Merge commit '2dc2247d6616f895c11328357d64625c678739a8'

Author: Mirroring

src/System.Windows.Forms/src/System/Windows/Forms/ToolStripItemCollection.cs

@@ -141,16 +141,23 @@ public void AddRange(ToolStripItemCollection toolStripItems)
             throw new NotSupportedException(SR.ToolStripItemCollectionIsReadOnly);
         }
 
+        // Return early if the collection is empty.
+        if (toolStripItems.Count == 0)
+        {
+            return;
+        }
+
         // ToolStripDropDown will look for PropertyNames.Items to determine if it needs
         // to resize itself.
         using (new LayoutTransaction(_owner, _owner!, PropertyNames.Items))
         {
-            for (int i = 0; i < toolStripItems.Count; i++)
+            // Create a temporary array to avoid modifying the original collection during iteration.
+            // Items will be removed from toolStripsItems collection when they are added to this collection
+            // if they had a different owner control.
+            var itemsToAdd = toolStripItems.InnerList.ToArray();
+            foreach (ToolStripItem item in itemsToAdd)
             {
-                // Items are removed from their origin when added to a different owner.
-                // Decrement the index to always add the items from index 0 which will preserve
-                // the original order and avoid a pesky ArgumentOutOfRangeException.
-                Add(toolStripItems[i--]);
+                Add(item);
             }
         }
     }

src/System.Windows.Forms/tests/UnitTests/System/Windows/Forms/ToolStripItemCollectionTests.cs

@@ -113,11 +113,36 @@ public void ToolStripItemCollection_AddRange_ToolStripItemCollection_Success()
         toolStripDropDownButton.DropDownItems.Add("b");
         toolStripDropDownButton.DropDownItems.Add("c");
         contextMenuStrip.Items.AddRange(toolStripDropDownButton.DropDownItems);
+
+        Assert.Empty(toolStripDropDownButton.DropDownItems);
         Assert.Equal(3, contextMenuStrip.Items.Count);
 
         // Validate order.
         Assert.Equal("a", contextMenuStrip.Items[0].Text);
         Assert.Equal("b", contextMenuStrip.Items[1].Text);
         Assert.Equal("c", contextMenuStrip.Items[2].Text);
     }
+
+    [WinFormsFact]
+    public void ToolStripItemCollection_AddRange_ToolStripItemCollection_SameOwner_Success()
+    {
+        using ToolStrip toolStrip = new();
+
+        // Create a ToolStripItemCollection with 2 items
+        ToolStripItemCollection itemCollection = new(toolStrip,
+            [
+                new ToolStripButton("Button 1"),
+                new ToolStripButton("Button 2")
+            ]);
+
+        Assert.Equal(0, toolStrip.Items.Count);
+
+        toolStrip.Items.AddRange(itemCollection);
+
+        Assert.Equal(2, itemCollection.Count);
+        Assert.Equal(2, toolStrip.Items.Count);
+
+        Assert.Equal("Button 1", toolStrip.Items[0].Text);
+        Assert.Equal("Button 2", toolStrip.Items[1].Text);
+    }
 }