Take Items snapshot if any item is a __TransparentProxy

Even if we are in the default AppDomain it can happen that TaskParameterEventArgs is created in the default AppDomain, but the Items passed to it originate from a different AppDomain.

We have to detect this case and take the items snapshot immediately otherwise that AppDomain can get unloaded.

Author: KirillOsenkov

src/Build/BackEnd/Components/RequestBuilder/IntrinsicTasks/ItemGroupLoggingHelper.cs

@@ -5,6 +5,7 @@
 using System.Collections;
 using System.Collections.Generic;
 using System.Globalization;
+using System.Runtime.Remoting;
 using Microsoft.Build.BackEnd.Logging;
 using Microsoft.Build.Collections;
 using Microsoft.Build.Framework;
@@ -288,11 +289,39 @@ internal static TaskParameterEventArgs CreateTaskParameterEventArgs(
 
         private static void CreateItemsSnapshot(ref IList items)
         {
-            if (items == null || AppDomain.CurrentDomain.IsDefaultAppDomain())
+            if (items == null)
             {
                 return;
             }
 
+#if FEATURE_APPDOMAIN
+            // If we're in the default AppDomain, but any of the items come from a different AppDomain
+            // we need to take a snapshot of the items right now otherwise that AppDomain might get
+            // unloaded by the time we want to consume the items.
+            // If we're not in the default AppDomain, always take the items snapshot.
+            //
+            // It is unfortunate to need to be doing this check, but ResolveComReference and other tasks
+            // still use AppDomains and create a TaskParameterEventArgs in the default AppDomain, but
+            // pass it Items from another AppDomain.
+            if (AppDomain.CurrentDomain.IsDefaultAppDomain())
+            {
+                bool needsSnapshot = false;
+                foreach (var item in items)
+                {
+                    if (RemotingServices.IsTransparentProxy(item))
+                    {
+                        needsSnapshot = true;
+                        break;
+                    }
+                }
+
+                if (!needsSnapshot)
+                {
+                    return;
+                }
+            }
+#endif
+
             int count = items.Count;
             var cloned = new object[count];