[Windows] Skip running tasks with no inputs (#23458)

This is a very minor perf improvements that could help when building
remotely from Windows with slow connections (i.e., from Devbox).

It skips running some tasks that not always have inputs to avoid the
unnecessary network round tripping.

Fixes #19600

Author: emaf

msbuild/Xamarin.Localization.MSBuild/MSBStrings.resx

@@ -1621,4 +1621,12 @@
             {2} and {3}: the different LogicalName metadata
         </comment>
     </data>
+
+    <data name="M7159" xml:space="preserve">
+        <value>Skipping {0} - {1} is empty.</value>
+        <comment>
+            {0}: the name of the MSBuild task that's being skipped (Copy, GetFullPaths, FilterStaticFrameworks, etc.).
+            {1}: the name of the property that is empty (SourceFiles, Items, FrameworkToPublish, etc.).
+        </comment>
+    </data>
 </root>

msbuild/Xamarin.MacDev.Tasks/MsBuildTasks/Copy.cs

@@ -1,18 +1,22 @@
 extern alias Microsoft_Build_Tasks_Core;
 
-using System;
-using System.IO;
 using System.Linq;
 
 using Microsoft.Build.Framework;
 
+using Xamarin.Localization.MSBuild;
 using Xamarin.Messaging.Build.Client;
 
 namespace Microsoft.Build.Tasks {
 	public class Copy : Microsoft_Build_Tasks_Core::Microsoft.Build.Tasks.Copy {
 		public string SessionId { get; set; } = string.Empty;
 		public override bool Execute ()
 		{
+			if (SourceFiles?.Any () != true) {
+				Log.LogMessage (MessageImportance.Low, MSBStrings.M7159 /* Skipping {0} - {1} is empty. */, nameof (Copy), nameof (SourceFiles));
+				return true;
+			}
+
 			if (!this.ShouldExecuteRemotely (SessionId))
 				return base.Execute ();
 

msbuild/Xamarin.MacDev.Tasks/Tasks/FilterStaticFrameworks.cs

@@ -22,6 +22,11 @@ public class FilterStaticFrameworks : XamarinTask, ITaskCallback {
 
 		public override bool Execute ()
 		{
+			if (FrameworkToPublish?.Any () != true) {
+				Log.LogMessage (MessageImportance.Low, MSBStrings.M7159 /* Skipping {0} - {1} is empty. */, nameof (FilterStaticFrameworks), nameof (FrameworkToPublish));
+				return true;
+			}
+
 			if (ShouldExecuteRemotely ())
 				return new TaskRunner (SessionId, BuildEngine4).RunAsync (this).Result;
 

msbuild/Xamarin.MacDev.Tasks/Tasks/GetFileSystemEntries.cs

@@ -43,6 +43,11 @@ public class GetFileSystemEntries : XamarinTask, ICancelableTask, ITaskCallback
 
 		public override bool Execute ()
 		{
+			if (DirectoryPath?.Any () != true) {
+				Log.LogMessage (MessageImportance.Low, MSBStrings.M7159 /* Skipping {0} - {1} is empty. */, nameof (GetFileSystemEntries), nameof (DirectoryPath));
+				return true;
+			}
+
 			if (ShouldExecuteRemotely ())
 				return new TaskRunner (SessionId, BuildEngine4).RunAsync (this).Result;
 

msbuild/Xamarin.MacDev.Tasks/Tasks/GetFullPaths.cs

@@ -6,7 +6,7 @@
 using Microsoft.Build.Framework;
 using Microsoft.Build.Utilities;
 
-using Xamarin.MacDev.Tasks;
+using Xamarin.Localization.MSBuild;
 using Xamarin.Messaging.Build.Client;
 
 #nullable enable
@@ -23,6 +23,11 @@ public class GetFullPaths : XamarinTask, ICancelableTask, ITaskCallback {
 
 		public override bool Execute ()
 		{
+			if (Items?.Any () != true) {
+				Log.LogMessage (MessageImportance.Low, MSBStrings.M7159 /* Skipping {0} - {1} is empty. */, nameof (GetFullPaths), nameof (Items));
+				return true;
+			}
+
 			if (ShouldExecuteRemotely ())
 				return new TaskRunner (SessionId, BuildEngine4).RunAsync (this).Result;