end = self.cursor.pos;
+
+//         ParseAction::Consume
+//     } else {
+//         ParseAction::Skip
+//     }
+// }

crates/oxide/src/fast_skip.rs

@@ -80,10 +80,10 @@ fn is_ascii_whitespace(value: [u8; STRIDE]) -> [bool; STRIDE] {
     let whitespace_5 = eq(value, b' ');
 
     or(
-        or(
-            or(or(whitespace_1, whitespace_2), whitespace_3),
-            whitespace_4,
-        ),
-        whitespace_5,
+      or(
+        or(whitespace_1, whitespace_2),
+        or(whitespace_3, whitespace_4)
+      ),
+      whitespace_5
     )
 }

crates/oxide/src/lib.rs

@@ -16,6 +16,7 @@ pub mod fast_skip;
 pub mod glob;
 pub mod parser;
 pub mod scanner;
+pub mod extractor;
 
 static SHOULD_TRACE: sync::LazyLock<bool> = sync::LazyLock::new(
     || matches!(std::env::var("DEBUG"), Ok(value) if value.eq("*") || value.eq("1") || value.eq("true") || value.contains("tailwind")),

crates/plugin-example/Cargo.toml

@@ -0,0 +1,15 @@
+[package]
+name = "tailwindcss-plugin-example"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+lsp-server = "0.7.6"
+serde = "1.0.209"
+serde_json = "1.0.127"
+tracing = "0.1.40"
+tailwindcss-core = { path = "../core" }
+crossbeam-channel = "0.5.13"
+log = "0.4.22"
+tokio = { version = "1.39.3", features = ["full"] }
+mio = "1.0.2"

crates/plugin-example/node/package-lock.json

@@ -0,0 +1,58 @@
+{
+  "name": "node",
+  "version": "1.0.0",
+  "lockfileVersion": 3,
+  "requires": true,
+  "packages": {
+    "": {
+      "name": "node",
+      "version": "1.0.0",
+      "license": "ISC",
+      "dependencies": {
+        "vscode-jsonrpc": "^8.2.1",
+        "vscode-languageserver": "^9.0.1"
+      }
+    },
+    "node_modules/vscode-jsonrpc": {
+      "version": "8.2.1",
+      "resolved": "https://registry.npmjs.org/vscode-jsonrpc/-/vscode-jsonrpc-8.2.1.tgz",
+      "integrity": "sha512-kdjOSJ2lLIn7r1rtrMbbNCHjyMPfRnowdKjBQ+mGq6NAW5QY2bEZC/khaC5OR8svbbjvLEaIXkOq45e2X9BIbQ==",
+      "engines": {
+        "node": ">=14.0.0"
+      }
+    },
+    "node_modules/vscode-languageserver": {
+      "version": "9.0.1",
+      "resolved": "https://registry.npmjs.org/vscode-languageserver/-/vscode-languageserver-9.0.1.tgz",
+      "integrity": "sha512-woByF3PDpkHFUreUa7Hos7+pUWdeWMXRd26+ZX2A8cFx6v/JPTtd4/uN0/jB6XQHYaOlHbio03NTHCqrgG5n7g==",
+      "dependencies": {
+        "vscode-languageserver-protocol": "3.17.5"
+      },
+      "bin": {
+        "installServerIntoExtension": "bin/installServerIntoExtension"
+      }
+    },
+    "node_modules/vscode-languageserver-protocol": {
+      "version": "3.17.5",
+      "resolved": "https://registry.npmjs.org/vscode-languageserver-protocol/-/vscode-languageserver-protocol-3.17.5.tgz",
+      "integrity": "sha512-mb1bvRJN8SVznADSGWM9u/b07H7Ecg0I3OgXDuLdn307rl/J3A9YD6/eYOssqhecL27hK1IPZAsaqh00i/Jljg==",
+      "dependencies": {
+        "vscode-jsonrpc": "8.2.0",
+        "vscode-languageserver-types": "3.17.5"
+      }
+    },
+    "node_modules/vscode-languageserver-protocol/node_modules/vscode-jsonrpc": {
+      "version": "8.2.0",
+      "resolved": "https://registry.npmjs.org/vscode-jsonrpc/-/vscode-jsonrpc-8.2.0.tgz",
+      "integrity": "sha512-C+r0eKJUIfiDIfwJhria30+TYWPtuHJXHtI7J0YlOmKAo7ogxP20T0zxB7HZQIFhIyvoBPwWskjxrvAtfjyZfA==",
+      "engines": {
+        "node": ">=14.0.0"
+      }
+    },
+    "node_modules/vscode-languageserver-types": {
+      "version": "3.17.5",
+      "resolved": "https://registry.npmjs.org/vscode-languageserver-types/-/vscode-languageserver-types-3.17.5.tgz",
+      "integrity": "sha512-Ld1VelNuX9pdF39h2Hgaeb5hEZM2Z3jUrrMgWQAu82jMtZp7p3vJT3BzToKtZI7NgQssZje5o0zryOrhQvzQAg=="
+    }
+  }
+}

crates/plugin-example/node/package.json

@@ -0,0 +1,15 @@
+{
+  "name": "node",
+  "version": "1.0.0",
+  "main": "index.js",
+  "scripts": {
+    "test": "echo \"Error: no test specified\" && exit 1"
+  },
+  "author": "",
+  "license": "ISC",
+  "description": "",
+  "dependencies": {
+    "vscode-jsonrpc": "^8.2.1",
+    "vscode-languageserver": "^9.0.1"
+  }
+}

crates/plugin-example/node/src/client.ts

@@ -0,0 +1,14 @@
+import * as net from 'node:net'
+import * as rpc from 'vscode-jsonrpc/node'
+
+let client = net.connect(12345)
+
+// Use stdin and stdout for communication:
+let connection = rpc.createMessageConnection(client, client)
+
+connection.onNotification('loaded', () => console.log('server loaded'))
+connection.onNotification('ping', () => console.log('ping'))
+connection.onNotification('@/plugins/loaded', () => console.log('plugins loaded'))
+
+connection.listen()
+connection.sendRequest('@/plugins/load', 'foo')

crates/plugin-example/node/src/plugin-api.ts

@@ -0,0 +1,127 @@
+export type PluginFn = (api: PluginAPI) => void
+export type PluginWithConfig = { handler: PluginFn }
+export type PluginWithOptions<T> = {
+  (options?: T): PluginWithConfig
+  __isOptionsFunction: true
+}
+
+export type Plugin = PluginFn | PluginWithConfig | PluginWithOptions<any>
+export type CssInJs = { [key: string]: string | CssInJs | CssInJs[] }
+
+export type NamedUtilityValue = {
+  kind: 'named'
+
+  /**
+   * bg-red-500
+   *    ^^^^^^^
+   *
+   * w-1/2
+   *   ^
+   */
+  value: string
+
+  /**
+   * w-1/2
+   *   ^^^
+   */
+  fraction: string | null
+}
+
+export type PluginAPI = {
+  addBase(base: CssInJs): void
+  addVariant(name: string, variant: string | string[] | CssInJs): void
+
+  addUtilities(
+    utilities: Record<string, CssInJs | CssInJs[]> | Record<string, CssInJs | CssInJs[]>[],
+    options?: {},
+  ): void
+
+  matchUtilities(
+    utilities: Record<
+      string,
+      (value: string, extra: { modifier: string | null }) => CssInJs | CssInJs[]
+    >,
+    options?: Partial<{
+      type: string | string[]
+      supportsNegativeValues: boolean
+      values: Record<string, string> & {
+        __BARE_VALUE__?: (value: NamedUtilityValue) => string | undefined
+      }
+      modifiers: 'any' | Record<string, string>
+    }>,
+  ): void
+
+  // addComponents(utilities: Record<string, CssInJs> | Record<string, CssInJs>[], options?: {}): void
+  // matchComponents(
+  //   utilities: Record<string, (value: string, extra: { modifier: string | null }) => CssInJs>,
+  //   options?: Partial<{
+  //     type: string | string[]
+  //     supportsNegativeValues: boolean
+  //     values: Record<string, string> & {
+  //       __BARE_VALUE__?: (value: NamedUtilityValue) => string | undefined
+  //     }
+  //     modifiers: 'any' | Record<string, string>
+  //   }>,
+  // ): void
+
+  // theme(path: string, defaultValue?: any): any
+  // prefix(className: string): string
+}
+
+import * as rpc from 'vscode-jsonrpc/node'
+
+export function buildPluginController(server: rpc.MessageConnection) {
+  let utilityMap = new Map<
+    string,
+    (value: string, extra: { modifier: string | null }) => CssInJs | CssInJs[]
+  >()
+
+  let api = buildPluginApi(server, utilityMap)
+
+  return {
+    api,
+
+    matchUtility(id: string, value: string, modifier: string | null) {
+      let fn = utilityMap.get(id)
+      if (!fn) return
+
+      return fn(value, { modifier })
+    },
+  }
+}
+
+function buildPluginApi(
+  server: rpc.MessageConnection,
+  utilityMap: Map<
+    string,
+    (value: string, extra: { modifier: string | null }) => CssInJs | CssInJs[]
+  >,
+): PluginAPI {
+  return {
+    addBase(base) {
+      server.sendNotification('@/plugin/add-base', { ast: base })
+    },
+
+    addVariant(name, variant) {
+      server.sendNotification('@/plugin/add-variant', { name, format: variant })
+    },
+
+    addUtilities(utilities, options) {
+      server.sendNotification('@/plugin/add-utilities', { ast: utilities, options })
+    },
+
+    matchUtilities(utilities, options) {
+      let namesToIds: Record<string, string> = {}
+
+      for (let [name, fn] of Object.entries(utilities)) {
+        let id = Math.random().toString(36).slice(2)
+        namesToIds[name] = id
+        utilityMap.set(id, fn)
+      }
+
+      server.sendNotification('@/plugin/match-utility', {
+        utilities: namesToIds,
+      })
+    },
+  }
+}

crates/plugin-example/node/src/plugin.ts

@@ -0,0 +1,27 @@
+import type { PluginAPI } from './plugin-api'
+
+module.exports = function ({ addBase, addVariant, addUtilities, matchUtilities }: PluginAPI) {
+  addBase({
+    div: {
+      transform: 'skewY(-10deg)',
+    },
+  })
+
+  addVariant('hover', ':hover')
+  addVariant('marker', ['::marker', '* ::marker'])
+
+  addUtilities({
+    '.skew-10deg': {
+      transform: 'skewY(-10deg)',
+    },
+  })
+
+  matchUtilities(
+    { skew: (value) => ({ transform: `skewY(${value})` }) },
+    {
+      values: {
+        f10: '10deg',
+      },
+    },
+  )
+}

crates/plugin-example/node/src/server.ts

@@ -0,0 +1,33 @@
+import * as net from 'node:net'
+import * as rpc from 'vscode-jsonrpc/node'
+import { buildPluginController, PluginFn } from './plugin-api'
+
+let socket = await new Promise<net.Socket>((resolve) => {
+  net.createServer(resolve).listen(12345)
+})
+
+let server = rpc.createMessageConnection(socket, socket)
+let controller = buildPluginController(server)
+
+async function loadPlugin(path: string): Promise<PluginFn> {
+  return import(path).then((m) => m.default ?? m)
+}
+
+server.onRequest('@/plugins/load', async ({ plugins: paths }) => {
+  console.log('Loading…')
+  let plugins: PluginFn[] = await Promise.all(paths.map(loadPlugin))
+
+  for (let plugin of plugins) {
+    plugin(controller.api)
+  }
+  console.log('Loaded…')
+})
+
+server.onRequest('@/plugins/match-utility', async ({ id, value, modifier }) => {
+  let ast = controller.matchUtility(id, value, modifier)
+
+  return { ast }
+})
+
+server.listen()
+server.sendNotification('loaded')

crates/plugin-example/src/app.rs

@@ -0,0 +1,111 @@
+use std::{collections::HashMap, error::Error};
+
+use lsp_server::{Connection, Message, Notification, ReqQueue, Request, RequestId, Response};
+use serde_json::Value;
+use tokio::sync::oneshot;
+
+type AppResult<T> = Result<T, Box<dyn Error + Sync + Send>>;
+type ReqHandler = Box<dyn Fn(&mut App, Response) -> ()>;
+
+pub struct App {
+  connection: Connection,
+  queue: ReqQueue::<usize, ReqHandler>,
+  utilities: HashMap::<String, Vec<String>>,
+}
+
+impl App {
+  pub fn new(connection: Connection) -> Self {
+    Self {
+      connection,
+      queue: ReqQueue::default(),
+      utilities: HashMap::new(),
+    }
+  }
+
+  pub async fn main_loop(&mut self) -> AppResult<()> {
+    for msg in self.connection.receiver.clone() {
+      match msg {
+        Message::Request(req) => self.on_request(req).await?,
+        Message::Response(res) => self.on_response(res).await?,
+        Message::Notification(note) => self.on_note(note).await?,
+        _ => {},
+      };
+    }
+
+    Ok(())
+  }
+
+  async fn on_request(&mut self, req: Request) -> AppResult<()> {
+    //
+    Ok(())
+  }
+
+  async fn on_response(&mut self, res: Response) -> AppResult<()> {
+    self.queue.outgoing.complete(res.id);
+
+    Ok(())
+  }
+
+  async fn on_note(&mut self, note: Notification) -> AppResult<()> {
+    match &note.method[..] {
+      "@/plugin/match-utility" => {
+        self.on_match_utility(note.params)?;
+      },
+      _ => {},
+    };
+
+    Ok(())
+  }
+
+  pub async fn load_plugins(&mut self, paths: Vec<String>) -> AppResult<()> {
+    let (tx, rx) = oneshot::channel::<usize>();
+
+    let request = self.queue.outgoing.register(
+      "@/plugins/load".to_owned(),
+      serde_json::json!({
+        "plugins": paths,
+      }),
+      Box::new(move |app, res| {
+        tx.send(0).unwrap();
+      })
+    );
+
+    let id = request.id.clone();
+
+    self.connection.sender.send(Message::Request(request))?;
+
+    rx.await?;
+
+    Ok(())
+  }
+
+  fn on_match_utility(&mut self, params: Value) -> AppResult<()> {
+    let params = params["utilities"].as_object().unwrap();
+
+    for (key, value) in params {
+      let id = value.as_str().unwrap().to_owned();
+
+      self.utilities.entry(key.clone()).or_default().push(id);
+    }
+
+    Ok(())
+  }
+
+  pub async fn call_match_utility(&mut self, name: &str, value: &str) -> AppResult<()> {
+    let utility_id = self.utilities.get(name).unwrap().first().unwrap().clone();
+
+    let request = self.queue.outgoing.register(
+      "@/plugins/match-utility".to_owned(),
+      serde_json::json!({
+        "id": utility_id,
+        "value": value,
+        "modifier": null,
+      }),
+      0
+    );
+
+    self.connection.sender.send(Message::Request(request))?;
+
+    Ok(())
+  }
+}

crates/plugin-example/src/main.rs

@@ -0,0 +1,73 @@
+mod app;
+mod pipes;
+
+use std::{collections::HashMap, error::Error, net::SocketAddr, process::{Command, Stdio}, thread, time::Duration};
+
+use app::App;
+use lsp_server::{Connection, Message, ReqQueue, Request};
+use tailwindcss_css::ast::{rule, AstNode, WalkAction};
+
+#[tokio::main]
+async fn main() -> Result<(), Box<dyn Error + Sync + Send>> {
+  let mut ast: Vec<AstNode> = vec![
+    rule(b"@plugin \"./plugin.ts\"".to_vec(), vec![]),
+  ];
+
+  // 1. Collect paths of all plugins in the CSS
+  let mut plugins_paths: Vec<String> = vec![];
+
+  for node in ast.iter_mut() {
+    node.walk(&mut |node, _| {
+      let AstNode::Rule { selector, .. } = node else {
+        return WalkAction::Continue;
+      };
+
+      if !selector.starts_with(b"@plugin") {
+        return WalkAction::Continue;
+      }
+
+      let path = selector.split_at(7).1;
+      let path = &path[2..path.len()-1];
+      let path = path.to_vec();
+
+      plugins_paths.push(unsafe {
+        String::from_utf8_unchecked(path)
+      });
+
+      WalkAction::Continue
+    });
+  }
+
+  // 2. Spawn node server
+  let mut node_server = Command::new("bun")
+      .args(["node/src/server.ts"])
+      .stdin(Stdio::inherit())
+      .stdout(Stdio::inherit())
+      .spawn()
+      .unwrap();
+
+  // 3. Wait for the server to start
+  thread::sleep(Duration::from_millis(500));
+
+  let (conn, io_threads) = Connection::connect("127.0.0.1:12345".parse::<SocketAddr>()?)?;
+
+  let mut app = App::new(conn);
+
+  _ = app.main_loop().await;
+
+  // 4. Load Plugins
+  app.load_plugins(plugins_paths).await?;
+
+  // 6. Ask server to match utilities
+  app.call_match_utility("skew", "f10").await?;
+
+  // 7. Wait for the server to respond
+  thread::sleep(Duration::from_millis(100));
+
+  // 7. Update the AST with the matched utilities
+
+  io_threads.join()?;
+  node_server.kill()?;
+
+  Ok(())
+}

crates/plugin-example/src/pipes.rs

@@ -0,0 +1,79 @@
+use std::{
+    io::{self, stdin, stdout, BufReader, BufWriter, Write}, process::{Child, ChildStdin, ChildStdout}, thread
+};
+
+use log::debug;
+
+use crossbeam_channel::{bounded, Receiver, Sender};
+use lsp_server::Message;
+
+/// Creates an LSP connection via stdio.
+pub fn process_transport(
+  child: &mut Child,
+) -> (Sender<Message>, Receiver<Message>, IoThreads) {
+  let stdout = child.stdin.take().expect("failed to get child stdin");
+  let stdin = child.stdout.take().expect("failed to get child stdout");
+
+  pipes_transport(stdout, stdin)
+}
+
+/// Creates an LSP connection via stdio.
+pub fn pipes_transport(
+  stdout: ChildStdin,
+  stdin: ChildStdout,
+) -> (Sender<Message>, Receiver<Message>, IoThreads) {
+    // Send messages to the child process
+    let mut writer = stdout;
+    let (writer_sender, writer_receiver) = bounded::<Message>(0);
+    let writer = thread::spawn(move || {
+        writer_receiver.into_iter().try_for_each(|it| it.write(&mut writer))
+    });
+
+    // Recieve messages from the child process
+    let mut reader = BufReader::with_capacity(1, stdin);
+    let (reader_sender, reader_receiver) = bounded::<Message>(0);
+    let reader = thread::spawn(move || {
+        loop {
+            let Some(msg) = Message::read(&mut reader)? else {
+              break;
+            };
+
+            let is_exit = matches!(&msg, Message::Notification(n) if n.method == "exit");
+
+            debug!("sending message {:#?}", msg);
+            reader_sender.send(msg).expect("receiver was dropped, failed to send a message");
+
+            if is_exit {
+                break;
+            }
+        }
+        Ok(())
+    });
+
+    let threads = IoThreads { reader, writer };
+    (writer_sender, reader_receiver, threads)
+}
+
+pub struct IoThreads {
+    reader: thread::JoinHandle<io::Result<()>>,
+    writer: thread::JoinHandle<io::Result<()>>,
+}
+
+impl IoThreads {
+    pub fn join(self) -> io::Result<()> {
+        match self.reader.join() {
+            Ok(r) => r?,
+            Err(err) => {
+                println!("reader panicked!");
+                std::panic::panic_any(err)
+            }
+        }
+        match self.writer.join() {
+            Ok(r) => r,
+            Err(err) => {
+                println!("writer panicked!");
+                std::panic::panic_any(err);
+            }
+        }
+    }
+}

packages/tailwindcss/src/css-parser.test.ts

@@ -1,5 +1,6 @@
 import { describe, expect, it } from 'vitest'
 import * as CSS from './css-parser'
+import { segment } from './utils/segment'
 
 const css = String.raw
 
@@ -1036,3 +1037,49 @@ describe.each(['Unix', 'Windows'])('Line endings: %s', (lineEndings) => {
     })
   })
 })
+
+it.only('wip css-parser on preflight.css', async () => {
+  const { fileURLToPath } = await import('node:url')
+  const { readFile } = await import('node:fs/promises')
+  const currentFolder = fileURLToPath(new URL('..', import.meta.url))
+  const cssFile = await readFile(currentFolder + './preflight.css', 'utf-8')
+
+  function formatByteSize(size: number) {
+    const units = ['B', 'KB', 'MB', 'GB', 'TB', 'PB', 'EB', 'ZB', 'YB']
+    const unit = 1000
+    let i = 0
+    while (size > unit) {
+      size /= unit
+      i++
+    }
+    return `${size.toFixed(2)} ${units[i]}`
+  }
+
+  function throughput(iterations: number, memoryBaseline: number, callback: () => void) {
+    let now = process.hrtime.bigint()
+    let len = 0
+    for (let i = 0; i < iterations; ++i) {
+      len += CSS.parse(cssFile).length
+    }
+    let elapsed = Number(process.hrtime.bigint() - now) / 1e9
+    let memorySize = iterations * memoryBaseline
+    let rate = memorySize / elapsed
+
+    return { rate, elapsed, len }
+  }
+
+  let t1 = throughput(100_000, cssFile.length, () => CSS.parse(cssFile).length)
+  console.log(`CSS.parse: ${formatByteSize(t1.rate)}/s over ${t1.elapsed}s`)
+
+  let input =
+    'var(--a, 0 0 1px rgb(0, 0, 0)), 0 0 1px rgb(0, 0, 0), var(--a, 0 0 1px rgb(0, 0, 0)), 0 0 1px rgb(0, 0, 0), '.repeat(
+      500,
+    )
+
+  let t2 = throughput(100_000, input.length, () => segment(input, ','))
+  console.log(`segment: ${formatByteSize(t2.rate)}/s over ${t2.elapsed}s`)
+
+  console.log({ t1, t2 })
+
+  throw new Error('stop here')
+})

rust-toolchain.toml

@@ -1,3 +1,3 @@
 [toolchain]
-channel = "1.80.1"
+channel = "1.81"
 profile = "default"