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use crate::{Error, Result};
use std::fmt;
use syn::punctuated::Pair;
use syn::spanned::Spanned;
use syn::{token, Attribute, Meta, MetaList, Path};
/// Try to parse an attribute into a meta list. Path-type meta values are accepted and returned
/// as empty lists with their passed-in path. Name-value meta values and non-meta attributes
/// will cause errors to be returned.
pub fn parse_attribute_to_meta_list(attr: &Attribute) -> Result<MetaList> {
match &attr.meta {
Meta::List(list) => Ok(list.clone()),
Meta::NameValue(nv) => Err(Error::custom(format!(
"Name-value arguments are not supported. Use #[{}(...)]",
DisplayPath(&nv.path)
))
.with_span(&nv)),
Meta::Path(path) => Ok(MetaList {
path: path.clone(),
delimiter: syn::MacroDelimiter::Paren(token::Paren {
span: {
let mut group = proc_macro2::Group::new(
proc_macro2::Delimiter::None,
proc_macro2::TokenStream::new(),
);
group.set_span(attr.span());
group.delim_span()
},
}),
tokens: Default::default(),
}),
}
}
struct DisplayPath<'a>(&'a Path);
impl fmt::Display for DisplayPath<'_> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
let path = self.0;
if path.leading_colon.is_some() {
write!(f, "::")?;
}
for segment in path.segments.pairs() {
match segment {
Pair::Punctuated(segment, _) => write!(f, "{}::", segment.ident)?,
Pair::End(segment) => segment.ident.fmt(f)?,
}
}
Ok(())
}
}
#[cfg(test)]
mod tests {
use super::parse_attribute_to_meta_list;
use crate::ast::NestedMeta;
use syn::spanned::Spanned;
use syn::{parse_quote, Ident};
#[test]
fn parse_list() {
let meta = parse_attribute_to_meta_list(&parse_quote!(#[bar(baz = 4)])).unwrap();
let nested_meta = NestedMeta::parse_meta_list(meta.tokens).unwrap();
assert_eq!(nested_meta.len(), 1);
}
#[test]
fn parse_path_returns_empty_list() {
let meta = parse_attribute_to_meta_list(&parse_quote!(#[bar])).unwrap();
let nested_meta = NestedMeta::parse_meta_list(meta.tokens).unwrap();
assert!(meta.path.is_ident(&Ident::new("bar", meta.path.span())));
assert!(nested_meta.is_empty());
}
#[test]
fn parse_name_value_returns_error() {
parse_attribute_to_meta_list(&parse_quote!(#[bar = 4])).unwrap_err();
}
#[test]
fn parse_name_value_error_includes_example() {
let err = parse_attribute_to_meta_list(&parse_quote!(#[bar = 4])).unwrap_err();
assert!(err.to_string().contains("#[bar(...)]"));
}
}