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Merged
merged 4 commits into from
Oct 23, 2025
+40 −37
Merged

Minor adjustments to inner/outer attribute definitions #2059

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654dfb1
Split outer attribute definition to a dedicated rule
ehuss Oct 23, 2025
85d7f5c
Unwrap inner/outer attribute
ehuss Oct 23, 2025
d6b2e6e
Use the terminology "form" for attribute definitions
ehuss Oct 23, 2025
8d56c5d
Move attribute examples to earlier in the chapter
ehuss Oct 23, 2025
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77 changes: 40 additions & 37 deletions src/attributes.md
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Expand Up @@ -23,9 +23,44 @@ to name, convention, language, and compiler version. Attributes are modeled
on Attributes in [ECMA-335], with the syntax coming from [ECMA-334] \(C#).

r[attributes.inner]
_Inner attributes_, written with a bang (`!`) after the hash (`#`), apply to the
item that the attribute is declared within. _Outer attributes_, written without
the bang after the hash, apply to the thing that follows the attribute.
_Inner attributes_, written with a bang (`!`) after the hash (`#`), apply to the form that the attribute is declared within.

> [!EXAMPLE]
> ```rust
> // General metadata applied to the enclosing module or crate.
> #![crate_type = "lib"]
>
> // Inner attribute applies to the entire function.
> fn some_unused_variables() {
> #![allow(unused_variables)]
>
> let x = ();
> let y = ();
> let z = ();
> }
> ```

r[attributes.outer]
_Outer attributes_, written without the bang after the hash, apply to the form that follows the attribute.

> [!EXAMPLE]
> ```rust
> // A function marked as a unit test
> #[test]
> fn test_foo() {
> /* ... */
> }
>
> // A conditionally-compiled module
> #[cfg(target_os = "linux")]
> mod bar {
> /* ... */
> }
>
> // A lint attribute used to suppress a warning/error
> #[allow(non_camel_case_types)]
> type int8_t = i8;
> ```

r[attributes.input]
The attribute consists of a path to the attribute, followed by an optional
Expand Down Expand Up @@ -56,7 +91,7 @@ Attributes can be classified into the following kinds:
* [Tool attributes](#tool-attributes)

r[attributes.allowed-position]
Attributes may be applied to many things in the language:
Attributes may be applied to many forms in the language:

* All [item declarations] accept outer attributes while [external blocks],
[functions], [implementations], and [modules] accept inner attributes.
Expand All @@ -74,38 +109,6 @@ Attributes may be applied to many things in the language:
parameters accept outer attributes. This includes attributes on variadic parameters
denoted with `...` in function pointers and [external blocks][variadic functions].

Some examples of attributes:

```rust
// General metadata applied to the enclosing module or crate.
#![crate_type = "lib"]

// A function marked as a unit test
#[test]
fn test_foo() {
/* ... */
}

// A conditionally-compiled module
#[cfg(target_os = "linux")]
mod bar {
/* ... */
}

// A lint attribute used to suppress a warning/error
#[allow(non_camel_case_types)]
type int8_t = i8;

// Inner attribute applies to the entire function.
fn some_unused_variables() {
#![allow(unused_variables)]

let x = ();
let y = ();
let z = ();
}
```

r[attributes.meta]
## Meta item attribute syntax

Expand Down Expand Up @@ -196,7 +199,7 @@ r[attributes.activity]

r[attributes.activity.intro]
An attribute is either active or inert. During attribute processing, *active
attributes* remove themselves from the thing they are on while *inert attributes*
attributes* remove themselves from the form they are on while *inert attributes*
stay on.

The [`cfg`] and [`cfg_attr`] attributes are active.
Expand Down