Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Add reference for attributes in function parameters #657

Merged
merged 2 commits into from
Oct 19, 2019
Merged

Add reference for attributes in function parameters #657

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
3d1b9ae
Add reference for attributes in function parameters
c410-f3r Sep 29, 2019
1f1fcfb
Add more comments about inert attributes
c410-f3r Oct 18, 2019
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
6 changes: 6 additions & 0 deletions src/attributes.md
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -50,6 +50,9 @@ Attributes may be applied to many things in the language:
* [Generic lifetime or type parameter][generics] accept outer attributes.
* Expressions accept outer attributes in limited situations, see [Expression
Attributes] for details.
* [Function][functions], [closure]] and [function pointer]
parameters accept outer attributes. This includes attributes on variadic parameters
denoted with `...` in function pointers and [external blocks][variadic functions].

Some examples of attributes:

Expand Down Expand Up @@ -306,3 +309,6 @@ The following is an index of all built-in attributes.
[statements]: statements.md
[struct]: items/structs.md
[union]: items/unions.md
[closure]: expressions/closure-expr.md
[function pointer]: types/function-pointer.md
Centril marked this conversation as resolved.
Show resolved Hide resolved
[variadic functions]: items/external-blocks.html#variadic-functions
9 changes: 8 additions & 1 deletion src/expressions/closure-expr.md
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -10,7 +10,7 @@
> &nbsp;&nbsp; _ClosureParam_ (`,` _ClosureParam_)<sup>\*</sup> `,`<sup>?</sup>
>
> _ClosureParam_ :\
> &nbsp;&nbsp; [_Pattern_]&nbsp;( `:` [_Type_] )<sup>?</sup>
> &nbsp;&nbsp; [_OuterAttribute_]<sup>\*</sup> [_Pattern_]&nbsp;( `:` [_Type_] )<sup>?</sup>

A _closure expression_ defines a closure and denotes it as a value, in a single
expression. A closure expression is a pipe-symbol-delimited (`|`) list of
Expand Down Expand Up @@ -67,13 +67,20 @@ let word = "konnichiwa".to_owned();
ten_times(move |j| println!("{}, {}", word, j));
```

## Attributes on closure parameters

Attributes on closure parameters follow the same rules and restrictions as
[regular function parameters].

[block]: block-expr.md
[function definitions]: ../items/functions.md
[patterns]: ../patterns.md
[regular function parameters]: ../items/functions.md#attributes-on-function-parameters

[_Expression_]: ../expressions.md
[_BlockExpression_]: block-expr.md
[_TypeNoBounds_]: ../types.md#type-expressions
[_Pattern_]: ../patterns.md
[_Type_]: ../types.md#type-expressions
[`let` binding]: ../statements.md#let-statements
[_OuterAttribute_]: ../attributes.md
16 changes: 14 additions & 2 deletions src/items/associated-items.md
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -86,8 +86,13 @@ let _: f64 = f64::from_i32(42);
> &nbsp;&nbsp; &nbsp;&nbsp; [_BlockExpression_]
>
> _SelfParam_ :\
> &nbsp;&nbsp; &nbsp;&nbsp; (`&` | `&` [_Lifetime_])<sup>?</sup> `mut`<sup>?</sup> `self`\
> &nbsp;&nbsp; | `mut`<sup>?</sup> `self` (`:` [_Type_])<sup>?</sup>
> &nbsp;&nbsp; [_OuterAttribute_]<sup>\*</sup> ( _ShorthandSelf_ | _TypedSelf_ )
>
> _ShorthandSelf_ :\
> &nbsp;&nbsp; (`&` | `&` [_Lifetime_])<sup>?</sup> `mut`<sup>?</sup> `self`
>
> _TypedSelf_ :\
> &nbsp;&nbsp; `mut`<sup>?</sup> `self` `:` [_Type_]

Associated functions whose first parameter is named `self` are called *methods*
and may be invoked using the [method call operator], for example, `x.foo()`, as
Expand Down Expand Up @@ -190,6 +195,11 @@ let bounding_box = circle_shape.bounding_box();
> methods with anonymous parameters (e.g. `fn foo(u8)`). This is deprecated and
> an error as of the 2018 edition. All parameters must have an argument name.

#### Attributes on method parameters

Attributes on method parameters follow the same rules and restrictions as
[regular function parameters].

## Associated Types

*Associated types* are [type aliases] associated with another type. Associated
Expand Down Expand Up @@ -336,6 +346,7 @@ fn main() {
[`Box<Self>`]: ../special-types-and-traits.md#boxt
[`Pin<P>`]: ../special-types-and-traits.md#pinp
[`Rc<Self>`]: ../special-types-and-traits.md#rct
[_OuterAttribute_]: ../attributes.md
[traits]: traits.md
[type aliases]: type-aliases.md
[inherent implementations]: implementations.md#inherent-implementations
Expand All @@ -349,3 +360,4 @@ fn main() {
[function item]: ../types/function-item.md
[method call operator]: ../expressions/method-call-expr.md
[path]: ../paths.md
[regular function parameters]: functions.md#attributes-on-function-parameters
12 changes: 9 additions & 3 deletions src/items/external-blocks.md
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -24,14 +24,14 @@
> &nbsp;&nbsp; _NamedFunctionParam_ ( `,` _NamedFunctionParam_ )<sup>\*</sup> `,`<sup>?</sup>
>
> _NamedFunctionParam_ :\
> &nbsp;&nbsp; ( [IDENTIFIER] | `_` ) `:` [_Type_]
> &nbsp;&nbsp; [_OuterAttribute_]<sup>\*</sup> ( [IDENTIFIER] | `_` ) `:` [_Type_]
>
> _NamedFunctionParametersWithVariadics_ :\
> &nbsp;&nbsp; ( _NamedFunctionParam_ `,` )<sup>\*</sup> _NamedFunctionParam_ `,` `...`
> &nbsp;&nbsp; ( _NamedFunctionParam_ `,` )<sup>\*</sup> _NamedFunctionParam_ `,` [_OuterAttribute_]<sup>\*</sup> `...`

External blocks provide _declarations_ of items that are not _defined_ in the
current crate and are the basis of Rust's foreign function interface. These are
akin to unchecked imports.
akin to unchecked imports.

Two kind of item _declarations_ are allowed in external blocks: [functions] and
[statics]. Calling functions or accessing statics that are declared in external
Expand Down Expand Up @@ -162,6 +162,11 @@ extern {
}
```

### Attributes on function parameters

Attributes on extern function parameters follow the same rules and
restrictions as [regular function parameters].

[IDENTIFIER]: ../identifiers.md
[WebAssembly module]: https://webassembly.github.io/spec/core/syntax/modules.html
[functions]: functions.md
Expand All @@ -177,3 +182,4 @@ extern {
[_Visibility_]: ../visibility-and-privacy.md
[_WhereClause_]: generics.md#where-clauses
[attributes]: ../attributes.md
[regular function parameters]: functions.md#attributes-on-function-parameters
37 changes: 34 additions & 3 deletions src/items/functions.md
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -17,7 +17,7 @@
> &nbsp;&nbsp; _FunctionParam_ (`,` _FunctionParam_)<sup>\*</sup> `,`<sup>?</sup>
>
> _FunctionParam_ :\
> &nbsp;&nbsp; [_Pattern_] `:` [_Type_]
> &nbsp;&nbsp; [_OuterAttribute_]<sup>\*</sup> [_Pattern_] `:` [_Type_]
>
> _FunctionReturnType_ :\
> &nbsp;&nbsp; `->` [_Type_]
Expand Down Expand Up @@ -244,12 +244,40 @@ fn test_only() {
> Note: Except for lints, it is idiomatic to only use outer attributes on
> function items.

The attributes that have meaning on a function are [`cfg`], [`deprecated`],
The attributes that have meaning on a function are [`cfg`], [`cfg_attr`], [`deprecated`],
[`doc`], [`export_name`], [`link_section`], [`no_mangle`], [the lint check
attributes], [`must_use`], [the procedural macro attributes], [the testing
attributes], and [the optimization hint attributes]. Functions also accept
attributes macros.

## Attributes on function parameters

[Outer attributes][attributes] are allowed on function parameters and the
permitted [built-in attributes] are restricted to `cfg`, `cfg_attr`, `allow`,
Copy link
Contributor

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

I think it would be good to be clearer about exactly which attributes are allowed, since this doesn't mention that (active) proc macros are forbidden. As Centril pointed out in the release notes (and which took me a while to grok until I read rust-lang/rust#63210), that inert helper attributes are allowed. I'm not sure how to word that clearly.

`warn`, `deny`, and `forbid`.

```rust
fn len(
#[cfg(windows)] slice: &[u16],
#[cfg(not(windows))] slice: &[u8],
) -> usize {
slice.len()
}
```

Inert helper attributes used by procedural macro attributes applied to items are also
allowed but be careful to not include these inert attributes in your final `TokenStream`.

For example, the following code defines an inert `some_inert_attribute` attribute that
is not formally defined anywhere and the `some_proc_macro_attribute` procedural macro is
responsible for detecting its presence and removing it from the output token stream.

```rust,ignore
#[some_proc_macro_attribute]
fn foo_oof(#[some_inert_attribute] arg: u8) {
}
```

[IDENTIFIER]: ../identifiers.md
[RAW_STRING_LITERAL]: ../tokens.md#raw-string-literals
[STRING_LITERAL]: ../tokens.md#string-literals
Expand All @@ -258,6 +286,7 @@ attributes macros.
[_Pattern_]: ../patterns.md
[_Type_]: ../types.md#type-expressions
[_WhereClause_]: generics.md#where-clauses
[_OuterAttribute_]: ../attributes.md
[const context]: ../const_eval.md#const-context
[external blocks]: external-blocks.md
[path]: ../paths.md
Expand All @@ -267,7 +296,8 @@ attributes macros.
[*function item type*]: ../types/function-item.md
[Trait]: traits.md
[attributes]: ../attributes.md
[`cfg`]: ../conditional-compilation.md
[`cfg`]: ../conditional-compilation.md#the-cfg-attribute
[`cfg_attr`]: ../conditional-compilation.md#the-cfg_attr-attribute
[the lint check attributes]: ../attributes/diagnostics.md#lint-check-attributes
[the procedural macro attributes]: ../procedural-macros.md
[the testing attributes]: ../attributes/testing.md
Expand All @@ -282,3 +312,4 @@ attributes macros.
[`link_section`]: ../abi.md#the-link_section-attribute
[`no_mangle`]: ../abi.md#the-no_mangle-attribute
[external_block_abi]: external-blocks.md#abi
[built-in attributes]: ../attributes.html#built-in-attributes-index
2 changes: 1 addition & 1 deletion src/items/traits.md
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -38,7 +38,7 @@
> &nbsp;&nbsp; _TraitFunctionParam_ (`,` _TraitFunctionParam_)<sup>\*</sup> `,`<sup>?</sup>
>
> _TraitFunctionParam_<sup>[†](#parameter-patterns)</sup> :\
> &nbsp;&nbsp; ( [_Pattern_] `:` )<sup>?</sup> [_Type_]
> &nbsp;&nbsp; [_OuterAttribute_]<sup>\*</sup> ( [_Pattern_] `:` )<sup>?</sup> [_Type_]
>
> _TraitConst_ :\
> &nbsp;&nbsp; `const` [IDENTIFIER] `:` [_Type_]&nbsp;( `=` [_Expression_] )<sup>?</sup> `;`
Expand Down
11 changes: 9 additions & 2 deletions src/types/function-pointer.md
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -15,10 +15,10 @@
> &nbsp;&nbsp; _MaybeNamedParam_ ( `,` _MaybeNamedParam_ )<sup>\*</sup> `,`<sup>?</sup>
>
> _MaybeNamedParam_ :\
> &nbsp;&nbsp; ( ( [IDENTIFIER] | `_` ) `:` )<sup>?</sup> [_Type_]
> &nbsp;&nbsp; [_OuterAttribute_]<sup>\*</sup> ( ( [IDENTIFIER] | `_` ) `:` )<sup>?</sup> [_Type_]
>
> _MaybeNamedFunctionParametersVariadic_ :\
> &nbsp;&nbsp; ( _MaybeNamedParam_ `,` )<sup>\*</sup> _MaybeNamedParam_ `,` `...`
> &nbsp;&nbsp; ( _MaybeNamedParam_ `,` )<sup>\*</sup> _MaybeNamedParam_ `,` [_OuterAttribute_]<sup>\*</sup> `...`

Function pointer types, written using the `fn` keyword, refer to a function
whose identity is not necessarily known at compile-time. They can be created
Expand All @@ -44,13 +44,20 @@ let bo: Binop = add;
x = bo(5,7);
```

## Attributes on function pointer parameters

Attributes on function pointer parameters follow the same rules and
restrictions as [regular function parameters].

[IDENTIFIER]: ../identifiers.md
[_ForLifetimes_]: ../items/generics.md#where-clauses
[_FunctionQualifiers_]: ../items/functions.md
[_TypeNoBounds_]: ../types.md#type-expressions
[_Type_]: ../types.md#type-expressions
[_OuterAttribute_]: ../attributes.md
[`extern`]: ../items/external-blocks.md
[closures]: closure.md
[extern function]: ../items/functions.md#extern-function-qualifier
[function items]: function-item.md
[unsafe function]: ../unsafe-functions.md
[regular function parameters]: ../items/functions.md#attributes-on-function-parameters