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use proc_macro2::Span;
use syn::{
parse::{discouraged::Speculative, Parse, ParseStream, Result},
Attribute, Error, ItemFn, ItemImpl, ItemStatic, ItemTrait,
};
pub enum Item {
Trait(ItemTrait),
Impl(ItemImpl),
Fn(ItemFn),
Static(ItemStatic),
}
macro_rules! fork {
($fork:ident = $input:ident) => {{
$fork = $input.fork();
&$fork
}};
}
impl Parse for Item {
fn parse(input: ParseStream) -> Result<Self> {
let attrs = input.call(Attribute::parse_outer)?;
let mut fork;
let item = if let Some(mut item) = fork!(fork = input).parse::<ItemImpl>().ok() {
if item.trait_.is_none() {
return Err(Error::new(Span::call_site(), "expected a trait impl"));
}
item.attrs = attrs;
Item::Impl(item)
} else if let Some(mut item) = fork!(fork = input).parse::<ItemTrait>().ok() {
item.attrs = attrs;
Item::Trait(item)
} else if let Some(mut item) = fork!(fork = input).parse::<ItemFn>().ok() {
item.attrs = attrs;
Item::Fn(item)
} else if let Some(mut item) = fork!(fork = input).parse::<ItemStatic>().ok() {
item.attrs = attrs;
Item::Static(item)
} else {
return Err(Error::new(
Span::call_site(),
"expected trait impl, trait or fn",
));
};
input.advance_to(&fork);
Ok(item)
}
}
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