From 9cd7fd3bf4d5369a6948ba48d628668320aa427d Mon Sep 17 00:00:00 2001
From: Moonchild <moonchild@palemoon.org>
Date: Sat, 14 Oct 2023 14:16:26 +0200
Subject: [PATCH] Issue #2340 - Return an array (actually frozen sequence) for
 {border|content}BoxSize

Resolves #2340
---
 dom/base/ResizeObserver.cpp      | 24 ++++++++++++++++++++++++
 dom/base/ResizeObserver.h        | 10 +++-------
 dom/webidl/ResizeObserver.webidl |  8 ++++++--
 3 files changed, 33 insertions(+), 9 deletions(-)

diff --git a/dom/base/ResizeObserver.cpp b/dom/base/ResizeObserver.cpp
index 51fd603217..ca25c06e43 100644
--- a/dom/base/ResizeObserver.cpp
+++ b/dom/base/ResizeObserver.cpp
@@ -303,6 +303,30 @@ ResizeObserverEntry::Constructor(const GlobalObject& aGlobal,
   return observerEntry.forget();
 }
 
+void ResizeObserverEntry::GetBorderBoxSize(
+    nsTArray<RefPtr<ResizeObserverSize>>& aRetVal) const {
+  // In the resize-observer-1 spec, there will only be a single
+  // ResizeObserverSize returned in the FrozenArray.
+  //
+  // Note: the usage of FrozenArray is to support elements that have multiple
+  // fragments, which occur in multi-column scenarios. See:
+  // https://drafts.csswg.org/resize-observer/#resize-observer-entry-interface
+  aRetVal.Clear();
+  aRetVal.AppendElement(mBorderBoxSize);
+}
+
+void ResizeObserverEntry::GetContentBoxSize(
+    nsTArray<RefPtr<ResizeObserverSize>>& aRetVal) const {
+  // In the resize-observer-1 spec, there will only be a single
+  // ResizeObserverSize returned in the FrozenArray.
+  //
+  // Note: the usage of FrozenArray is to support elements that have multiple
+  // fragments, which occur in multi-column scenarios.
+  // https://drafts.csswg.org/resize-observer/#resize-observer-entry-interface
+  aRetVal.Clear();
+  aRetVal.AppendElement(mContentBoxSize);
+}
+
 void
 ResizeObserverEntry::SetBorderBoxSize(const nsSize& aSize) {
   nsIFrame* frame = mTarget->GetPrimaryFrame();
diff --git a/dom/base/ResizeObserver.h b/dom/base/ResizeObserver.h
index 56675693ce..ca87a080b4 100644
--- a/dom/base/ResizeObserver.h
+++ b/dom/base/ResizeObserver.h
@@ -163,14 +163,10 @@ public:
 
   /**
    * Returns target's logical border-box size and content-box size as
-   * ResizeObserverSize.
+   * a ResizeObserverSize array.
    */
-  ResizeObserverSize* BorderBoxSize() const { 
-    return mBorderBoxSize;
-  }
-  ResizeObserverSize* ContentBoxSize() const { 
-    return mContentBoxSize;
-  }
+  void GetBorderBoxSize(nsTArray<RefPtr<ResizeObserverSize>>& aRetVal) const;
+  void GetContentBoxSize(nsTArray<RefPtr<ResizeObserverSize>>& aRetVal) const;
 
   // Set borderBoxSize.
   void SetBorderBoxSize(const nsSize& aSize);
diff --git a/dom/webidl/ResizeObserver.webidl b/dom/webidl/ResizeObserver.webidl
index d764af7cbd..e77fed294e 100644
--- a/dom/webidl/ResizeObserver.webidl
+++ b/dom/webidl/ResizeObserver.webidl
@@ -34,8 +34,12 @@ callback ResizeObserverCallback = void (sequence<ResizeObserverEntry> entries, R
 interface ResizeObserverEntry {
     readonly attribute Element target;
     readonly attribute DOMRectReadOnly? contentRect;
-    readonly attribute ResizeObserverSize borderBoxSize;
-    readonly attribute ResizeObserverSize contentBoxSize;
+    // We are using a [Pure, Cached, Frozen] sequence since `FrozenArray` is not implemented in webidl.
+    // This is functionally similar enough. As of #2340 Mozilla has not implemented this yet, either.
+    [Frozen, Cached, Pure]
+    readonly attribute sequence<ResizeObserverSize> borderBoxSize;
+    [Frozen, Cached, Pure]
+    readonly attribute sequence<ResizeObserverSize> contentBoxSize;
 };
 
 [Pref="layout.css.resizeobserver.enabled"]