The PresentationBuildTasks.dll built out of the .NET Core codebase is not being used for msbuild based builds (i.e., when $(MSBuildRuntimeType)==Full) of WPF projects that use WindowsDesktop SDK. Instead, the PresentationBuildTasks.dll from GAC, i.e., the DLL that shipped with .NET Framework, is being used for builds instead. (#2075)

This is because the *first* occurance of an `UsingTask` element that applies to a `TaskName` will always be used - it can not be overridden by subsequent `UsingTask` entries (this is unlike `Property` and `Item` behavior). See note in https://github.com/MicrosoftDocs/visualstudio-docs/blob/master/docs/msbuild/usingtask-element-msbuild.md immediate after the **Syntax** section (Note: The msbuild team added this note after identifying this behavior as part of investiaging this PresentationBuildTasks.dll issue).

The fix ensures that the `UsingTask` declarations supplied by the WindowsDesktop SDK precede those supplied by .NET Framework's copy of `Microsoft.WinFX.targets` by introducing a new `.props` file - `Microsoft.WinFX.props` - and moving a small number of `Property` and `UsingTask` declartions into it. Since `.props` are imported before `targets`, the `UsingTask` declarations supplied by WindowsDesktop SDK will thus take precedence.

Author: vatsan-madhavan

eng/WpfArcadeSdk/tools/Pbt.props

@@ -1,5 +1,6 @@
 <Project>
   <PropertyGroup>
+    <LocalMicrosoftWinFXProps>$(RepoRoot)src\Microsoft.DotNet.Wpf\src\PresentationBuildTasks\Microsoft.WinFX.props</LocalMicrosoftWinFXProps>
     <LocalMicrosoftWinFXTargets>$(RepoRoot)src\Microsoft.DotNet.Wpf\src\PresentationBuildTasks\Microsoft.WinFX.targets</LocalMicrosoftWinFXTargets>
   </PropertyGroup>
 
@@ -34,6 +35,8 @@
             Project="../targets/Microsoft.NET.Sdk.WindowsDesktop.props"
             Condition="!Exists('$(LocalMicrosoftWinFXTargets)') And '$(InternalMarkupCompilation)'=='true'"/>
             
+    We need Microsoft.WinFx.props though, so that's imported here specifically. 
+            
     The use of Microsoft.NET.Sdk.WindowsDesktop doesn't break the source-build promise. 
       - Microsoft.NET.Sdk.WindowsDesktop is built from sources
       - It is used for compilation of assemblies in dotnet-wpf-int (the internal WPF repo), and serves as a 
@@ -42,4 +45,18 @@
         fall back to use local PBT project outputs for their compilation (instead of using WindowsDesktop Sdk package
         as a convenient 'transport package'). 
   -->
+  
+  <!-- 
+    If local PresentationBuildTasks project is present, then import WinFX.props from local sources;
+    otherwise import Microsoft.NET.Sdk.WindowsDesktop.props from Microsoft.NET.Sdk.WindowsDesktop
+    
+    We can not really test for $(InternalMarkupCompilation)==true here. It is usually defined
+    in the csproj - which is included after props (but before targets). 
+  -->
+  <Import Project="$(WpfSourceDir)PresentationBuildTasks\Microsoft.WinFX.props"
+          Condition="Exists('$(LocalMicrosoftWinFXProps)') "/>
+  
+  <Import Sdk="Microsoft.NET.Sdk.WindowsDesktop"
+        Project="../targets/Microsoft.WinFx.props"
+        Condition="!Exists('$(LocalMicrosoftWinFXProps)')"/>
 </Project>

packaging/Microsoft.NET.Sdk.WindowsDesktop/targets/Microsoft.NET.Sdk.WindowsDesktop.props

@@ -204,4 +204,6 @@
 
     <SupportedTargetFramework Remove="@(_UnsupportedNETCoreAppTargetFramework);@(_UnsupportedNETStandardTargetFramework);@(_UnsupportedNETFrameworkTargetFramework)" />
   </ItemGroup>
+
+  <Import Project="Microsoft.WinFX.props" />
 </Project>

src/Microsoft.DotNet.Wpf/src/PresentationBuildTasks/Microsoft.WinFx.props

@@ -0,0 +1,16 @@
+<Project>
+  <PropertyGroup>
+    <_PresentationBuildTasksTfm Condition="'$(MSBuildRuntimeType)' == 'Core'">netcoreapp2.1</_PresentationBuildTasksTfm>
+    <_PresentationBuildTasksTfm Condition="'$(MSBuildRuntimeType)' != 'Core'">net472</_PresentationBuildTasksTfm>
+    <_PresentationBuildTasksAssembly Condition="'$(_PresentationBuildTasksAssembly)'==''">$([System.IO.Path]::GetFullPath('$(MSBuildThisFileDirectory)..\tools\$(_PresentationBuildTasksTfm)\PresentationBuildTasks.dll'))</_PresentationBuildTasksAssembly>
+  </PropertyGroup>
+
+  <UsingTask TaskName="Microsoft.Build.Tasks.Windows.MarkupCompilePass1" AssemblyFile="$(_PresentationBuildTasksAssembly)" />
+  <UsingTask TaskName="Microsoft.Build.Tasks.Windows.UidManager" AssemblyFile="$(_PresentationBuildTasksAssembly)" />
+  <UsingTask TaskName="Microsoft.Build.Tasks.Windows.ResourcesGenerator" AssemblyFile="$(_PresentationBuildTasksAssembly)" />
+  <UsingTask TaskName="Microsoft.Build.Tasks.Windows.FileClassifier" AssemblyFile="$(_PresentationBuildTasksAssembly)" />
+  <UsingTask TaskName="Microsoft.Build.Tasks.Windows.MarkupCompilePass2" AssemblyFile="$(_PresentationBuildTasksAssembly)" />
+  <UsingTask TaskName="Microsoft.Build.Tasks.Windows.GenerateTemporaryTargetAssembly" AssemblyFile="$(_PresentationBuildTasksAssembly)" />
+  <UsingTask TaskName="Microsoft.Build.Tasks.Windows.MergeLocalizationDirectives" AssemblyFile="$(_PresentationBuildTasksAssembly)" />
+  
+</Project>

src/Microsoft.DotNet.Wpf/src/PresentationBuildTasks/Microsoft.WinFx.targets

@@ -1,28 +1,10 @@
 <Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
-
   <PropertyGroup>
-
-    <_PresentationBuildTasksTfm Condition="'$(MSBuildRuntimeType)' == 'Core'">netcoreapp2.1</_PresentationBuildTasksTfm>
-    <_PresentationBuildTasksTfm Condition="'$(MSBuildRuntimeType)' != 'Core'">net472</_PresentationBuildTasksTfm>
-    <_PresentationBuildTasksAssembly Condition="'$(_PresentationBuildTasksAssembly)'==''">$(MSBuildThisFileDirectory)..\tools\$(_PresentationBuildTasksTfm)\PresentationBuildTasks.dll</_PresentationBuildTasksAssembly>
-
     <AlwaysCompileMarkupFilesInSeparateDomain Condition="'$(BuildingInsideVisualStudio)' == 'true' and '$(AlwaysCompileMarkupFilesInSeparateDomain)' == ''">true</AlwaysCompileMarkupFilesInSeparateDomain>
-
     <AlwaysCompileMarkupFilesInSeparateDomain Condition="'$(AlwaysCompileMarkupFilesInSeparateDomain)' == '' ">true</AlwaysCompileMarkupFilesInSeparateDomain>
-
     <LocalizationDirectivesToLocFile Condition="'$(LocalizationDirectivesToLocFile)' == ''">None</LocalizationDirectivesToLocFile>
-
   </PropertyGroup>
-
-  <UsingTask TaskName="Microsoft.Build.Tasks.Windows.MarkupCompilePass1" AssemblyFile="$(_PresentationBuildTasksAssembly)" />
-  <UsingTask TaskName="Microsoft.Build.Tasks.Windows.UidManager" AssemblyFile="$(_PresentationBuildTasksAssembly)" />
-  <UsingTask TaskName="Microsoft.Build.Tasks.Windows.ResourcesGenerator" AssemblyFile="$(_PresentationBuildTasksAssembly)" />
-  <UsingTask TaskName="Microsoft.Build.Tasks.Windows.FileClassifier" AssemblyFile="$(_PresentationBuildTasksAssembly)" />
-  <UsingTask TaskName="Microsoft.Build.Tasks.Windows.MarkupCompilePass2" AssemblyFile="$(_PresentationBuildTasksAssembly)" />
-  <UsingTask TaskName="Microsoft.Build.Tasks.Windows.GenerateTemporaryTargetAssembly" AssemblyFile="$(_PresentationBuildTasksAssembly)" />
-  <UsingTask TaskName="Microsoft.Build.Tasks.Windows.MergeLocalizationDirectives" AssemblyFile="$(_PresentationBuildTasksAssembly)" />
-
-
+  
   <!-- Some Default Settings -->
   <PropertyGroup>
 

src/Microsoft.DotNet.Wpf/src/PresentationBuildTasks/PresentationBuildTasks.csproj

@@ -44,6 +44,7 @@
     content\targets\ 
   -->
   <ItemGroup>
+    <PackagingContent Include="$(MSBuildThisFileDirectory)Microsoft.WinFx.props" SubFolder="root\targets" />
     <PackagingContent Include="$(MSBuildThisFileDirectory)Microsoft.WinFx.targets" SubFolder="root\targets" />
   </ItemGroup>