Simplify build authoring required for nullable annotations

Author: AArnott

Directory.Build.props

@@ -29,6 +29,7 @@
     <PackageReference Include="Nerdbank.GitVersioning" Version="3.1.74" PrivateAssets="all" />
     <PackageReference Include="Microsoft.Net.Compilers.Toolset" Version="3.5.0" PrivateAssets="all" />
     <PackageReference Include="StyleCop.Analyzers" Version="1.2.0-beta.164" PrivateAssets="all" />
+    <PackageReference Include="Nullable" Version="1.2.1" PrivateAssets="all" />
   </ItemGroup>
   <ItemGroup>
     <AdditionalFiles Include="$(MSBuildThisFileDirectory)stylecop.json" />

Directory.Build.targets

@@ -17,8 +17,7 @@ public static class Skip
         /// <param name="condition">The condition that must evaluate to <c>true</c> for the test to be skipped.</param>
         /// <param name="reason">The explanation for why the test is skipped.</param>
         public static void If(
-            [DoesNotReturnIf(true)]
-            bool condition,
+            [DoesNotReturnIf(true)] bool condition,
             string? reason = null)
         {
             if (condition)
@@ -33,8 +32,7 @@ public static void If(
         /// <param name="condition">The condition that must evaluate to <c>false</c> for the test to be skipped.</param>
         /// <param name="reason">The explanation for why the test is skipped.</param>
         public static void IfNot(
-            [DoesNotReturnIf(false)]
-            bool condition,
+            [DoesNotReturnIf(false)] bool condition,
             string? reason = null)
         {
             Skip.If(!condition, reason);

src/Xunit.SkippableFact/Skip.cs

@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;netstandard2.1;net45;net452</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net45;net452</TargetFrameworks>
     <RootNamespace>Xunit</RootNamespace>
 
     <Title>Dynamic test skipping for Xunit</Title>
@@ -11,7 +11,7 @@
     <None Update="xunit.runner.json">
       <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
     </None>
-  </ItemGroup>  
+  </ItemGroup>
   <ItemGroup>
     <PackageReference Include="Validation" Version="2.4.18" PrivateAssets="compile;contentfiles;analyzers;build" />
     <PackageReference Include="xunit.extensibility.execution" Version="2.1.0" Condition=" '$(TargetFramework)' == 'net45' " />

src/Xunit.SkippableFact/Xunit.SkippableFact.csproj

@@ -49,7 +49,6 @@ public void IfNot_WithReason()
             }
         }
 
-#if NETCOREAPP3_1
         [Fact]
         public void If_SupportsNullableReferenceTypesPostCondition()
         {
@@ -76,11 +75,10 @@ public void IfNot_SupportsNullableReferenceTypesPostCondition()
                 ? "Not null"
                 : null;
 
-            Skip.IfNot(!(value is null));
+            Skip.IfNot(value is object);
 
             // Does not trigger a nullable reference type warning
             _ = value.Substring(0);
         }
-#endif
     }
 }

test/Xunit.SkippableFact.Tests/SkipTests.cs

@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>net45;net461;netcoreapp2.1;netcoreapp3.1</TargetFrameworks>
+    <TargetFrameworks>net45;net461;netcoreapp2.1</TargetFrameworks>
     <IsPackable>false</IsPackable>
   </PropertyGroup>
   <ItemGroup>