title: C# Extension (OmniSharp) gives false results in VSCode
body: <p>I'm facing some issues using the C# Extension in VSCode. I'm having a basic project set up with one dependency and a Hello World writeline. When I run <code>dotnet run</code>, the project compiles and runs without issue. However, the C# Extension gives me 27 compile problems, all related to System classes. An example is:</p>
  
  <pre><code>Predefined type 'System.String' is not defined or imported (CS0518)
  </code></pre>
  
  <p>...even though System is marked as an <code>Unnecessary using directive. (CS8019)</code>.
  There seems to be a discrepancy between the information <code>dotnet</code> and the extension are giving me. There have been similar issues before which suggest updating VSCode or the extension. That doesn't seem to help unfortunately.</p>
  
  <p>I already tried it without the dependency, that doesn't change anything. It is interesting that I keep getting the message from VSCode that there is an unresolved dependency and I need to "restore". <code>dotnet restore</code> doesn't fix it though.</p>
  
  <p>Example of false problems:</p>
  
  <p><a href="https://i.stack.imgur.com/Pxo0r.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Pxo0r.png" alt="False problems"></a></p>
  
  <p>Project:</p>
  
  <pre><code>&lt;Project Sdk="Microsoft.NET.Sdk"&gt;
  
     &lt;PropertyGroup&gt;
        &lt;OutputType&gt;Exe&lt;/OutputType&gt;
        &lt;TargetFramework&gt;netcoreapp3.0&lt;/TargetFramework&gt;
        &lt;RootNamespace&gt;project&lt;/RootNamespace&gt;
     &lt;/PropertyGroup&gt;
  
     &lt;ItemGroup&gt;
        &lt;PackageReference Include="Hashgraph" Version="3.0.0" /&gt;
     &lt;/ItemGroup&gt;
  
  &lt;/Project&gt;
  </code></pre>
  
  <p>Version of different components:</p>
  
  <pre><code>&gt; dotnet --version
  3.0.100
  &gt; mono --version
  Mono JIT compiler version 6.4.0.198 (tarball Wed Sep 25 00:24:09 BST 2019)
  &gt; msbuild
  Microsoft (R) Build Engine version 16.1.85+gad9c9926a7
  </code></pre>
  
  <p>Edit: I'm on MacOS by the way.</p>