Allow authoring scenarios to make use of abstract classes in their im…

…plementation (#1512)

* Allow abstract class as base class for authored types by making them an implementation detail that is not projected given abstract classes aren't projected in WinRT

* Add test case

* Move setting of CsWinRTWindowsMetadata to the property group not within a target so that the WinRT component source generator can also pick it up

nuget/Microsoft.Windows.CsWinRT.targets

@@ -35,6 +35,8 @@ Copyright (C) Microsoft Corporation. All rights reserved.
  <CsWinRTExeTFM Condition="$([MSBuild]::GetTargetFrameworkVersion('$(TargetFramework)')) == 7">net7.0</CsWinRTExeTFM>
  <CsWinRTExeTFM Condition="$([MSBuild]::GetTargetFrameworkVersion('$(TargetFramework)')) >= 8">net8.0</CsWinRTExeTFM>
  <CsWinRTExeTFM Condition="'$(CsWinRTExeTFM)' == ''">netstandard2.0</CsWinRTExeTFM>
+ <CsWinRTWindowsMetadata Condition="'$(CsWinRTWindowsMetadata)' == ''">$(WindowsSDKVersion.TrimEnd('\'))</CsWinRTWindowsMetadata>
+ <CsWinRTWindowsMetadata Condition="'$(CsWinRTWindowsMetadata)' == ''">$(TargetPlatformVersion)</CsWinRTWindowsMetadata>
  </PropertyGroup>
 
  <ItemGroup>
@@ -114,8 +116,6 @@ Copyright (C) Microsoft Corporation. All rights reserved.
  -->
  <CsWinRTCommand>"$(CsWinRTExe)" %40"$(CsWinRTResponseFile)"</CsWinRTCommand>
  <CsWinRTCommandPrivateProjection>"$(CsWinRTExe)" %40"$(CsWinRTResponseFilePrivateProjection)"</CsWinRTCommandPrivateProjection>
- <CsWinRTWindowsMetadata Condition="'$(CsWinRTWindowsMetadata)' == ''">$(WindowsSDKVersion.TrimEnd('\'))</CsWinRTWindowsMetadata>
- <CsWinRTWindowsMetadata Condition="'$(CsWinRTWindowsMetadata)' == ''">$(TargetPlatformVersion)</CsWinRTWindowsMetadata>
  <CsWinRTWindowsMetadataInput Condition="'$(CsWinRTWindowsMetadata)' != ''">-input $(CsWinRTWindowsMetadata)</CsWinRTWindowsMetadataInput>
  </PropertyGroup>
 

src/Authoring/WinRT.SourceGenerator/WinRTTypeWriter.cs

@@ -2016,7 +2016,9 @@ void AddComponentType(INamedTypeSymbol type, Action visitTypeDeclaration = null)
  TypeAttributes.BeforeFieldInit;
 
  // extends
- if (type.BaseType != null)
+ // WinRT doesn't support projecting abstract classes.
+ // If the base class is one, ignore it.
+ if (type.BaseType != null && !type.BaseType.IsAbstract)
  {
  baseType = GetTypeReference(type.BaseType);
  }

src/Tests/AuthoringTest/Program.cs

@@ -1474,6 +1474,10 @@ bool IDictionary<string, int>.TryGetValue(string key, out int value)
  }
  }
 
+ public sealed class TestCollection : CollectionBase
+ {
+ }
+
  public partial interface IPartialInterface
  {
  public string GetNumberAsString();