Detect classes in markdown inline directives (#18967)

Fixes #18071

CHANGELOG.md

@@ -24,6 +24,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Show Lightning CSS warnings (if any) when optimizing/minifying ([#18918](https://github.com/tailwindlabs/tailwindcss/pull/18918))
 - Use `default` export condition for `@tailwindcss/vite` ([#18948](https://github.com/tailwindlabs/tailwindcss/pull/18948))
 - 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))
 
 ## [4.1.13] - 2025-09-03
 

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

@@ -0,0 +1,63 @@
+use crate::cursor;
+use crate::extractor::pre_processors::pre_processor::PreProcessor;
+
+#[derive(Debug, Default)]
+pub struct Markdown;
+
+impl PreProcessor for Markdown {
+    fn process(&self, content: &[u8]) -> Vec<u8> {
+        let len = content.len();
+        let mut result = content.to_vec();
+        let mut cursor = cursor::Cursor::new(content);
+
+        let mut in_directive = false;
+
+        while cursor.pos < len {
+            match (in_directive, cursor.curr) {
+                (false, b'{') => {
+                    result[cursor.pos] = b' ';
+                    in_directive = true;
+                }
+                (true, b'}') => {
+                    result[cursor.pos] = b' ';
+                    in_directive = false;
+                }
+                (true, b'.') => {
+                    result[cursor.pos] = b' ';
+                }
+                _ => {}
+            }
+
+            cursor.advance();
+        }
+
+        result
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::Markdown;
+    use crate::extractor::pre_processors::pre_processor::PreProcessor;
+
+    #[test]
+    fn test_markdown_pre_processor() {
+        for (input, expected) in [
+            // Convert dots to spaces inside markdown inline directives
+            (
+                ":span[Some Text]{.text-gray-500}",
+                ":span[Some Text]  text-gray-500 ",
+            ),
+            (
+                ":span[Some Text]{.text-gray-500.bg-red-500}",
+                ":span[Some Text]  text-gray-500 bg-red-500 ",
+            ),
+            (
+                ":span[Some Text]{#myId .my-class key=val key2='val 2'}",
+                ":span[Some Text] #myId  my-class key=val key2='val 2' ",
+            ),
+        ] {
+            Markdown::test(input, expected);
+        }
+    }
+}

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

@@ -2,6 +2,7 @@ pub mod clojure;
 pub mod elixir;
 pub mod haml;
 pub mod json;
+pub mod markdown;
 pub mod pre_processor;
 pub mod pug;
 pub mod razor;
@@ -14,6 +15,7 @@ pub use clojure::*;
 pub use elixir::*;
 pub use haml::*;
 pub use json::*;
+pub use markdown::*;
 pub use pre_processor::*;
 pub use pug::*;
 pub use razor::*;

crates/oxide/src/scanner/mod.rs

@@ -486,6 +486,7 @@ pub fn pre_process_input(content: &[u8], extension: &str) -> Vec<u8> {
         "cshtml" | "razor" => Razor.process(content),
         "haml" => Haml.process(content),
         "json" => Json.process(content),
+        "md" | "mdx" => Markdown.process(content),
         "pug" => Pug.process(content),
         "rb" | "erb" => Ruby.process(content),
         "slim" | "slang" => Slim.process(content),