Detect classes inside Elixir charlist, word list, and string sigils (#18432)

Fixes #18431

The `~W(…)` syntax in Elixir is a _sigil_. It's basically another way to
write strings, arrays of strings, etc… The syntax lets you use a handful
of surrounding brackets like `~W(…)`, `~W[…]`, `~W{…}`, `~W"…"`, etc… to
let you write lists without necessarily having to escape characters.

In v3 our extractor was able to pick these up but in v4 Oxide does not.
I've added a preprocessor for Elixir files so we can modify the code
before our main extractor sees it.

Now things like this: `~W(text-white bg-gray-600)` will get turned into
` ~W text-white bg-gray-600 ` which can easily be processed by our
extractor.

The sigils we support are:
- `~s` / `~S` (strings)
- `~w` / `~W` (word lists)
- `~c` / `~C` (charlists)

We're specifically detecting the use of `(…)`, `[…]`, and `{…}` as using
quotes already works today.

---------

Co-authored-by: Robin Malfait <malfait.robin@gmail.com>

CHANGELOG.md

@@ -11,6 +11,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Don't consider the global important state in `@apply` ([#18404](https://github.com/tailwindlabs/tailwindcss/pull/18404))
 - Fix trailing `)` from interfering with extraction in Clojure keywords ([#18345](https://github.com/tailwindlabs/tailwindcss/pull/18345))
+- Detect classes inside Elixir charlist, word list, and string sigils ([#18432](https://github.com/tailwindlabs/tailwindcss/pull/18432))
 
 ## [4.1.11] - 2025-06-26
 

crates/oxide/src/extractor/mod.rs

@@ -1058,10 +1058,7 @@ mod tests {
     #[test]
     fn test_leptos_rs_view_class_colon_syntax() {
         for (input, expected) in [
-            (
-                r#"<div class:px-6=true>"#,
-                vec!["class", "px-6"],
-            ),
+            (r#"<div class:px-6=true>"#, vec!["class", "px-6"]),
             (
                 r#"view! { <div class:px-6=true> }"#,
                 vec!["class", "px-6", "view!"],

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

@@ -16,10 +16,10 @@ pub struct Clojure;
 /// can simplify this list quite a bit.
 #[inline]
 fn is_keyword_character(byte: u8) -> bool {
-    return matches!(
+    (matches!(
         byte,
         b'!' | b'#' | b'%' | b'*' | b'+' | b'-' | b'.' | b'/' | b':' | b'_'
-    ) | byte.is_ascii_alphanumeric();
+    ) | byte.is_ascii_alphanumeric())
 }
 
 impl PreProcessor for Clojure {

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

@@ -0,0 +1,154 @@
+use crate::cursor;
+use crate::extractor::bracket_stack::BracketStack;
+use crate::extractor::pre_processors::pre_processor::PreProcessor;
+
+#[derive(Debug, Default)]
+pub struct Elixir;
+
+impl PreProcessor for Elixir {
+    fn process(&self, content: &[u8]) -> Vec<u8> {
+        let mut cursor = cursor::Cursor::new(content);
+        let mut result = content.to_vec();
+        let mut bracket_stack = BracketStack::default();
+
+        while cursor.pos < content.len() {
+            // Look for a sigil marker
+            if cursor.curr != b'~' {
+                cursor.advance();
+                continue;
+            }
+
+            // Scan charlists, strings, and wordlists
+            if !matches!(cursor.next, b'c' | b'C' | b's' | b'S' | b'w' | b'W') {
+                cursor.advance();
+                continue;
+            }
+
+            cursor.advance_twice();
+
+            // Match the opening for a sigil
+            if !matches!(cursor.curr, b'(' | b'[' | b'{') {
+                continue;
+            }
+
+            // Replace the opening bracket with a space
+            result[cursor.pos] = b' ';
+
+            // Scan until we find a balanced closing one and replace it too
+            bracket_stack.push(cursor.curr);
+
+            while cursor.pos < content.len() {
+                cursor.advance();
+
+                match cursor.curr {
+                    // Escaped character, skip ahead to the next character
+                    b'\\' => cursor.advance_twice(),
+                    b'(' | b'[' | b'{' => {
+                        bracket_stack.push(cursor.curr);
+                    }
+                    b')' | b']' | b'}' if !bracket_stack.is_empty() => {
+                        bracket_stack.pop(cursor.curr);
+
+                        if bracket_stack.is_empty() {
+                            // Replace the closing bracket with a space
+                            result[cursor.pos] = b' ';
+                            break;
+                        }
+                    }
+                    _ => {}
+                }
+            }
+        }
+
+        result
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::Elixir;
+    use crate::extractor::pre_processors::pre_processor::PreProcessor;
+
+    #[test]
+    fn test_elixir_pre_processor() {
+        for (input, expected) in [
+            // Simple sigils
+            ("~W(flex underline)", "~W flex underline "),
+            ("~W[flex underline]", "~W flex underline "),
+            ("~W{flex underline}", "~W flex underline "),
+            // Sigils with nested brackets
+            (
+                "~W(text-(--my-color) bg-(--my-color))",
+                "~W text-(--my-color) bg-(--my-color) ",
+            ),
+            ("~W[text-[red] bg-[red]]", "~W text-[red] bg-[red] "),
+            // Word sigils with modifiers
+            ("~W(flex underline)a", "~W flex underline a"),
+            ("~W(flex underline)c", "~W flex underline c"),
+            ("~W(flex underline)s", "~W flex underline s"),
+            // Other sigil types
+            ("~w(flex underline)", "~w flex underline "),
+            ("~c(flex underline)", "~c flex underline "),
+            ("~C(flex underline)", "~C flex underline "),
+            ("~s(flex underline)", "~s flex underline "),
+            ("~S(flex underline)", "~S flex underline "),
+        ] {
+            Elixir::test(input, expected);
+        }
+    }
+
+    #[test]
+    fn test_extract_candidates() {
+        let input = r#"
+          ~W(c1 c2)
+          ~W[c3 c4]
+          ~W{c5 c6}
+          ~W(text-(--c7) bg-(--c8))
+          ~W[text-[c9] bg-[c10]]
+          ~W(c13 c14)a
+          ~W(c15 c16)c
+          ~W(c17 c18)s
+          ~w(c19 c20)
+          ~c(c21 c22)
+          ~C(c23 c24)
+          ~s(c25 c26)
+          ~S(c27 c28)
+          ~W"c29 c30"
+          ~W'c31 c32'
+        "#;
+
+        Elixir::test_extract_contains(
+            input,
+            vec![
+                "c1",
+                "c2",
+                "c3",
+                "c4",
+                "c5",
+                "c6",
+                "text-(--c7)",
+                "bg-(--c8)",
+                "c13",
+                "c14",
+                "c15",
+                "c16",
+                "c17",
+                "c18",
+                "c19",
+                "c20",
+                "c21",
+                "c22",
+                "c23",
+                "c24",
+                "c25",
+                "c26",
+                "c27",
+                "c28",
+                "c29",
+                "c30",
+                "c31",
+                "c32",
+            ],
+        );
+    }
+}

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

@@ -1,4 +1,5 @@
 pub mod clojure;
+pub mod elixir;
 pub mod haml;
 pub mod json;
 pub mod pre_processor;
@@ -10,6 +11,7 @@ pub mod svelte;
 pub mod vue;
 
 pub use clojure::*;
+pub use elixir::*;
 pub use haml::*;
 pub use json::*;
 pub use pre_processor::*;

crates/oxide/src/scanner/mod.rs

@@ -482,6 +482,7 @@ pub fn pre_process_input(content: &[u8], extension: &str) -> Vec<u8> {
 
     match extension {
         "clj" | "cljs" | "cljc" => Clojure.process(content),
+        "heex" | "eex" | "ex" | "exs" => Elixir.process(content),
         "cshtml" | "razor" => Razor.process(content),
         "haml" => Haml.process(content),
         "json" => Json.process(content),