Ensure extracting candidates from JS embedded in a PHP string works as expected (#17031)

This PR fixes an issue where candidates are not properly extractor when
they end in `\`. This can happen if you embed a programming language
like JS inside another language like PHP where you need to escape some
strings.

Here is an example of Livewire flux:
```blade
@php
if ($sidebarIsStashable) {
    $attributes = $attributes->merge([
        'x-init' => '$el.classList.add(\'-translate-x-full\'); $el.classList.add(\'transition-transform\')',
        //                                                ^                                            ^
    ]);
}
@endphp

<div x-data {{ $attributes->class('border-r w-64 p-4 min-h-dvh max-h-dvh top-0 fixed left-0') }}>
    {{ $slot }}
</div>
```
Where the `\'` is causing some issues.

Another solution might be to add a custom pre processor for blade files
where we drop the escaped characters, but that felt overkill for now
because some escapes are still valid.

Fixes: #17023

# Test plan

1. Added a test to cover this case.
2. Existing tests still pass

Author: RobinMalfait

CHANGELOG.md

@@ -25,6 +25,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Ensure strings in Pug and Slim templates are handled correctly ([#17000](https://github.com/tailwindlabs/tailwindcss/pull/17000))
 - Ensure `}` and `{` are valid boundary characters when extracting candidates ([#17001](https://github.com/tailwindlabs/tailwindcss/pull/17001))
 - Add `razor`/`cshtml` pre processing ([#17027](https://github.com/tailwindlabs/tailwindcss/pull/17027))
+- Ensure extracting candidates from JS embedded in a PHP string works as expected ([#17031](https://github.com/tailwindlabs/tailwindcss/pull/17031))
 
 ## [4.0.11] - 2025-03-06
 

crates/oxide/src/extractor/boundary.rs

@@ -97,6 +97,18 @@ enum Class {
     //                ^
     // ```
     #[bytes(b'=')]
+    // Escaped character when embedding one language in another via strings, e.g.:
+    //
+    // ```
+    // $attributes->merge([
+    //   'x-init' => '$el.classList.add(\'-translate-x-full\'); $el.classList.add(\'transition-transform\')',
+    //                                                     ^                                            ^
+    // ]);
+    // ```
+    //
+    // In this case there is some JavaScript embedded in an string in PHP and some of the quotes
+    // need to be escaped.
+    #[bytes(b'\\')]
     After,
 
     #[fallback]

crates/oxide/src/extractor/mod.rs

@@ -888,6 +888,39 @@ mod tests {
         );
     }
 
+    #[test]
+    fn test_js_embedded_in_php_syntax() {
+        // Escaped single quotes
+        let input = r#"
+            @php
+            if ($sidebarIsStashable) {
+                $attributes = $attributes->merge([
+                    'x-init' => '$el.classList.add(\'-translate-x-full\'); $el.classList.add(\'transition-transform\')',
+                ]);
+            }
+            @endphp
+        "#;
+        assert_extract_candidates_contains(
+            input,
+            vec!["-translate-x-full", "transition-transform"],
+        );
+
+        // Double quotes
+        let input = r#"
+            @php
+            if ($sidebarIsStashable) {
+                $attributes = $attributes->merge([
+                    'x-init' => "\$el.classList.add('-translate-x-full'); \$el.classList.add('transition-transform')",
+                ]);
+            }
+            @endphp
+        "#;
+        assert_extract_candidates_contains(
+            input,
+            vec!["-translate-x-full", "transition-transform"],
+        );
+    }
+
     // https://github.com/tailwindlabs/tailwindcss/issues/16978
     #[test]
     fn test_classes_containing_number_followed_by_dash_or_underscore() {