3 releases
0.1.9 | May 12, 2022 |
---|---|
0.1.8 | Oct 17, 2021 |
0.1.7 | Oct 17, 2021 |
#1491 in Procedural macros
1,142 downloads per month
Used in 15 crates
(4 directly)
7KB
better-bae
This crate is a fork of
bae
better-bae
is a crate for proc macro authors, which simplifies parsing of attributes. It is heavily inspired by darling
but has a significantly simpler API.
See the docs for more info.
lib.rs
:
This crate is a fork of bae
.
better-bae
is a crate for proc macro authors, which simplifies parsing of attributes. It is
heavily inspired by darling
but has a significantly
simpler API.
use better_bae::FromAttributes;
#[derive(
Debug,
Eq,
PartialEq,
// This will add two functions:
// ```
// fn from_attributes(attrs: &[syn::Attribute]) -> Result<MyAttr, syn::Error>
// fn try_from_attributes(attrs: &[syn::Attribute]) -> Result<Option<MyAttr>, syn::Error>
// ```
//
// `try_from_attributes` returns `Ok(None)` if the attribute is missing, `Ok(Some(_))` if
// its there and is valid, `Err(_)` otherwise.
FromAttributes,
)]
pub struct MyAttr {
// Anything that implements `syn::parse::Parse` is supported.
mandatory_type: syn::Type,
mandatory_ident: syn::Ident,
// Fields wrapped in `Option` are optional and default to `None` if
// not specified in the attribute.
optional_missing: Option<syn::Type>,
optional_given: Option<syn::Type>,
// A "switch" is something that doesn't take arguments.
// All fields with type `Option<()>` are considered swiches.
// They default to `None`.
switch: Option<()>,
}
// `MyAttr` is now equipped to parse attributes named `my_attr`. For example:
//
// #[my_attr(
// switch,
// mandatory_ident = foo,
// mandatory_type = SomeType,
// optional_given = OtherType,
// )]
// struct Foo {
// ...
// }
// the input and output type would normally be `proc_macro::TokenStream` but those
// types cannot be used outside the compiler itself.
fn my_proc_macro(input: proc_macro2::TokenStream) -> proc_macro2::TokenStream {
let item_struct = syn::parse2::<syn::ItemStruct>(input).unwrap();
let my_attr = MyAttr::from_attributes(&item_struct.attrs).unwrap();
assert_eq!(
my_attr.mandatory_type,
syn::parse_str::<syn::Type>("SomeType").unwrap()
);
assert_eq!(my_attr.optional_missing, None);
assert_eq!(
my_attr.optional_given,
Some(syn::parse_str::<syn::Type>("OtherType").unwrap())
);
assert_eq!(my_attr.mandatory_ident, syn::parse_str::<syn::Ident>("foo").unwrap());
assert_eq!(my_attr.switch.is_some(), true);
// ...
#
# quote::quote! {}
}
#
Dependencies
~1.5MB
~36K SLoC