Misc fixes for /question build

eng/BootStrapMSBuild.targets

@@ -68,6 +68,9 @@
     <ItemGroup>
       <InstalledVersionedExtensions Include="$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\**\*.targets" />
       <InstalledVersionedExtensions Include="$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\**\*.props" />
+      <InstalledVersionedExtensions Include="$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\**\Tracker*.dll" />
+      <InstalledVersionedExtensions Include="$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\**\Tracker*.exe" />
+      <InstalledVersionedExtensions Include="$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\**\FileTracker*.dll" />
       <SdkResolverFiles Include="$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Bin\SdkResolvers\Microsoft.DotNet.MSBuildSdkResolver\**\*.*" />
       <NuGetSdkResolverManifest Include= "$(RepoRoot)src\MSBuild\SdkResolvers\VS\Microsoft.Build.NuGetSdkResolver.xml" Condition="'$(MonoBuild)' != 'true'" />
       <NuGetSdkResolverManifest Include= "$(RepoRoot)src\MSBuild\SdkResolvers\Standalone\Microsoft.Build.NuGetSdkResolver.xml" Condition="'$(MonoBuild)' == 'true'" />

src/MSBuild/MSBuild.csproj

@@ -244,7 +244,7 @@
 
   <!-- Xsds are not TF or arch-specific so copy once them in the outer build -->
   <Target Name="CopyXsds" BeforeTargets="Build" Condition="'$(IsInnerBuild)' != 'true'">
-    <Copy SourceFiles="@(XsdsForVS)" DestinationFiles="@(XsdsForVS-&gt;'$([MSBuild]::NormalizeDirectory('$(ArtifactsDir)', 'xsd'))%(RecursiveDir)%(Filename)%(Extension)')" SkipUnchangedFiles="$(SkipCopyUnchangedFiles)" />
+    <Copy SourceFiles="@(XsdsForVS)" DestinationFiles="@(XsdsForVS-&gt;'$([MSBuild]::NormalizeDirectory('$(ArtifactsDir)', 'xsd'))%(RecursiveDir)%(Filename)%(Extension)')" SkipUnchangedFiles="true" />
   </Target>
 
   <!-- Include MSBuild.deps.json and MSBuild.runtimeconfig.json in ContentWithTargetPath so they will be copied to the output folder of projects

src/Samples/PortableTask/PortableTask.csproj

@@ -18,6 +18,6 @@
 
   <!-- This is only needed for a test in the MSBuild repo; it is unrelated to the PortableTask sample itself. -->
   <Target Name="CopyMSBuildUtilitiesToNewFolder" BeforeTargets="CopyFilesToOutputDirectory">
-    <Copy SourceFiles="$(PkgMicrosoft_Build_Utilities_Core)\lib\net46\Microsoft.Build.Utilities.Core.dll" DestinationFiles="$(OutDir)\OldMSBuild\Microsoft.Build.Utilities.Core.dll" />
+    <Copy SourceFiles="$(PkgMicrosoft_Build_Utilities_Core)\lib\net46\Microsoft.Build.Utilities.Core.dll" DestinationFiles="$(OutDir)\OldMSBuild\Microsoft.Build.Utilities.Core.dll" SkipUnchangedFiles="true"/>
   </Target>
 </Project>

src/Tasks.UnitTests/WriteLinesToFile_Tests.cs

@@ -238,6 +238,57 @@ public void QuestionWriteLinesWriteOnlyWhenDifferentTest()
             }
         }
 
+        /// <summary>
+        /// Question WriteLines to return true when Lines are empty.
+        /// </summary>
+        [Fact]
+        public void QuestionWriteLinesWhenLinesAreEmpty()
+        {
+            // Test the combination of:
+            // 1) File exists
+            // 2) Overwrite
+            // 3) WriteOnlyWhenDifferent
+
+            var fileExists = FileUtilities.GetTemporaryFile();
+            var fileNotExists = FileUtilities.GetTemporaryFileName();
+            try
+            {
+                TestWriteLines(fileExists, fileNotExists, Overwrite: true, WriteOnlyWhenDifferent: true);
+                TestWriteLines(fileExists, fileNotExists, Overwrite: false, WriteOnlyWhenDifferent: true);
+                TestWriteLines(fileExists, fileNotExists, Overwrite: true, WriteOnlyWhenDifferent: false);
+                TestWriteLines(fileExists, fileNotExists, Overwrite: false, WriteOnlyWhenDifferent: false);
+            }
+            finally
+            {
+                File.Delete(fileExists);
+            }
+
+            void TestWriteLines(string fileExists, string fileNotExists, bool Overwrite, bool WriteOnlyWhenDifferent)
+            {
+                var test1 = new WriteLinesToFile
+                {
+                    Overwrite = Overwrite,
+                    BuildEngine = new MockEngine(_output),
+                    File = new TaskItem(fileExists),
+                    WriteOnlyWhenDifferent = WriteOnlyWhenDifferent,
+                    FailIfNotIncremental = true,
+                    // Tests Lines = null.
+                };
+                test1.Execute().ShouldBeTrue();
+
+                var test2 = new WriteLinesToFile
+                {
+                    Overwrite = Overwrite,
+                    BuildEngine = new MockEngine(_output),
+                    File = new TaskItem(fileNotExists),
+                    WriteOnlyWhenDifferent = WriteOnlyWhenDifferent,
+                    FailIfNotIncremental = true,
+                    Lines = Array.Empty<ITaskItem>(),  // Test empty.
+                };
+                test2.Execute().ShouldBeTrue();
+            }
+        }
+
         /// <summary>
         /// Should create directory structure when target <see cref="WriteLinesToFile.File"/> does not exist.
         /// </summary>

src/Tasks/FileIO/WriteLinesToFile.cs

@@ -133,8 +133,11 @@ public override bool Execute()
 
                         if (FailIfNotIncremental)
                         {
-                            Log.LogErrorWithCodeFromResources("WriteLinesToFile.ErrorReadingFile", File.ItemSpec);
-                            return false;
+                            if (Lines?.Length > 0)
+                            {
+                                Log.LogErrorWithCodeFromResources("WriteLinesToFile.ErrorReadingFile", File.ItemSpec);
+                                return false;
+                            }
                         }
                         else
                         {
@@ -143,7 +146,7 @@ public override bool Execute()
                     }
                     else
                     {
-                        if (FailIfNotIncremental)
+                        if (FailIfNotIncremental && Lines?.Length > 0)
                         {
                             Log.LogErrorWithCodeFromResources("WriteLinesToFile.ErrorOrWarning", File.ItemSpec, string.Empty);
                             return false;