Rollup merge of #88057 - ehuss:releases-doc-macros, r=Mark-Simulacrum

Update RELEASES to clarify attribute macro values.

As noted in #87681, macros do not work with the `#[path]` attribute.  Since the places where macros *can* be used is very limited, I have changed this to just focus on `#[doc]` which is the only attribute where this is really useful.
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Jack Huey 2021-08-21 20:56:28 -04:00 committed by GitHub
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@ -146,18 +146,13 @@ Version 1.54.0 (2021-07-29)
Language
-----------------------
- [You can now use macros for values in built-in attribute macros.][83366]
While a seemingly minor addition on its own, this enables a lot of
powerful functionality when combined correctly. Most notably you can
now include external documentation in your crate by writing the following.
- [You can now use macros for values in some built-in attributes.][83366]
This primarily allows you to call macros within the `#[doc]` attribute. For
example, to include external documentation in your crate, you can now write
the following:
```rust
#![doc = include_str!("README.md")]
```
You can also use this to include auto-generated modules:
```rust
#[path = concat!(env!("OUT_DIR"), "/generated.rs")]
mod generated;
```
- [You can now cast between unsized slice types (and types which contain
unsized slices) in `const fn`.][85078]