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
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158

use proc_macro2::Span;
use syn::{parse_quote, spanned::Spanned};

use crate::ast::NestedMeta;
use crate::error::Accumulator;
use crate::{Error, FromMeta, Result};

mod core;
mod forward_attrs;
mod from_attributes;
mod from_derive;
mod from_field;
mod from_meta;
mod from_type_param;
mod from_variant;
mod input_field;
mod input_variant;
mod outer_from;
mod shape;

pub use self::core::Core;
pub use self::forward_attrs::{AttrsField, ForwardAttrsFilter};
pub use self::from_attributes::FromAttributesOptions;
pub use self::from_derive::FdiOptions;
pub use self::from_field::FromFieldOptions;
pub use self::from_meta::FromMetaOptions;
pub use self::from_type_param::FromTypeParamOptions;
pub use self::from_variant::FromVariantOptions;
pub use self::input_field::InputField;
pub use self::input_variant::InputVariant;
pub use self::outer_from::OuterFrom;
pub use self::shape::{DataShape, DeriveInputShapeSet};

/// A default/fallback expression encountered in attributes during parsing.
#[derive(Debug, Clone)]
pub enum DefaultExpression {
    /// The value should be taken from the `default` instance of the containing struct.
    /// This is not valid in container options.
    Inherit,
    Explicit(syn::Path),
    Trait {
        /// The input span that is responsible for the use of `Default::default`.
        span: Span,
    },
}

#[doc(hidden)]
impl FromMeta for DefaultExpression {
    // Note: This cannot use `from_word` as it needs to capture the span
    // in the `Meta::Path` case.
    fn from_meta(item: &syn::Meta) -> Result<Self> {
        match item {
            syn::Meta::Path(_) => Ok(DefaultExpression::Trait { span: item.span() }),
            syn::Meta::List(nm) => Err(Error::unsupported_format("list").with_span(nm)),
            syn::Meta::NameValue(nv) => Self::from_expr(&nv.value),
        }
    }

    fn from_expr(expr: &syn::Expr) -> Result<Self> {
        syn::Path::from_expr(expr).map(DefaultExpression::Explicit)
    }

    fn from_value(value: &syn::Lit) -> Result<Self> {
        syn::Path::from_value(value).map(DefaultExpression::Explicit)
    }
}

/// Middleware for extracting attribute values. Implementers are expected to override
/// `parse_nested` so they can apply individual items to themselves, while `parse_attributes`
/// is responsible for looping through distinct outer attributes and collecting errors.
pub trait ParseAttribute: Sized {
    fn parse_attributes(mut self, attrs: &[syn::Attribute]) -> Result<Self> {
        let mut errors = Error::accumulator();
        for attr in attrs {
            if attr.meta.path() == &parse_quote!(darling) {
                errors.handle(parse_attr(attr, &mut self));
            }
        }

        errors.finish_with(self)
    }

    /// Read a meta-item, and apply its values to the current instance.
    fn parse_nested(&mut self, mi: &syn::Meta) -> Result<()>;
}

fn parse_attr<T: ParseAttribute>(attr: &syn::Attribute, target: &mut T) -> Result<()> {
    let mut errors = Error::accumulator();
    match &attr.meta {
        syn::Meta::List(data) => {
            for item in NestedMeta::parse_meta_list(data.tokens.clone())? {
                if let NestedMeta::Meta(ref mi) = item {
                    errors.handle(target.parse_nested(mi));
                } else {
                    panic!("Wasn't able to parse: `{:?}`", item);
                }
            }

            errors.finish()
        }
        item => panic!("Wasn't able to parse: `{:?}`", item),
    }
}

/// Middleware for extracting values from the body of the derive input. Implementers are
/// expected to override `parse_field` or `parse_variant` as appropriate for their use-case,
/// while `parse_body` dispatches to the appropriate methods and handles error collection.
pub trait ParseData: Sized {
    fn parse_body(mut self, body: &syn::Data) -> Result<Self> {
        use syn::{Data, Fields};

        let mut errors = Error::accumulator();

        match *body {
            Data::Struct(ref data) => match data.fields {
                Fields::Unit => {}
                Fields::Named(ref fields) => {
                    for field in &fields.named {
                        errors.handle(self.parse_field(field));
                    }
                }
                Fields::Unnamed(ref fields) => {
                    for field in &fields.unnamed {
                        errors.handle(self.parse_field(field));
                    }
                }
            },
            Data::Enum(ref data) => {
                for variant in &data.variants {
                    errors.handle(self.parse_variant(variant));
                }
            }
            Data::Union(_) => unreachable!(),
        };

        self.validate_body(&mut errors);

        errors.finish_with(self)
    }

    /// Apply the next found variant to the object, returning an error
    /// if parsing goes wrong.
    fn parse_variant(&mut self, variant: &syn::Variant) -> Result<()> {
        Err(Error::unsupported_format("enum variant").with_span(variant))
    }

    /// Apply the next found struct field to the object, returning an error
    /// if parsing goes wrong.
    fn parse_field(&mut self, field: &syn::Field) -> Result<()> {
        Err(Error::unsupported_format("struct field").with_span(field))
    }

    /// Perform validation checks that require data from more than one field or variant.
    /// The default implementation does no validations.
    /// Implementors can override this method as appropriate for their use-case.
    #[allow(unused_variables)]
    fn validate_body(&self, errors: &mut Accumulator) {}
}