title: Is it possible to mark an assembly as deprecated?
body: <p>I'd like to produce a warning message when users compile code that references an assembly we're planning on removing. The contents of this assembly have been merged with another, and I'd like to encourage users to stop referencing the old assembly.</p>
  
  <p>Unfortunately, it looks like ObsoleteAttribute is not valid for assemblies. Is there any other way to cause a compiler warning when a project referencing an assembly is built?</p>
  
  <p>Thanks.</p>
  
  <p>EDIT: For clarification, here's what the assemblies look like before and after the merge</p>
  
  <p>Before the merge:</p>
  
  <pre><code>Assembly1:
  namespace A.B.C {
      class C1
      ...
  }
  
  Assembly2:
  namespace A.B.D {
      class D1
      ...
  }
  </code></pre>
  
  <p>After the merge:</p>
  
  <pre><code>Assembly1:
  (empty)
  
  Assembly2:
  namespace A.B.C {
      class C1
      ...
  }
  
  namespace A.B.D {
      class D1
      ...
  }
  </code></pre>
  
  <p>Before the merge, users referenced both Assembly1 and Assembly2. After the merge, they only need to reference Assembly2, but I'd rather produce a warning that Assembly1 is no longer necessary than break their builds by removing Assembly1 right away.</p>
  
  <p>It sounds like I should use type forwarders to make sure that programs that have already been built against these assemblies continue to work without requiring recompilation, but I don't want to leave stub classes in Assembly1 just to flag the assembly as obsolete.</p>