Enhance Roslyn-compiler visible metadata (#21546)

* Move "AdditionalFiles Include="@(AvaloniaXaml)"" to common AvaloniaBuildTasks

* Add AdditionalFiles Include="@(AvaloniaResource)"

* Add a comment

* Add extra CompilerVisibleProperty

* Rename _InjectAvaloniaAdditionalFiles, make it more specific...

* Do not duplicate AdditionalFiles with AvaloniaXaml AvaloniaResource

packages/Avalonia/AvaloniaBuildTasks.targets

@@ -39,6 +39,17 @@
                       Condition="'$(ApplicationIcon)' != ''" />
   </ItemGroup>
 
+  <!-- Include AvaloniaXaml and AvaloniaResource as a Roslyn-visible additional files -->
+  <!-- This is necessary to use these files in source generators and other Roslyn-based extension -->
+  <Target Name="_InjectAvaloniaAdditionalFiles" BeforeTargets="GenerateMSBuildEditorConfigFileShouldRun">
+    <ItemGroup>
+      <AdditionalFiles Include="@(AvaloniaXaml)" SourceItemGroup="AvaloniaXaml" />
+      <_AvaloniaResourceOnly Include="@(AvaloniaResource)"
+                             Exclude="@(AvaloniaXaml)" />
+      <AdditionalFiles Include="@(_AvaloniaResourceOnly)" SourceItemGroup="AvaloniaResource" />
+    </ItemGroup>
+  </Target>
+
   <UsingTask TaskName="GenerateAvaloniaResourcesTask"
              AssemblyFile="$(AvaloniaBuildTasksLocation)"
              />

src/tools/Avalonia.Generators/Avalonia.Generators.props

@@ -9,7 +9,9 @@
     <AvaloniaNameGeneratorAttachDevTools Condition="'$(AvaloniaNameGeneratorAttachDevTools)' == ''">true</AvaloniaNameGeneratorAttachDevTools>
   </PropertyGroup>
   <ItemGroup>
+    <!-- Mark AvaloniaXaml/AvaloniaResource metadata visible for the Roslyn-compiler -->
     <CompilerVisibleItemMetadata Include="AdditionalFiles" MetadataName="SourceItemGroup"/>
+    <!-- Mark Avalonia.Generators config properties visible for the Roslyn-compiler  -->
     <CompilerVisibleProperty Include="AvaloniaNameGeneratorIsEnabled" />
     <CompilerVisibleProperty Include="AvaloniaNameGeneratorBehavior" />
     <CompilerVisibleProperty Include="AvaloniaNameGeneratorDefaultFieldModifier" />
@@ -17,10 +19,9 @@
     <CompilerVisibleProperty Include="AvaloniaNameGeneratorFilterByNamespace" />
     <CompilerVisibleProperty Include="AvaloniaNameGeneratorViewFileNamingStrategy" />
     <CompilerVisibleProperty Include="AvaloniaNameGeneratorAttachDevTools"/>
+    <!-- Mark additional Avalonia properties that might be useful for the Roslyn-compiler -->
+    <CompilerVisibleProperty Include="AvaloniaUseCompiledBindingsByDefault" />
+    <CompilerVisibleProperty Include="AvaloniaMainPackageVersion" />
+    <CompilerVisibleProperty Include="AvaloniaPreviewerNetCoreToolPath" />
   </ItemGroup>
-  <Target Name="_InjectAdditionalFiles" BeforeTargets="GenerateMSBuildEditorConfigFileShouldRun">
-    <ItemGroup>
-      <AdditionalFiles Include="@(AvaloniaXaml)" SourceItemGroup="AvaloniaXaml" />
-    </ItemGroup>
-  </Target>
 </Project>