title: Using import in proto file with Visual Studio/Rider
body: <p>I am getting a "File not found" error when using import in a .proto file.
  I am using Rider but have the same problem when using Visual Studio.</p>
  
  <p><strong>First proto File:</strong></p>
  
  <pre><code>syntax = "proto3";
  
  import "/fileToImport.proto";
  
  service GreeterAPI {
    rpc SayHello (SayHelloRequest) returns (SayHelloResponse);
  }
  
  message SayHelloRequest {
    string name = 1;
  }
  
  message SayHelloResponse {
    string answer = 1;
  }
  </code></pre>
  
  <p><strong>Second proto file that i want to import:</strong></p>
  
  <pre><code>syntax = "proto3";
  
  message Foo {
    string bar = 1;
  }
  </code></pre>
  
  <p>Both files are located next to each other in the project directory.</p>
  
  <p><strong>.csprjo File:</strong></p>
  
  <pre><code>&lt;Project Sdk="Microsoft.NET.Sdk"&gt;
  
      &lt;PropertyGroup&gt;
          &lt;TargetFramework&gt;netcoreapp3.0&lt;/TargetFramework&gt;
      &lt;/PropertyGroup&gt;
  
      &lt;ItemGroup&gt;
        &lt;PackageReference Include="Google.Protobuf" Version="3.10.1" /&gt;
        &lt;PackageReference Include="Grpc.Core" Version="2.25.0" /&gt;
        &lt;PackageReference Include="Grpc.Tools" Version="2.25.0" /&gt;
  
        &lt;Protobuf Include="**/*.proto" /&gt;
      &lt;/ItemGroup&gt;
  
  &lt;/Project&gt;
  </code></pre>
  
  <p>If i build the project without the import line everything is fine. But with the import line i get "File not found"</p>
  
  <p>I know i can use the <code>--proto_path</code> to tell protoc all the files. 
  But i don't want to build an extra pre-build script or something like that.
  I want to use the build in support of the IDE.</p>