Add output parameter to Copy task and condition Touch task based off of it.

Author: benvillalobos

ref/Microsoft.Build.Tasks.Core/net/Microsoft.Build.Tasks.Core.cs

@@ -194,6 +194,8 @@ public partial class Copy : Microsoft.Build.Tasks.TaskExtension, Microsoft.Build
     {
         public Copy() { }
         [Microsoft.Build.Framework.OutputAttribute]
+        public bool CopiedAtLeastOneFile { get { throw null; } }
+        [Microsoft.Build.Framework.OutputAttribute]
         public Microsoft.Build.Framework.ITaskItem[] CopiedFiles { get { throw null; } }
         [Microsoft.Build.Framework.OutputAttribute]
         public Microsoft.Build.Framework.ITaskItem[] DestinationFiles { get { throw null; } set { } }

ref/Microsoft.Build.Tasks.Core/netstandard/Microsoft.Build.Tasks.Core.cs

@@ -124,6 +124,8 @@ public partial class Copy : Microsoft.Build.Tasks.TaskExtension, Microsoft.Build
     {
         public Copy() { }
         [Microsoft.Build.Framework.OutputAttribute]
+        public bool CopiedAtLeastOneFile { get { throw null; } }
+        [Microsoft.Build.Framework.OutputAttribute]
         public Microsoft.Build.Framework.ITaskItem[] CopiedFiles { get { throw null; } }
         [Microsoft.Build.Framework.OutputAttribute]
         public Microsoft.Build.Framework.ITaskItem[] DestinationFiles { get { throw null; } set { } }

src/Tasks/Copy.cs

@@ -139,6 +139,9 @@ public Copy()
         [Output]
         public ITaskItem[] CopiedFiles { get; private set; }
 
+        [Output]
+        public bool CopiedAtLeastOneFile { get; private set; }
+
         /// <summary>
         /// Whether to overwrite files in the destination
         /// that have the read-only attribute set.
@@ -297,6 +300,7 @@ FileState destinationFileState  // The destination file
                 Log.LogMessage(MessageImportance.Normal, FileComment, sourceFilePath, destinationFilePath);
 
                 File.Copy(sourceFileState.Name, destinationFileState.Name, true);
+                CopiedAtLeastOneFile = true;
             }
 
             destinationFileState.Reset();

src/Tasks/Microsoft.Common.CurrentVersion.targets

@@ -4696,6 +4696,7 @@ Copyright (C) Microsoft Corporation. All rights reserved.
 
       <Output TaskParameter="DestinationFiles" ItemName="FileWritesShareable"/>
       <Output TaskParameter="CopiedFiles" ItemName="ReferencesCopiedInThisBuild"/>
+      <Output TaskParameter="CopiedAtLeastOneFile" PropertyName="CopiedAtLeastOneFile"/>
 
     </Copy>
 
@@ -4705,7 +4706,7 @@ Copyright (C) Microsoft Corporation. All rights reserved.
          input to projects that reference this one. -->
     <Touch Files="@(CopyUpToDateMarker)"
            AlwaysCreate="true"
-           Condition="'@(ReferencesCopiedInThisBuild)' != ''">
+           Condition="'@(ReferencesCopiedInThisBuild)' != '' and '$(CopiedAtLeastOneFile)' == 'true'">
         <Output TaskParameter="TouchedFiles" ItemName="FileWrites" />
     </Touch>