Trait attribute_derive::Attribute

pub trait Attribute: Sized {
    type Parser: TryExtendOne + Parse + Default;

    // Required method
    fn from_parser(parser: Self::Parser) -> Result<Self>;

    // Provided methods
    fn from_attributes<'a>(
        attrs: impl IntoIterator<Item = &'a Attribute>
    ) -> Result<Self>
       where Self: AttributeIdent { ... }
    fn remove_attributes(attrs: &mut Vec<Attribute>) -> Result<Self>
       where Self: AttributeIdent { ... }
    fn from_args(tokens: TokenStream) -> Result<Self> { ... }
}

The trait you actually derive on your attribute struct.

Basic gist is a struct like this:

#[derive(Attribute)]
#[attribute(ident = collection)]
#[attribute(error(missing_field = "`{field}` was not specified"))]
struct CollectionAttribute {
    // Options are optional by default (will be set to None if not specified)
    authority: Option<String>,
    name: String,
    // Any type implementing default can be flagged as default
    // This will be set to Vec::default() when not specified
    #[attribute(optional)]
    views: Vec<Type>,
    // Booleans can be used without assiging a value. as a flag.
    // If omitted they are set to false
    some_flag: bool,
}

Will be able to parse an attribute like this:

#[collection(authority="Some String", name = r#"Another string"#, views = [Option, ()], some_flag)]

Required Associated Types

type Parser: TryExtendOne + Parse + Default

Helper struct for storing and parsing attributes

Required Methods

fn from_parser(parser: Self::Parser) -> Result<Self>

Handles conversion from Parser used by the other functions internally

Provided Methods

fn from_attributes<'a>( attrs: impl IntoIterator<Item = &'a Attribute> ) -> Result<Self>where Self: AttributeIdent,

Parses an IntoIterator of syn::Attributes e.g. Vec<Attribute>. Only availible if you specify the attribute ident: #[attribute(ident="<ident>")] when using the derive macro.

It can therefore parse fields set over multiple attributes like:

#[collection(authority = "Authority", name = "Name")]
#[collection(views = [A, B])]

and also catch duplicate/conflicting settings over those.

This is best used for derive macros, where you don’t need to remove your attributes.

Errors

Fails with a syn::Error so you can conveniently return that as a compiler error in a proc macro in the following cases

• A necessary parameter is omitted
• Invalid input is given for a parameter
• A non aggregating parameter is specified multiple times
• An attribute called IDENTS has invalid syntax (e.g. #attr(a: "a"))

fn remove_attributes(attrs: &mut Vec<Attribute>) -> Result<Self>where Self: AttributeIdent,

Parses an &mut Vec<syn::Attributes>. Removing matching attributes. Only availible if you specify an ident: #[attribute(ident="<ident>")] when using the derive macro.

It can therefore parse fields set over multiple attributes like:

#[collection(authority = "Authority", name = "Name")]
#[collection(views = [A, B])]

and also catch duplicate/conflicting settings over those.

Use this if you are implementing an attribute macro, and need to remove your helper attributes.

Errors

Fails with a syn::Error so you can conveniently return that as a compiler error in a proc macro in the following cases

• A necessary parameter is omitted
• Invalid input is given for a parameter
• A non aggregating parameter is specified multiple times
• An attribute called IDENTS has invalid syntax (e.g. #attr(a: "a"))

fn from_args(tokens: TokenStream) -> Result<Self>

Parses a TokenStream.

Useful for implementing general proc macros to parse the input of your macro.

Due to this only parsing the input for a single attribute it is not able to aggregate input spread over multiple attributes.

Errors

Fails with a syn::Error so you can conveniently return that as a compiler error in a proc macro in the following cases

• A necessary parameter is omitted
• Invalid input is given for a parameter
• A non aggregating parameter is specified multiple times

Implementors