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| <h1 id="feature-gates"><a class="header" href="#feature-gates">Feature gates</a></h1> |
| <p>This chapter is intended to provide basic help for adding, removing, and |
| modifying feature gates.</p> |
| <p>Note that this is specific to <em>language</em> feature gates; <em>library</em> feature gates use <a href="./stability.html">a different |
| mechanism</a>.</p> |
| <h2 id="adding-a-feature-gate"><a class="header" href="#adding-a-feature-gate">Adding a feature gate</a></h2> |
| <p>See <a href="./implementing_new_features.html#stability-in-code">"Stability in code"</a> in the "Implementing new features" section for instructions.</p> |
| <h2 id="removing-a-feature-gate"><a class="header" href="#removing-a-feature-gate">Removing a feature gate</a></h2> |
| <p>To remove a feature gate, follow these steps:</p> |
| <ol> |
| <li> |
| <p>Remove the feature gate declaration in <code>rustc_feature/src/unstable.rs</code>. |
| It will look like this:</p> |
| <pre><code class="language-rust ignore">/// description of feature |
| (unstable, $feature_name, "$version", Some($tracking_issue_number))</code></pre> |
| </li> |
| <li> |
| <p>Add a modified version of the feature gate declaration that you just |
| removed to <code>rustc_feature/src/removed.rs</code>:</p> |
| <pre><code class="language-rust ignore">/// description of feature |
| (removed, $old_feature_name, "$version", Some($tracking_issue_number), |
| Some("$why_it_was_removed"))</code></pre> |
| </li> |
| </ol> |
| <h2 id="renaming-a-feature-gate"><a class="header" href="#renaming-a-feature-gate">Renaming a feature gate</a></h2> |
| <p>To rename a feature gate, follow these steps (the first two are the same steps |
| to follow when <a href="#removing-a-feature-gate">removing a feature gate</a>):</p> |
| <ol> |
| <li> |
| <p>Remove the old feature gate declaration in <code>rustc_feature/src/unstable.rs</code>. |
| It will look like this:</p> |
| <pre><code class="language-rust ignore">/// description of feature |
| (unstable, $old_feature_name, "$version", Some($tracking_issue_number))</code></pre> |
| </li> |
| <li> |
| <p>Add a modified version of the old feature gate declaration that you just |
| removed to <code>rustc_feature/src/removed.rs</code>:</p> |
| <pre><code class="language-rust ignore">/// description of feature |
| /// Renamed to `$new_feature_name` |
| (removed, $old_feature_name, "$version", Some($tracking_issue_number), |
| Some("renamed to `$new_feature_name`"))</code></pre> |
| </li> |
| <li> |
| <p>Add a feature gate declaration with the new name to |
| <code>rustc_feature/src/unstable.rs</code>. It should look very similar to the old |
| declaration:</p> |
| <pre><code class="language-rust ignore">/// description of feature |
| (unstable, $new_feature_name, "$version", Some($tracking_issue_number))</code></pre> |
| </li> |
| </ol> |
| <h2 id="stabilizing-a-feature"><a class="header" href="#stabilizing-a-feature">Stabilizing a feature</a></h2> |
| <p>See <a href="./stabilization_guide.html#updating-the-feature-gate-listing">"Updating the feature-gate listing"</a> in the "Stabilizing Features" chapter |
| for instructions. There are additional steps you will need to take beyond just |
| updating the declaration!</p> |
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