title: Rider suggests to use C# 8 syntax but then fails to build solution
body: <p>Rider suggests to use C# 8 syntax, such as <a href="https://docs.microsoft.com/en-us/dotnet/csharp/whats-new/csharp-8#using-declarations" rel="nofollow noreferrer">using declaration</a> or <a href="https://docs.microsoft.com/en-us/dotnet/csharp/whats-new/csharp-8#asynchronous-streams" rel="nofollow noreferrer">async streams</a>.</p>
  
  <p>However, when I apply the recommended refactor, build fails on syntax errors.</p>
  
  <p>My <code>csproj.DotSettings</code> file contains the language level set to <code>latest</code>:</p>
  
  <pre><code>&lt;wpf:ResourceDictionary xml:space="preserve" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:s="clr-namespace:System;assembly=mscorlib" xmlns:ss="urn:shemas-jetbrains-com:settings-storage-xaml" xmlns:wpf="http://schemas.microsoft.com/winfx/2006/xaml/presentation"&gt;
      &lt;s:String x:Key="/Default/CodeInspection/CSharpLanguageProject/LanguageLevel/@EntryValue"&gt;latest&lt;/s:String&gt;
  ...
  &lt;/wpf:ResourceDictionary&gt;
  </code></pre>
  
  <p>To clarify - I'm all for using C# 8. Where can I set the compiler target language? Or could it be just not supported yet?</p>
  
  <p>In my project properties:</p>
  
  <p><a href="https://i.stack.imgur.com/RrEXP.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/RrEXP.png" alt="props"></a></p>
  
  <p><a href="https://i.stack.imgur.com/0NkSX.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/0NkSX.png" alt="props"></a></p>