darling_core 0.8.3

Helper crate for proc-macro library for reading attributes into structs when implementing custom derives. Use https://crates.io/crates/darling in your code.
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101

use std::ops::Deref;
use std::string::ToString;

use syn::{Ident, Meta, NestedMeta};

use {Error, FromMeta, Result};

/// A list of `syn::Ident` instances. This type is used to extract a list of words from an
/// attribute.
///
/// # Usage
/// An `IdentList` field on a struct implementing `FromMeta` will turn `#[builder(derive(Debug, Clone))]` into:
///
/// ```rust,ignore
/// StructOptions {
///     derive: IdentList(vec![syn::Ident::new("Debug"), syn::Ident::new("Clone")])
/// }
/// ```
#[derive(Debug, Default, Clone, PartialEq, Eq)]
pub struct IdentList(Vec<Ident>);

impl IdentList {
    /// Create a new list.
    pub fn new<T: Into<Ident>>(vals: Vec<T>) -> Self {
        IdentList(vals.into_iter().map(T::into).collect())
    }

    /// Create a new `Vec` containing the string representation of each ident.
    pub fn to_strings(&self) -> Vec<String> {
        self.0.iter().map(ToString::to_string).collect()
    }
}

impl Deref for IdentList {
    type Target = Vec<Ident>;

    fn deref(&self) -> &Self::Target {
        &self.0
    }
}

impl From<Vec<Ident>> for IdentList {
    fn from(v: Vec<Ident>) -> Self {
        IdentList(v)
    }
}

impl FromMeta for IdentList {
    fn from_list(v: &[NestedMeta]) -> Result<Self> {
        let mut idents = Vec::with_capacity(v.len());
        for nmi in v {
            if let NestedMeta::Meta(Meta::Word(ref ident)) = *nmi {
                idents.push(ident.clone());
            } else {
                return Err(Error::unexpected_type("non-word").with_span(nmi));
            }
        }

        Ok(IdentList(idents))
    }
}

#[cfg(test)]
mod tests {
    use super::IdentList;
    use proc_macro2::TokenStream;
    use FromMeta;

    /// parse a string as a syn::Meta instance.
    fn pm(tokens: TokenStream) -> ::std::result::Result<syn::Meta, String> {
        let attribute: syn::Attribute = parse_quote!(#[#tokens]);
        attribute.interpret_meta().ok_or("Unable to parse".into())
    }

    fn fm<T: FromMeta>(tokens: TokenStream) -> T {
        FromMeta::from_meta(&pm(tokens).expect("Tests should pass well-formed input"))
            .expect("Tests should pass valid input")
    }

    #[test]
    fn succeeds() {
        let idents = fm::<IdentList>(quote!(ignore(Debug, Clone, Eq)));
        assert_eq!(
            idents.to_strings(),
            vec![
                String::from("Debug"),
                String::from("Clone"),
                String::from("Eq")
            ]
        );
    }

    /// Check that the parser rejects non-word members of the list, and that the error
    /// has an associated span.
    #[test]
    fn fails_non_word() {
        let input = IdentList::from_meta(&pm(quote!(ignore(Debug, Clone = false))).unwrap());
        let err = input.unwrap_err();
        assert!(err.has_span());
    }
}