Fix: Add support for stylesheet MIME type quirk in quirks mode (#36338)

This PR implements the HTML spec quirk for stylesheets:
https://html.spec.whatwg.org/multipage/#link-type-stylesheet

The implementation adds a check in `stylesheet_loader.rs` to handle this
quirk condition correctly, and adds a new WPT test to verify that
same-origin non-CSS MIME type resources are properly treated as CSS in
quirks mode.

Testing: Added a new WPT test (`quirk-origin-check-positive.html`) that
verifies the positive case for this quirk.
Fixes: https://github.com/servo/servo/issues/36324

---------

Signed-off-by: saku-1101 <sakupi1101@outlook.jp>

4 files changed, 45 insertions, 1 deletions

diff --git a/components/script/stylesheet_loader.rs b/components/script/stylesheet_loader.rs
index 6290d2709cc..7c7f7f98a07 100644
--- a/components/script/stylesheet_loader.rs
+++ b/components/script/stylesheet_loader.rs
@@ -15,6 +15,7 @@ use net_traits::{
 };
 use servo_arc::Arc;
 use servo_url::ServoUrl;
+use style::context::QuirksMode;
 use style::media_queries::MediaList;
 use style::parser::ParserContext;
 use style::shared_lock::{Locked, SharedRwLock};
@@ -164,7 +165,16 @@ impl FetchResponseListener for StylesheetContext {
             let is_css = metadata.content_type.is_some_and(|ct| {
                 let mime: Mime = ct.into_inner().into();
                 mime.type_() == mime::TEXT && mime.subtype() == mime::CSS
-            });
+            }) || (
+                // Quirk: If the document has been set to quirks mode,
+                // has the same origin as the URL of the external resource,
+                // and the Content-Type metadata of the external resource
+                // is not a supported style sheet type, the user agent must
+                // instead assume it to be text/css.
+                // <https://html.spec.whatwg.org/multipage/#link-type-stylesheet>
+                document.quirks_mode() == QuirksMode::Quirks &&
+                    document.origin().immutable().clone() == metadata.final_url.origin()
+            );
 
             let data = if is_css {
                 let data = std::mem::take(&mut self.data);
diff --git a/tests/wpt/meta/MANIFEST.json b/tests/wpt/meta/MANIFEST.json
index a30e793a3d4..e50b0df3481 100644
--- a/tests/wpt/meta/MANIFEST.json
+++ b/tests/wpt/meta/MANIFEST.json
@@ -474568,6 +474568,14 @@
        "80fbe8db6cbfc1f6e478b6c3cc8d2ae3c707c053",
        []
       ]
+     },
+     "stylesheet": {
+      "resources": {
+       "quirk-stylesheet.css.txt": [
+        "d2ae382583192b0284aa44c038811e7254a9386b",
+        []
+       ]
+      }
      }
     },
     "meta": {
@@ -719907,6 +719915,13 @@
       }
      },
      "stylesheet": {
+      "quirk-origin-check-positive.html": [
+       "02ab832cbe207c9bbfb1d16cbdc9a685b474372c",
+       [
+        null,
+        {}
+       ]
+      ],
       "quirk-origin-check-recursive-import.html": [
        "c0053f1f29ad8f23dbebdd41b38dbdd8537e9e27",
        [
diff --git a/tests/wpt/tests/html/links/stylesheet/quirk-origin-check-positive.html b/tests/wpt/tests/html/links/stylesheet/quirk-origin-check-positive.html
new file mode 100644
index 00000000000..02ab832cbe2
--- /dev/null
+++ b/tests/wpt/tests/html/links/stylesheet/quirk-origin-check-positive.html
@@ -0,0 +1,18 @@
+<!-- quirks -->
+<title>Same-origin stylesheet with non-CSS MIME type quirk</title>
+<link rel="help" href="https://html.spec.whatwg.org/multipage/#link-type-stylesheet">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<link rel="stylesheet" href="resources/quirk-stylesheet.css.txt">
+<p class="test">This text should be green.</p>
+<script>
+setup({ single_test: true });
+onload = () => {
+  assert_equals(
+    getComputedStyle(document.querySelector('.test')).color,
+    'rgb(0, 128, 0)',
+    "Same-origin stylesheet with non-CSS MIME type should be applied in quirks mode"
+  );
+  done();
+};
+</script>
\ No newline at end of file
diff --git a/tests/wpt/tests/html/links/stylesheet/resources/quirk-stylesheet.css.txt b/tests/wpt/tests/html/links/stylesheet/resources/quirk-stylesheet.css.txt
new file mode 100644
index 00000000000..d2ae3825831
--- /dev/null
+++ b/tests/wpt/tests/html/links/stylesheet/resources/quirk-stylesheet.css.txt
@@ -0,0 +1 @@
+.test { color: green; }
\ No newline at end of file