title: warn unused_doc_comments for macros
body: <p>How can I add and use doc comments with a macro invocation?</p>
  <pre><code>macro_rules! foo {
  (
      $(#[$outer:meta])*
      $name:ident
  ) =&gt; {
          pub mod $name {
              $(#[$outer])*
              pub const THE_ANSWER: i32 = 42;
          }
      }
  }
  
  /// doc for macro created module
  foo!(bar);
  
  fn main() {
      println!(&quot;{}&quot;, bar::THE_ANSWER);
  }
  </code></pre>
  <p><a href="https://play.rust-lang.org/?version=stable&amp;mode=debug&amp;edition=2018&amp;gist=36168f4e7650b3ef21a16f119d37c8bf" rel="nofollow noreferrer">Playground Link</a></p>
  <p>I seem to be doing what's recommended by <a href="https://stackoverflow.com/questions/33999341/generating-documentation-in-macros">this question</a> but I still get the warning.</p>
  <pre><code>warning: unused doc comment
     --&gt; src/main.rs:13:1
     |
  13 | /// doc for macro created module
     | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ rustdoc does not generate documentation for macro invocations
     |
     = note: `#[warn(unused_doc_comments)]` on by default
     = help: to document an item produced by a macro, the macro must produce the documentation as part of its expansion
  </code></pre>