Bug 1343879 - Be consistent about the parent style context the document-level anonymous content container should get: it should get no parent style context.

Tag #1375

1 files changed, 15 insertions, 9 deletions

diff --git a/layout/base/nsCSSFrameConstructor.cpp b/layout/base/nsCSSFrameConstructor.cpp
index e88b2d62c..374764203 100644
--- a/layout/base/nsCSSFrameConstructor.cpp
+++ b/layout/base/nsCSSFrameConstructor.cpp
@@ -10751,16 +10751,22 @@ nsCSSFrameConstructor::AddFCItemsForAnonymousContent(
       }
     }
 
-    if (inheritFrame->GetType() == nsGkAtoms::canvasFrame) {
-      // CorrectStyleParentFrame returns nullptr if the prospective parent is
-      // the canvas frame, so avoid calling it in that situation.
-    } else {
-      inheritFrame = nsFrame::CorrectStyleParentFrame(inheritFrame, pseudo);
-    }
-    Element* originating = pseudo ? inheritFrame->GetContent()->AsElement() : nullptr;
-
+    nsIFrame* styleParentFrame =
+      nsFrame::CorrectStyleParentFrame(inheritFrame, pseudo);
+    // The only way we can not have a style parent now is if inheritFrame is the
+    // canvas frame and we're the NAC parent for all the things added via
+    // nsIDocument::InsertAnonymousContent.
+    MOZ_ASSERT_IF(!styleParentFrame,
+                  inheritFrame->GetType() == nsGkAtoms::canvasFrame);
+    // And that anonymous div has no pseudo.
+    MOZ_ASSERT_IF(!styleParentFrame, !pseudo);
+
+    Element* originating =
+      pseudo ? styleParentFrame->GetContent()->AsElement() : nullptr;
+    nsStyleContext* parentStyle =
+      styleParentFrame ? styleParentFrame->StyleContext() : nullptr;
     styleContext =
-      ResolveStyleContext(inheritFrame->StyleContext(), content, &aState, originating);
+      ResolveStyleContext(parentStyle, content, &aState, originating);
 
     nsTArray<nsIAnonymousContentCreator::ContentInfo>* anonChildren = nullptr;
     if (!aAnonymousItems[i].mChildren.IsEmpty()) {