title: VS2019, C#, "just-my-code", and DLLs that aren't real
body: <p>I'm using VS 2019, a C# ASP.NET core 3.1 WEB API.</p>
  <p>For reasons (I'll explain if anyone needs them), VS asked me to turn &quot;Just My Code&quot; off. A few hours later, in a different project, I got an <code>System.IO.FileNotFound</code> exception. The problem was a DLL didn't exist. The problem is, that DLL literally doesn't exist, it's not supposed to exist, and it will never exist.</p>
  <p>After turning off Just My Code, I was working on a different project, Project-A (WEB API). It has a project reference to Project-B (Class Library). Project-B uses a NuGet package (Package-C). I wrote all 3 of these things.</p>
  <p>I trigger an endpoint call to Project-A, the controller calls to Project-B, and when B tries to call a method in Package-C, I get a <code>System.IO.FileNotFound</code> exception. It's looking for <code>Package-C.XmlSerializers.dll</code>. But that's not a real thing. As I said, I wrote Package-C, and that DLL just ... isn't a real thing.</p>
  <p>If I turn on &quot;Just My Code&quot; the problem goes away. We have not deployed this code yet, and I'm worried that it won't work on the server. And if it doesn't I don't know how I'm going to provide an imaginary DLL.</p>
  <ul>
  <li>Why is .NET looking for a DLL that doesn't exist and isn't supposed to exist?</li>
  <li>Why is Just My Code triggering this behavior? (I'm not 100% sure what Just My Code does, just a few bits I gleaned before writing this post.)</li>
  </ul>
  <p>Some things that may or may not matter:</p>
  <ul>
  <li><p>I'm running Project-A et al in Debug mode, locally, using IIS Express, and CORS (requests coming from an Angular app being served from VS Code).</p>
  </li>
  <li><p>I recently updated Projects A &amp; B to .net core 3.1, because a co-worker recently updated Package-C to 3.1 (and added some functionality), and I needed the new functionality.</p>
  </li>
  <li><p>Package-C <em>does</em> do XML Deserializing using <code>System.Xml.Serialization</code>; it reads XML from an old SOAP endpoint and deserializes it into a model.</p>
  </li>
  <li><p>I have the out-of-date source code for Package-C on my hard drive (I haven't pulled co-worker's changes yet).</p>
  </li>
  </ul>
  <p>Thank you!</p>