From c7992b86566115928a7434700f4028f92d7788a7 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Emilio=20Cobos=20=C3=81lvarez?= <emilio@crisal.io>
Date: Fri, 17 Apr 2020 22:55:03 +0000
Subject: [PATCH] Bug 1449522 - Cleanup some parent walks in StyleSheet code.
 r=nordzilla

Differential Revision: https://phabricator.services.mozilla.com/D71410
---
 layout/style/StyleSheet.cpp | 47 +++++++++++++++++--------------------
 layout/style/StyleSheet.h   | 19 ++++++++++-----
 2 files changed, 35 insertions(+), 31 deletions(-)

diff --git a/layout/style/StyleSheet.cpp b/layout/style/StyleSheet.cpp
index 5d0c3063d3df..491d1db57c1c 100644
--- a/layout/style/StyleSheet.cpp
+++ b/layout/style/StyleSheet.cpp
@@ -159,28 +159,26 @@ Document* StyleSheet::GetAssociatedDocument() const {
 
 dom::DocumentOrShadowRoot* StyleSheet::GetAssociatedDocumentOrShadowRoot()
     const {
-  for (const auto* sheet = this; sheet; sheet = sheet->mParentSheet) {
-    if (sheet->mDocumentOrShadowRoot) {
-      return sheet->mDocumentOrShadowRoot;
-    }
-    if (sheet->IsConstructed()) {
-      return sheet->mConstructorDocument;
-    }
+  const StyleSheet& outer = OutermostSheet();
+  if (outer.mDocumentOrShadowRoot) {
+    return outer.mDocumentOrShadowRoot;
+  }
+  if (outer.IsConstructed()) {
+    return outer.mConstructorDocument;
   }
   return nullptr;
 }
 
 Document* StyleSheet::GetKeptAliveByDocument() const {
-  for (const auto* sheet = this; sheet; sheet = sheet->mParentSheet) {
-    if (sheet->mDocumentOrShadowRoot) {
-      return sheet->mDocumentOrShadowRoot->AsNode().GetComposedDoc();
-    }
-    if (sheet->IsConstructed()) {
-      for (DocumentOrShadowRoot* adopter : sheet->mAdopters) {
-        MOZ_ASSERT(adopter->AsNode().OwnerDoc() == sheet->mConstructorDocument);
-        if (adopter->AsNode().IsInComposedDoc()) {
-          return sheet->mConstructorDocument.get();
-        }
+  const StyleSheet& outer = OutermostSheet();
+  if (outer.mDocumentOrShadowRoot) {
+    return outer.mDocumentOrShadowRoot->AsNode().GetComposedDoc();
+  }
+  if (outer.IsConstructed()) {
+    for (DocumentOrShadowRoot* adopter : outer.mAdopters) {
+      MOZ_ASSERT(adopter->AsNode().OwnerDoc() == outer.mConstructorDocument);
+      if (adopter->AsNode().IsInComposedDoc()) {
+        return outer.mConstructorDocument.get();
       }
     }
   }
@@ -306,15 +304,14 @@ void StyleSheet::ApplicableStateChanged(bool aApplicable) {
     }
   };
 
-  for (const auto* sheet = this; sheet; sheet = sheet->mParentSheet) {
-    if (sheet->mDocumentOrShadowRoot) {
-      Notify(*sheet->mDocumentOrShadowRoot);
-    }
+  const StyleSheet& sheet = OutermostSheet();
+  if (sheet.mDocumentOrShadowRoot) {
+    Notify(*sheet.mDocumentOrShadowRoot);
+  }
 
-    for (DocumentOrShadowRoot* adopter : sheet->mAdopters) {
-      MOZ_ASSERT(adopter, "adopters should never be null");
-      Notify(*adopter);
-    }
+  for (DocumentOrShadowRoot* adopter : sheet.mAdopters) {
+    MOZ_ASSERT(adopter, "adopters should never be null");
+    Notify(*adopter);
   }
 }
 
diff --git a/layout/style/StyleSheet.h b/layout/style/StyleSheet.h
index e5ab7a1491d9..7dd52f51e7a1 100644
--- a/layout/style/StyleSheet.h
+++ b/layout/style/StyleSheet.h
@@ -394,12 +394,7 @@ class StyleSheet final : public nsICSSLoaderObserver, public nsWrapperCache {
   // True if any of this sheet's ancestors were created through the
   // Constructable StyleSheets API
   bool SelfOrAncestorIsConstructed() const {
-    for (auto* sheet = this; sheet; sheet = sheet->mParentSheet) {
-      if (sheet->IsConstructed()) {
-        return true;
-      }
-    }
-    return false;
+    return OutermostSheet().IsConstructed();
   }
 
   // Ture if the sheet's constructor document matches the given document
@@ -473,6 +468,18 @@ class StyleSheet final : public nsICSSLoaderObserver, public nsWrapperCache {
     mState |= State::ModifiedRules | State::ModifiedRulesForDevtools;
   }
 
+  const StyleSheet& OutermostSheet() const {
+    auto* current = this;
+    while (current->mParentSheet) {
+      MOZ_ASSERT(!current->mDocumentOrShadowRoot,
+                 "Shouldn't be set on child sheets");
+      MOZ_ASSERT(!current->mConstructorDocument,
+                 "Shouldn't be set on child sheets");
+      current = current->mParentSheet;
+    }
+    return *current;
+  }
+
   StyleSheetInfo& Inner() {
     MOZ_ASSERT(mInner);
     return *mInner;