darling_core/util/
parse_attribute.rs

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1use crate::{Error, Result};
2use std::fmt;
3use syn::punctuated::Pair;
4use syn::spanned::Spanned;
5use syn::{token, Attribute, Meta, MetaList, Path};
6
7/// Try to parse an attribute into a meta list. Path-type meta values are accepted and returned
8/// as empty lists with their passed-in path. Name-value meta values and non-meta attributes
9/// will cause errors to be returned.
10pub fn parse_attribute_to_meta_list(attr: &Attribute) -> Result<MetaList> {
11    match &attr.meta {
12        Meta::List(list) => Ok(list.clone()),
13        Meta::NameValue(nv) => Err(Error::custom(format!(
14            "Name-value arguments are not supported. Use #[{}(...)]",
15            DisplayPath(&nv.path)
16        ))
17        .with_span(&nv)),
18        Meta::Path(path) => Ok(MetaList {
19            path: path.clone(),
20            delimiter: syn::MacroDelimiter::Paren(token::Paren {
21                span: {
22                    let mut group = proc_macro2::Group::new(
23                        proc_macro2::Delimiter::None,
24                        proc_macro2::TokenStream::new(),
25                    );
26                    group.set_span(attr.span());
27                    group.delim_span()
28                },
29            }),
30            tokens: Default::default(),
31        }),
32    }
33}
34
35struct DisplayPath<'a>(&'a Path);
36
37impl fmt::Display for DisplayPath<'_> {
38    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
39        let path = self.0;
40        if path.leading_colon.is_some() {
41            write!(f, "::")?;
42        }
43        for segment in path.segments.pairs() {
44            match segment {
45                Pair::Punctuated(segment, _) => write!(f, "{}::", segment.ident)?,
46                Pair::End(segment) => segment.ident.fmt(f)?,
47            }
48        }
49
50        Ok(())
51    }
52}
53
54#[cfg(test)]
55mod tests {
56    use super::parse_attribute_to_meta_list;
57    use crate::ast::NestedMeta;
58    use syn::spanned::Spanned;
59    use syn::{parse_quote, Ident};
60
61    #[test]
62    fn parse_list() {
63        let meta = parse_attribute_to_meta_list(&parse_quote!(#[bar(baz = 4)])).unwrap();
64        let nested_meta = NestedMeta::parse_meta_list(meta.tokens).unwrap();
65        assert_eq!(nested_meta.len(), 1);
66    }
67
68    #[test]
69    fn parse_path_returns_empty_list() {
70        let meta = parse_attribute_to_meta_list(&parse_quote!(#[bar])).unwrap();
71        let nested_meta = NestedMeta::parse_meta_list(meta.tokens).unwrap();
72        assert!(meta.path.is_ident(&Ident::new("bar", meta.path.span())));
73        assert!(nested_meta.is_empty());
74    }
75
76    #[test]
77    fn parse_name_value_returns_error() {
78        parse_attribute_to_meta_list(&parse_quote!(#[bar = 4])).unwrap_err();
79    }
80
81    #[test]
82    fn parse_name_value_error_includes_example() {
83        let err = parse_attribute_to_meta_list(&parse_quote!(#[bar = 4])).unwrap_err();
84        assert!(err.to_string().contains("#[bar(...)]"));
85    }
86}
darling_core/util/parse_attribute.rs

darling_core/util/
parse_attribute.rs
