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Add documentation for unstable_feature_bound #144676

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Add documentation for unstable_feature_bound
tiif Jul 30, 2025
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tiif Jul 30, 2025
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3 changes: 3 additions & 0 deletions src/doc/rustc-dev-guide/src/stability.md
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Expand Up @@ -183,4 +183,7 @@ the `deprecated_in_future` lint is triggered which is default `allow`, but most
of the standard library raises it to a warning with
`#![warn(deprecated_in_future)]`.

## unstable_feature_bound
The `#[unstable_feature_bound(foo)]` attribute can be used together with `#[unstable]` attribute to mark an `impl` of stable type and stable trait as unstable. In std/core, an item annotated with `#[unstable_feature_bound(foo)]` can only be used by another item that is also annotated with `#[unstable_feature_bound(foo)]`. Outside of std/core, using an item with `#[unstable_feature_bound(foo)]` requires the feature to be enabled with `#![feature(foo)]` attribute on the crate. Currently, only `impl`s and free functions can be annotated with `#[unstable_feature_bound]`.

[blog]: https://www.ralfj.de/blog/2018/07/19/const.html
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