From 588c2154a5984bfa951f496d0386a34218a16cf9 Mon Sep 17 00:00:00 2001
From: FranklinDM <mrmineshafter17@gmail.com>
Date: Sat, 4 Mar 2023 00:53:46 +0800
Subject: [PATCH] Issue #2135 - Bug 1410578: Make <link rel="stylesheet"> work
 in shadow trees

---
 dom/base/nsStyleLinkElement.cpp               | 24 +++++++------------
 dom/html/HTMLLinkElement.cpp                  | 17 ++++---------
 .../test_shadowroot_inert_element.html        | 17 +------------
 layout/style/Loader.cpp                       | 12 ++++++----
 4 files changed, 21 insertions(+), 49 deletions(-)

diff --git a/dom/base/nsStyleLinkElement.cpp b/dom/base/nsStyleLinkElement.cpp
index 21a4f694a6..7ea7fce40c 100644
--- a/dom/base/nsStyleLinkElement.cpp
+++ b/dom/base/nsStyleLinkElement.cpp
@@ -304,14 +304,6 @@ nsStyleLinkElement::DoUpdateStyleSheet(nsIDocument* aOldDocument,
     return NS_OK;
   }
 
-  // Check for a ShadowRoot because link elements are inert in a
-  // ShadowRoot.
-  ShadowRoot* containingShadow = thisContent->GetContainingShadow();
-  if (thisContent->IsHTMLElement(nsGkAtoms::link) &&
-      (aOldShadowRoot || containingShadow)) {
-    return NS_OK;
-  }
-
   // XXXheycam ServoStyleSheets do not support <style scoped>.
   Element* oldScopeElement = nullptr;
   if (mStyleSheet) {
@@ -346,15 +338,16 @@ nsStyleLinkElement::DoUpdateStyleSheet(nsIDocument* aOldDocument,
     }
   }
 
-  // When static documents are created, stylesheets are cloned manually.
-  if (mDontLoadStyle || !mUpdatesEnabled ||
-      thisContent->OwnerDoc()->IsStaticDocument()) {
+  nsCOMPtr<nsIDocument> doc = thisContent->IsInShadowTree() ?
+    thisContent->OwnerDoc() : thisContent->GetUncomposedDoc();
+
+  // Loader could be null during unlink, see bug 1425866.
+  if (!doc || !doc->CSSLoader() || !doc->CSSLoader()->GetEnabled()) {
     return NS_OK;
   }
 
-  nsCOMPtr<nsIDocument> doc = thisContent->IsInShadowTree() ?
-    thisContent->OwnerDoc() : thisContent->GetUncomposedDoc();
-  if (!doc || !doc->CSSLoader()->GetEnabled()) {
+  // When static documents are created, stylesheets are cloned manually.
+  if (mDontLoadStyle || !mUpdatesEnabled || doc->IsStaticDocument()) {
     return NS_OK;
   }
 
@@ -426,8 +419,7 @@ nsStyleLinkElement::DoUpdateStyleSheet(nsIDocument* aOldDocument,
     rv = doc->CSSLoader()->
       LoadInlineStyle(thisContent, text, mLineNumber, title, media,
                       scopeElement, aObserver, &doneLoading, &isAlternate, &isExplicitlyEnabled);
-  }
-  else {
+  } else {
     nsAutoString integrity;
     thisContent->GetAttr(kNameSpaceID_None, nsGkAtoms::integrity, integrity);
     if (!integrity.IsEmpty()) {
diff --git a/dom/html/HTMLLinkElement.cpp b/dom/html/HTMLLinkElement.cpp
index df0cc72a40..b8e859cc00 100644
--- a/dom/html/HTMLLinkElement.cpp
+++ b/dom/html/HTMLLinkElement.cpp
@@ -162,7 +162,8 @@ HTMLLinkElement::HasDeferredDNSPrefetchRequest()
 }
 
 nsresult
-HTMLLinkElement::BindToTree(nsIDocument* aDocument, nsIContent* aParent,
+HTMLLinkElement::BindToTree(nsIDocument* aDocument,
+                            nsIContent* aParent,
                             nsIContent* aBindingParent,
                             bool aCompileEventHandlers)
 {
@@ -173,12 +174,8 @@ HTMLLinkElement::BindToTree(nsIDocument* aDocument, nsIContent* aParent,
                                                  aCompileEventHandlers);
   NS_ENSURE_SUCCESS(rv, rv);
 
-  // Link must be inert in ShadowRoot.
-  if (aDocument && !GetContainingShadow()) {
-    aDocument->RegisterPendingLinkUpdate(this);
-  }
-
-  if (IsInComposedDoc()) {
+  if (nsIDocument* doc = GetComposedDoc()) {
+    doc->RegisterPendingLinkUpdate(this);
     TryDNSPrefetchPreconnectOrPrefetch();
   }
 
@@ -222,11 +219,7 @@ HTMLLinkElement::UnbindFromTree(bool aDeep, bool aNullParent)
   // If this is reinserted back into the document it will not be
   // from the parser.
   nsCOMPtr<nsIDocument> oldDoc = GetUncomposedDoc();
-
-  // Check for a ShadowRoot because link elements are inert in a
-  // ShadowRoot.
-  ShadowRoot* oldShadowRoot = GetBindingParent() ?
-    GetBindingParent()->GetShadowRoot() : nullptr;
+  ShadowRoot* oldShadowRoot = GetContainingShadow();
 
   OwnerDoc()->UnregisterPendingLinkUpdate(this);
 
diff --git a/dom/tests/mochitest/webcomponents/test_shadowroot_inert_element.html b/dom/tests/mochitest/webcomponents/test_shadowroot_inert_element.html
index ca525adad5..04c27753a5 100644
--- a/dom/tests/mochitest/webcomponents/test_shadowroot_inert_element.html
+++ b/dom/tests/mochitest/webcomponents/test_shadowroot_inert_element.html
@@ -22,22 +22,7 @@ isnot(document.baseURI, "http://www.example.org/", "Base element should be inert
 
 SimpleTest.waitForExplicitFinish();
 
-// Check that <link> is inert.
-var numStyleBeforeLoad = document.styleSheets.length;
-
-shadow.innerHTML = '<link id="shadowlink" rel="stylesheet" type="text/css" href="inert_style.css" /><span id="shadowspan"></span>';
-shadow.applyAuthorStyles = true;
-var shadowSpan = shadow.getElementById("shadowspan");
-var shadowStyle = shadow.getElementById("shadowlink");
-
-function runChecks() {
-  isnot(getComputedStyle(shadowSpan, null).getPropertyValue("padding-top"), "10px", "Link element should be inert.");
-  is(document.styleSheets.length, numStyleBeforeLoad, "Document style count should remain the same because the style should not be in the doucment.");
-  is(shadow.styleSheets.length, 0, "Inert link should not add style to ShadowRoot.");
-  // Remove link to make sure we don't get assertions.
-  shadow.removeChild(shadowStyle);
-  SimpleTest.finish();
-};
+SimpleTest.finish();
 
 </script>
 </body>
diff --git a/layout/style/Loader.cpp b/layout/style/Loader.cpp
index 155ecbeeef..3d1e4826d5 100644
--- a/layout/style/Loader.cpp
+++ b/layout/style/Loader.cpp
@@ -2024,9 +2024,7 @@ Loader::LoadInlineStyle(nsIContent* aElement,
   PrepareSheet(sheet, aTitle, aMedia, nullptr, aScopeElement, *aIsAlternate, *aIsExplicitlyEnabled);
 
   if (aElement->HasFlag(NODE_IS_IN_SHADOW_TREE)) {
-    ShadowRoot* containingShadow = aElement->GetContainingShadow();
-    MOZ_ASSERT(containingShadow);
-    containingShadow->InsertSheet(sheet, aElement);
+    aElement->GetContainingShadow()->InsertSheet(sheet, aElement);
   } else {
     rv = InsertSheetInDoc(sheet, aElement, mDocument);
     NS_ENSURE_SUCCESS(rv, rv);
@@ -2120,8 +2118,12 @@ Loader::LoadStyleLink(nsIContent* aElement,
 
   PrepareSheet(sheet, aTitle, aMedia, nullptr, nullptr, *aIsAlternate, *aIsExplicitlyEnabled);
 
-  rv = InsertSheetInDoc(sheet, aElement, mDocument);
-  NS_ENSURE_SUCCESS(rv, rv);
+  if (aElement->HasFlag(NODE_IS_IN_SHADOW_TREE)) {
+    aElement->GetContainingShadow()->InsertSheet(sheet, aElement);
+  } else {
+    rv = InsertSheetInDoc(sheet, aElement, mDocument);
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
 
   nsCOMPtr<nsIStyleSheetLinkingElement> owningElement(do_QueryInterface(aElement));