Handle Ruby %w syntax in Slim pre processing (#17557)

This PR fixes an issue where the Ruby `%w[…]` syntax causes utilities to
not be properly extracted.

This PR will now ensure that it does get extracted correctly.

Given this input:
```slim
div[
  class=%w[bg-blue-500 w-10 h-10]
]
div[
  class=%w[w-10 bg-green-500 h-10]
]
```

Before this PR, we extracted everything but the `bg-blue-500`. The
`w-10` was extracted but not because of the second div, but because of
the first one.

Fixes: #17542

## Test plan

1. Added a test to ensure it's working correctly.

Looking at the extractor tool, you can see that it now gets extracted
correctly. Top is before, bottom is with this change.

<img width="1199" alt="image"
src="https://github.com/user-attachments/assets/028d9abd-8917-438c-a423-88ba887b7f97"
/>

Author: RobinMalfait

CHANGELOG.md

@@ -11,6 +11,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Show warning when using unsupported bare value data type in `--value(…)` ([#17464](https://github.com/tailwindlabs/tailwindcss/pull/17464))
 - PostCSS: Resolve an issue where changes to the input CSS file showed outdated content when using Turbopack ([#17554](https://github.com/tailwindlabs/tailwindcss/pull/17554))
+- Handle Ruby `%w` syntax in Slim pre processing ([#17557](https://github.com/tailwindlabs/tailwindcss/pull/17557))
 
 ## [4.1.2] - 2025-04-03
 

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

@@ -56,6 +56,28 @@ impl PreProcessor for Slim {
                     }
                 }
 
+                // Handle Ruby syntax with `%w[]` arrays embedded in Slim directly.
+                //
+                // E.g.:
+                //
+                // ```
+                // div [
+                //   class=%w[bg-blue-500 w-10 h-10]
+                // ]
+                // ```
+                b'%' if matches!(cursor.next, b'w' | b'W')
+                    && matches!(cursor.input.get(cursor.pos + 2), Some(b'[' | b'(' | b'{')) =>
+                {
+                    result[cursor.pos] = b' '; // Replace `%`
+                    cursor.advance();
+                    result[cursor.pos] = b' '; // Replace `w`
+                    cursor.advance();
+                    result[cursor.pos] = b' '; // Replace `[` or `(` or `{`
+                    bracket_stack.push(cursor.curr);
+                    cursor.advance(); // Move past the bracket
+                    continue;
+                }
+
                 // Any `[` preceded by an alphanumeric value will not be part of a candidate.
                 //
                 // E.g.:
@@ -281,4 +303,29 @@ mod tests {
         "#;
         Slim::test_extract_contains(input, vec!["flex", "items-center"]);
     }
+
+    // https://github.com/tailwindlabs/tailwindcss/issues/17542
+    #[test]
+    fn test_embedded_ruby_percent_w_extraction() {
+        let input = r#"
+            div[
+              class=%w[bg-blue-500 w-10 h-10]
+            ]
+            div[
+              class=%w[w-10 bg-green-500 h-10]
+            ]
+        "#;
+
+        let expected = r#"
+            div 
+              class=   bg-blue-500 w-10 h-10]
+            ]
+            div 
+              class=   w-10 bg-green-500 h-10]
+            ]
+        "#;
+
+        Slim::test(input, expected);
+        Slim::test_extract_contains(input, vec!["bg-blue-500", "bg-green-500", "w-10", "h-10"]);
+    }
 }