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Update docs for deprecated attribute #1338

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May 12, 2022
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Update docs for deprecated attribute #1338

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33 changes: 15 additions & 18 deletions src/stability.md
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Expand Up @@ -121,38 +121,35 @@ Always ping @rust-lang/wg-const-eval if you are adding more

## staged_api

Any crate that uses the `stable`, `unstable`, or `rustc_deprecated` attributes
must include the `#![feature(staged_api)]` attribute on the crate.
Any crate that uses the `stable` or `unstable` attributes must include the
`#![feature(staged_api)]` attribute on the crate.

## rustc_deprecated
## deprecated

The deprecation system shares the same infrastructure as the stable/unstable
attributes. The `rustc_deprecated` attribute is similar to the [`deprecated`
attribute]. It was previously called `deprecated`, but was split off when
`deprecated` was stabilized. The `deprecated` attribute cannot be used in a
`staged_api` crate, `rustc_deprecated` must be used instead. The deprecated
item must also have a `stable` or `unstable` attribute.
Deprecations in the standard library are nearly identical to deprecations in
user code. When `#[deprecated]` is used on an item, it must also have a `stable`
or `unstable `attribute.

`rustc_deprecated` has the following form:
`deprecated` has the following form:

```rust,ignore
#[rustc_deprecated(
#[deprecated(
since = "1.38.0",
reason = "explanation for deprecation",
note = "explanation for deprecation",
suggestion = "other_function"
)]
```

The `suggestion` field is optional. If given, it should be a string that can be
used as a machine-applicable suggestion to correct the warning. This is
typically used when the identifier is renamed, but no other significant changes
are necessary.
are necessary. When the `suggestion` field is used, you need to have
`#![feature(deprecated_suggestion)]` at the crate root.

Another difference from the `deprecated` attribute is that the `since` field is
actually checked against the current version of `rustc`. If `since` is in a
future version, then the `deprecated_in_future` lint is triggered which is
default `allow`, but most of the standard library raises it to a warning with
Another difference from user code is that the `since` field is actually checked
against the current version of `rustc`. If `since` is in a future version, then
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)]`.

[`deprecated` attribute]: https://doc.rust-lang.org/reference/attributes/diagnostics.html#the-deprecated-attribute
[blog]: https://www.ralfj.de/blog/2018/07/19/const.html