Add build script logic to facilitate the test switchover to [Fact] style

This change is based on Jeremy's POC PR; I have modified the build
scripts to minimize the changes to the individual test build scripts.
In the simplest case the conversion requires just replacing the Main
method with a [Fact]-marked test entrypoint and removing the
OutputType property from the project file.

Empty OutputType property gets automatically replaced with the Library
default in the SDK scripts; this is not a huge deal but I had to
remove the pre-existing hack of OutputType=Library + CLRTestKind=""
implying SharedLibrary. According to my search most Library projects
already have the SharedLibrary CLRTestKind set, for the rest I plan
to set it using a bulk project modification; I think I should be able
to adapt the ILTransform analyzer for this purpose.

Thanks

Tomas

src/tests/Common/CoreCLRTestLibrary/CoreCLRTestLibrary.csproj

@@ -15,6 +15,10 @@
     <Compile Include="Utilities.cs" />
     <Compile Include="HostPolicyMock.cs" />
     <Compile Include="XPlatformUtils.cs" />
+
+    <!-- xUnit-style attribute support -->
+    <Compile Include="SkipOnPlatformAttribute.cs" />
+    <Compile Include="TestPlatforms.cs" />
   </ItemGroup>
 
 </Project>

src/tests/Common/CoreCLRTestLibrary/SkipOnPlatformAttribute.cs

@@ -0,0 +1,15 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+//
+
+using System;
+
+namespace Xunit
+{
+    [AttributeUsage(AttributeTargets.Assembly | AttributeTargets.Class | AttributeTargets.Method, AllowMultiple = true, Inherited = true)]
+    public class SkipOnPlatformAttribute : Attribute
+    {
+        internal SkipOnPlatformAttribute() { }
+        public SkipOnPlatformAttribute(TestPlatforms testPlatforms, string reason) { }
+    }
+}

src/tests/Common/CoreCLRTestLibrary/TestPlatforms.cs

@@ -0,0 +1,27 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+//
+
+using System;
+
+namespace Xunit
+{
+    [Flags]
+    public enum TestPlatforms
+    {
+        Windows = 1,
+        Linux = 2,
+        OSX = 4,
+        FreeBSD = 8,
+        NetBSD = 16,
+        illumos= 32,
+        Solaris = 64,
+        iOS = 128,
+        tvOS = 256,
+        Android = 512,
+        Browser = 1024,
+        MacCatalyst = 2048,
+        AnyUnix = FreeBSD | Linux | NetBSD | OSX | illumos | Solaris | iOS | tvOS | MacCatalyst | Android | Browser,
+        Any = ~0
+    }
+}

src/tests/Directory.Build.targets

@@ -11,9 +11,14 @@
 
   <!-- Default priority building values. -->
   <PropertyGroup>
-    <CLRTestKind Condition="'$(CLRTestKind)' == '' and '$(OutputType)' == 'Library'">SharedLibrary</CLRTestKind>
     <CLRTestKind Condition="'$(CLRTestKind)' == ''">BuildAndRun</CLRTestKind>
     <CLRTestPriority Condition="'$(CLRTestPriority)' == ''">0</CLRTestPriority>
+
+    <IsFactStyleTest>false</IsFactStyleTest>
+    <IsFactStyleTest Condition="'$(OutputType)' == 'Library' and '$(CLRTestKind)' == 'BuildAndRun'">true</IsFactStyleTest>
+
+    <!-- Switch OutputType to exe, otherwise Roslyn fails to compile the Main method in the generated wrapper -->
+    <OutputType Condition="$(IsFactStyleTest)">exe</OutputType>
   </PropertyGroup>
 
   <!-- All CLRTests need to be of a certain "kind". These kinds are enumerated below.
@@ -74,6 +79,13 @@
     </ProjectReference>
   </ItemGroup>
 
+  <!-- Inject the XUnit wrapper generator into test build for [Fact]-style tests -->
+  <ItemGroup Condition="$(IsFactStyleTest)">
+    <ProjectReference Include="$(MSBuildThisFileDirectory)/Common/XUnitWrapperGenerator/XUnitWrapperGenerator.csproj" OutputItemType="Analyzer" ReferenceOutputAssembly="false" />
+  </ItemGroup>
+
+  <Import Project="Common/XUnitWrapperGenerator/XUnitWrapperGenerator.props" Condition="$(IsFactStyleTest)" />
+
   <!-- Determine if this project should be built or not -->
   <PropertyGroup>
     <BuildAllProjects Condition="'$(BuildAllProjects)' == ''">false</BuildAllProjects>

src/tests/Interop/PInvoke/Decimal/DecimalTest.cs

@@ -6,35 +6,6 @@
 using TestLibrary;
 using FactAttribute = Xunit.FactAttribute;
 
-namespace Xunit
-{
-    [AttributeUsage(AttributeTargets.Assembly | AttributeTargets.Class | AttributeTargets.Method, AllowMultiple = true, Inherited = true)]
-    public class SkipOnPlatformAttribute : Attribute
-    {
-        internal SkipOnPlatformAttribute() { }
-        public SkipOnPlatformAttribute(TestPlatforms testPlatforms, string reason) { }
-    }
-
-    [Flags]
-    public enum TestPlatforms
-    {
-        Windows = 1,
-        Linux = 2,
-        OSX = 4,
-        FreeBSD = 8,
-        NetBSD = 16,
-        illumos= 32,
-        Solaris = 64,
-        iOS = 128,
-        tvOS = 256,
-        Android = 512,
-        Browser = 1024,
-        MacCatalyst = 2048,
-        AnyUnix = FreeBSD | Linux | NetBSD | OSX | illumos | Solaris | iOS | tvOS | MacCatalyst | Android | Browser,
-        Any = ~0
-    }
-}
-
 public class DecimalTest
 {
     private const int StartingIntValue = 42;

src/tests/Interop/PInvoke/Decimal/DecimalTest.csproj

@@ -1,14 +1,8 @@
 <Project Sdk="Microsoft.NET.Sdk">
-  <PropertyGroup>
-    <OutputType>Exe</OutputType>
-  </PropertyGroup>
   <ItemGroup>
     <Compile Include="*.cs" />
   </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="CMakeLists.txt" />
-    <ProjectReference Include="$(RepoRoot)/src/tests/Common/XUnitWrapperGenerator/XUnitWrapperGenerator.csproj" OutputItemType="Analyzer" ReferenceOutputAssembly="false" />
   </ItemGroup>
-
-  <Import Project="$(RepoRoot)/src/tests/Common/XUnitWrapperGenerator/XUnitWrapperGenerator.props" />
 </Project>