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