Add Maud templating support (#18988)

This PR adds support for Maud templates in Rust.

We already had some pre-processing for Rust but for Leptos `class:`
syntax. This PR now added a dedicated Rust pre-processor that handles
Leptos and Maud syntax.

We only start pre-processing Maud templates if the Rust file includes
the `html!` macro.

## Test plan

Looking at the extractor, you can see that we now do extract the proper
classes in Maud templates:

<img width="1076" height="1856" alt="image"
src="https://github.com/user-attachments/assets/e649e1de-289e-466f-8fab-44a938a47dd5"
/>


Fixes: #18984

CHANGELOG.md

@@ -26,6 +26,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Re-throw errors from PostCSS nodes ([#18373](https://github.com/tailwindlabs/tailwindcss/pull/18373))
 - Detect classes in markdown inline directives ([#18967](https://github.com/tailwindlabs/tailwindcss/pull/18967))
 - Ensure files with only `@theme` produce no output when built ([#18979](https://github.com/tailwindlabs/tailwindcss/pull/18979))
+- Support Maud templates when extracting classes ([#18988](https://github.com/tailwindlabs/tailwindcss/pull/18988))
 
 ## [4.1.13] - 2025-09-03
 

crates/oxide/src/extractor/pre_processors/mod.rs

@@ -7,6 +7,7 @@ pub mod pre_processor;
 pub mod pug;
 pub mod razor;
 pub mod ruby;
+pub mod rust;
 pub mod slim;
 pub mod svelte;
 pub mod vue;
@@ -20,6 +21,7 @@ pub use pre_processor::*;
 pub use pug::*;
 pub use razor::*;
 pub use ruby::*;
+pub use rust::*;
 pub use slim::*;
 pub use svelte::*;
 pub use vue::*;

crates/oxide/src/extractor/pre_processors/rust.rs

@@ -0,0 +1,216 @@
+use crate::extractor::bracket_stack;
+use crate::extractor::cursor;
+use crate::extractor::machine::Machine;
+use crate::extractor::pre_processors::pre_processor::PreProcessor;
+use crate::extractor::variant_machine::VariantMachine;
+use crate::extractor::MachineState;
+use bstr::ByteSlice;
+
+#[derive(Debug, Default)]
+pub struct Rust;
+
+impl PreProcessor for Rust {
+    fn process(&self, content: &[u8]) -> Vec<u8> {
+        // Leptos support: https://github.com/tailwindlabs/tailwindcss/pull/18093
+        let replaced_content = content
+            .replace(" class:", " class ")
+            .replace("\tclass:", " class ")
+            .replace("\nclass:", " class ");
+
+        if replaced_content.contains_str(b"html!") {
+            self.process_maud_templates(&replaced_content)
+        } else {
+            replaced_content
+        }
+    }
+}
+
+impl Rust {
+    fn process_maud_templates(&self, replaced_content: &[u8]) -> Vec<u8> {
+        let len = replaced_content.len();
+        let mut result = replaced_content.to_vec();
+        let mut cursor = cursor::Cursor::new(replaced_content);
+        let mut bracket_stack = bracket_stack::BracketStack::default();
+
+        while cursor.pos < len {
+            match cursor.curr {
+                // Escaped character, skip ahead to the next character
+                b'\\' => {
+                    cursor.advance_twice();
+                    continue;
+                }
+
+                // Consume strings as-is
+                b'"' => {
+                    result[cursor.pos] = b' ';
+                    cursor.advance();
+
+                    while cursor.pos < len {
+                        match cursor.curr {
+                            // Escaped character, skip ahead to the next character
+                            b'\\' => cursor.advance_twice(),
+
+                            // End of the string
+                            b'"' => {
+                                result[cursor.pos] = b' ';
+                                break;
+                            }
+
+                            // Everything else is valid
+                            _ => cursor.advance(),
+                        };
+                    }
+                }
+
+                // Only replace `.` with a space if it's not surrounded by numbers. E.g.:
+                //
+                // ```diff
+                // - .flex.items-center
+                // +  flex items-center
+                // ```
+                //
+                // But with numbers, it's allowed:
+                //
+                // ```diff
+                // - px-2.5
+                // + px-2.5
+                // ```
+                b'.' => {
+                    // Don't replace dots with spaces when inside of any type of brackets, because
+                    // this could be part of arbitrary values. E.g.: `bg-[url(https://example.com)]`
+                    //                                                                       ^
+                    if !bracket_stack.is_empty() {
+                        cursor.advance();
+                        continue;
+                    }
+
+                    // If the dot is surrounded by digits, we want to keep it. E.g.: `px-2.5`
+                    // EXCEPT if it's followed by a valid variant that happens to start with a
+                    // digit.
+                    // E.g.: `bg-red-500.2xl:flex`
+                    //                 ^^^
+                    if cursor.prev.is_ascii_digit() && cursor.next.is_ascii_digit() {
+                        let mut next_cursor = cursor.clone();
+                        next_cursor.advance();
+
+                        let mut variant_machine = VariantMachine::default();
+                        if let MachineState::Done(_) = variant_machine.next(&mut next_cursor) {
+                            result[cursor.pos] = b' ';
+                        }
+                    } else {
+                        result[cursor.pos] = b' ';
+                    }
+                }
+
+                b'[' => {
+                    bracket_stack.push(cursor.curr);
+                }
+
+                b']' if !bracket_stack.is_empty() => {
+                    bracket_stack.pop(cursor.curr);
+                }
+
+                // Consume everything else
+                _ => {}
+            };
+
+            cursor.advance();
+        }
+
+        result
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::Rust;
+    use crate::extractor::pre_processors::pre_processor::PreProcessor;
+
+    #[test]
+    fn test_leptos_extraction() {
+        for (input, expected) in [
+            // Spaces
+            (
+                "<div class:flex class:px-2.5={condition()}>",
+                "<div class flex class px-2.5={condition()}>",
+            ),
+            // Tabs
+            (
+                "<div\tclass:flex class:px-2.5={condition()}>",
+                "<div class flex class px-2.5={condition()}>",
+            ),
+            // Newlines
+            (
+                "<div\nclass:flex class:px-2.5={condition()}>",
+                "<div class flex class px-2.5={condition()}>",
+            ),
+        ] {
+            Rust::test(input, expected);
+        }
+    }
+
+    // https://github.com/tailwindlabs/tailwindcss/issues/18984
+    #[test]
+    fn test_maud_template_extraction() {
+        let input = r#"
+            use maud::{html, Markup};
+
+            pub fn main() -> Markup {
+                html! {
+                    header.px-8.py-4.text-black {
+                        "Hello, world!"
+                    }
+                }
+            }
+        "#;
+
+        Rust::test_extract_contains(input, vec!["px-8", "py-4", "text-black"]);
+
+        // https://maud.lambda.xyz/elements-attributes.html#classes-and-ids-foo-bar
+        let input = r#"
+            html! {
+                input #cannon .big.scary.bright-red type="button" value="Launch Party Cannon";
+            }
+        "#;
+        Rust::test_extract_contains(input, vec!["big", "scary", "bright-red"]);
+
+        let input = r#"
+            html! {
+                div."bg-[#0088cc]" { "Quotes for backticks" }
+            }
+        "#;
+        Rust::test_extract_contains(input, vec!["bg-[#0088cc]"]);
+
+        let input = r#"
+            html! {
+                #main {
+                    "Main content!"
+                    .tip { "Storing food in a refrigerator can make it 20% cooler." }
+                }
+            }
+        "#;
+        Rust::test_extract_contains(input, vec!["tip"]);
+
+        let input = r#"
+            html! {
+                div."bg-[url(https://example.com)]" { "Arbitrary values" }
+            }
+        "#;
+        Rust::test_extract_contains(input, vec!["bg-[url(https://example.com)]"]);
+
+        let input = r#"
+            html! {
+                div.px-4.text-black {
+                    "Some text, with unbalanced brackets ]["
+                }
+                div.px-8.text-white {
+                    "Some more text, with unbalanced brackets ]["
+                }
+            }
+        "#;
+        Rust::test_extract_contains(input, vec!["px-4", "text-black", "px-8", "text-white"]);
+
+        let input = r#"html! { \x.px-4.text-black {  } }"#;
+        Rust::test(input, r#"html! { \x px-4 text-black {  } }"#);
+    }
+}

crates/oxide/src/scanner/mod.rs

@@ -490,7 +490,8 @@ pub fn pre_process_input(content: &[u8], extension: &str) -> Vec<u8> {
         "pug" => Pug.process(content),
         "rb" | "erb" => Ruby.process(content),
         "slim" | "slang" => Slim.process(content),
-        "svelte" | "rs" => Svelte.process(content),
+        "svelte" => Svelte.process(content),
+        "rs" => Rust.process(content),
         "vue" => Vue.process(content),
         _ => content.to_vec(),
     }