Is a contribution clause necessary in dual-licensed MIT-or-Apache code?
<p>I’ve noticed a lot of dual-licensed MIT-or-Apache Rust projects have added <a href="https://github.com/cmr/relicense-assistant/blob/master/issue-template.txt#L53" rel="nofollow noreferrer">this clause</a> concerning contributions:</p>

<pre><code>### Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted
for inclusion in the work by you, as defined in the Apache-2.0 license, shall be
dual licensed as above, without any additional terms or conditions.
</code></pre>

<p>Is this necessary, or is it already covered by the Apache license? Does it change the nature of the license at all?</p>

<p>It does not change the license, but they are alerting you to what you are agreeing to by contributing.</p>

<p>What must be included, under the Apache 2 license, is something similar to this:</p>

<blockquote>
  <p>Copyright [yyyy] [name of copyright owner]</p>
  
  <p>Licensed under the Apache License, Version 2.0 (the "License");
     you may not use this file except in compliance with the License.
     You may obtain a copy of the License at</p>
  
  <p><a href="http://www.apache.org/licenses/LICENSE-2.0" rel="nofollow noreferrer">http://www.apache.org/licenses/LICENSE-2.0</a></p>
  
  <p>Unless required by applicable law or agreed to in writing, software
     distributed under the License is distributed on an "AS IS" BASIS,
     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     See the License for the specific language governing permissions and
     limitations under the License.</p>
</blockquote>

<p><a href="https://opensource.org/licenses/Apache-2.0" rel="nofollow noreferrer">https://opensource.org/licenses/Apache-2.0</a></p>

<p>The license does not say where you have to include that, but you must give notice that you are using the Apache 2 license.</p>

<p>They are giving you the right to opt out by saying "unless you explicitly state otherwise".</p>

<p>You are probably referring to the following clause in Apache License, Version 2.0:</p>

<blockquote>
  <ol start="5">
  <li>Submission of Contributions. Unless You explicitly state otherwise, any Contribution intentionally submitted for inclusion in the Work by You to the Licensor shall be under the terms and conditions of <strong>this License</strong>, without any additional terms or conditions. Notwithstanding the above, nothing herein shall supersede or modify the terms of any separate license agreement you may have executed with Licensor regarding such Contributions.</li>
  </ol>
</blockquote>

<p>It says nothing about whether a contributor would agree to license its contribution under the MIT license in addition to the Apache License, Version 2.0.</p>

copyright software licensing open-source-software