From b2c435a18969a9e9f9ddabe8ab3ba1f1b16c29fc Mon Sep 17 00:00:00 2001
From: Francis Dominic Fajardo <fofajardo@up.edu.ph>
Date: Thu, 26 Jun 2025 21:01:56 +0800
Subject: [PATCH] Issue #2765 - Part 2: Create a helper function for resolving
 the non-NAC style context of a given NAC

---
 layout/base/nsLayoutUtils.cpp | 25 +++++++++++++++++++++++++
 layout/base/nsLayoutUtils.h   |  9 +++++++++
 2 files changed, 34 insertions(+)

diff --git a/layout/base/nsLayoutUtils.cpp b/layout/base/nsLayoutUtils.cpp
index 87ad428ab8..06014e5c50 100644
--- a/layout/base/nsLayoutUtils.cpp
+++ b/layout/base/nsLayoutUtils.cpp
@@ -9337,3 +9337,28 @@ nsLayoutUtils::ComputeGeometryBox(nsIFrame* aFrame,
 
   return r;
 }
+
+/* static */ nsStyleContext*
+nsLayoutUtils::GetNonAnonymousStyleContext(nsIFrame* aFrame)
+{
+  nsIContent* node = aFrame->GetContent();
+  MOZ_ASSERT(node, "No content for the given frame?");
+  while (node && node->IsInNativeAnonymousSubtree()) {
+    node = node->GetParent();
+  }
+  MOZ_ASSERT(node, "Native anonymous element with no originating node?");
+  if (nsIFrame* primaryFrame = node->GetPrimaryFrame()) {
+    return primaryFrame->StyleContext();
+  }
+  // If the element doesn't have primary frame, get the computed style
+  // from the element directly.
+  nsPresContext* pc = aFrame->PresContext();
+  MOZ_ASSERT(node == pc->Document()->GetRootElement(),
+             "Root element is the only case for this fallback "
+             "path to be triggered");
+  RefPtr<nsStyleContext> styleContext =
+      pc->StyleSet()->ResolveStyleFor(node->AsElement(), nullptr);
+  // Dropping the strong reference is fine because the style should be
+  // held strongly by the element.
+  return styleContext.get();
+}
diff --git a/layout/base/nsLayoutUtils.h b/layout/base/nsLayoutUtils.h
index 6091fb45e4..ea9a026007 100644
--- a/layout/base/nsLayoutUtils.h
+++ b/layout/base/nsLayoutUtils.h
@@ -2878,6 +2878,15 @@ public:
     return ResolveToLength<true>(aGap, aPercentageBasis);
   }
 
+  /**
+   * Returns the style context associated with the nearest non-native-anonymous
+   * ancestor of the given frame.
+   *
+   * @param aFrame The frame associated with native anonymous content.
+   * @return The resolved style context of the nearest non-anonymous DOM ancestor.
+   */
+  static nsStyleContext* GetNonAnonymousStyleContext(nsIFrame* aFrame);
+
 private:
   static uint32_t sFontSizeInflationEmPerLine;
   static uint32_t sFontSizeInflationMinTwips;