Target C# compiler v3.7.0 instead of 3.11.0

This should get it to work on the toolset that shipped with VS 2019 Update 7 instead of requiring Update 11.

Author: AArnott

Directory.Build.props

@@ -26,6 +26,8 @@
     <EmbedUntrackedSources>true</EmbedUntrackedSources>
     <IncludeSymbols Condition=" '$(DebugType)' != 'embedded' ">true</IncludeSymbols>
     <SymbolPackageFormat>snupkg</SymbolPackageFormat>
+
+    <TargetRoslynVersion>3.7.0</TargetRoslynVersion>
   </PropertyGroup>
 
   <ItemGroup>

src/CSharpIsNullAnalyzer.CodeFixes/CSharpIsNullAnalyzer.CodeFixes.csproj

@@ -22,7 +22,7 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.CodeAnalysis" Version="3.11.0" />
+    <PackageReference Include="Microsoft.CodeAnalysis" Version="$(TargetRoslynVersion)" />
     <PackageReference Include="Microsoft.CodeAnalysis.Analyzers" Version="3.3.2" PrivateAssets="all" />
   </ItemGroup>
 

src/CSharpIsNullAnalyzer/CSharpIsNullAnalyzer.csproj

@@ -5,7 +5,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="3.11.0" PrivateAssets="all" />
+    <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="$(TargetRoslynVersion)" PrivateAssets="all" />
     <PackageReference Include="Microsoft.CodeAnalysis.Analyzers" Version="3.3.2" PrivateAssets="all" />
   </ItemGroup>
 

test/CSharpIsNullAnalyzer.Tests/CSharpIsNullAnalyzer.Tests.csproj

@@ -12,7 +12,7 @@
   <ItemGroup>
     <PackageReference Include="coverlet.msbuild" Version="3.1.0" />
     <PackageReference Include="Microsoft.CodeAnalysis.CSharp.CodeFix.Testing.XUnit" Version="1.1.0" />
-    <PackageReference Include="Microsoft.CodeAnalysis.CSharp.Workspaces" version="3.11.0" />
+    <PackageReference Include="Microsoft.CodeAnalysis.CSharp.Workspaces" version="$(TargetRoslynVersion)" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.11.0" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.4.3" />
     <PackageReference Include="xunit" Version="2.4.1" />