darling_core/options/
mod.rs

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1use proc_macro2::Span;
2use syn::{parse_quote, spanned::Spanned};
3
4use crate::ast::NestedMeta;
5use crate::error::Accumulator;
6use crate::{Error, FromMeta, Result};
7
8mod core;
9mod forward_attrs;
10mod forwarded_field;
11mod from_attributes;
12mod from_derive;
13mod from_field;
14mod from_meta;
15mod from_type_param;
16mod from_variant;
17mod input_field;
18mod input_variant;
19mod outer_from;
20mod shape;
21
22pub use self::core::Core;
23pub use self::forward_attrs::ForwardAttrsFilter;
24pub use self::forwarded_field::ForwardedField;
25pub use self::from_attributes::FromAttributesOptions;
26pub use self::from_derive::FdiOptions;
27pub use self::from_field::FromFieldOptions;
28pub use self::from_meta::FromMetaOptions;
29pub use self::from_type_param::FromTypeParamOptions;
30pub use self::from_variant::FromVariantOptions;
31pub use self::input_field::InputField;
32pub use self::input_variant::InputVariant;
33pub use self::outer_from::OuterFrom;
34pub use self::shape::{DataShape, DeriveInputShapeSet};
35
36/// A default/fallback expression encountered in attributes during parsing.
37#[derive(Debug, Clone)]
38pub enum DefaultExpression {
39    /// The value should be taken from the `default` instance of the containing struct.
40    /// This is not valid in container options.
41    Inherit,
42    Explicit(syn::Path),
43    Trait {
44        /// The input span that is responsible for the use of `Default::default`.
45        span: Span,
46    },
47}
48
49#[doc(hidden)]
50impl FromMeta for DefaultExpression {
51    // Note: This cannot use `from_word` as it needs to capture the span
52    // in the `Meta::Path` case.
53    fn from_meta(item: &syn::Meta) -> Result<Self> {
54        match item {
55            syn::Meta::Path(_) => Ok(DefaultExpression::Trait { span: item.span() }),
56            syn::Meta::List(nm) => Err(Error::unsupported_format("list").with_span(nm)),
57            syn::Meta::NameValue(nv) => Self::from_expr(&nv.value),
58        }
59    }
60
61    fn from_expr(expr: &syn::Expr) -> Result<Self> {
62        syn::Path::from_expr(expr).map(DefaultExpression::Explicit)
63    }
64
65    fn from_value(value: &syn::Lit) -> Result<Self> {
66        syn::Path::from_value(value).map(DefaultExpression::Explicit)
67    }
68}
69
70/// Middleware for extracting attribute values. Implementers are expected to override
71/// `parse_nested` so they can apply individual items to themselves, while `parse_attributes`
72/// is responsible for looping through distinct outer attributes and collecting errors.
73pub trait ParseAttribute: Sized {
74    fn parse_attributes(mut self, attrs: &[syn::Attribute]) -> Result<Self> {
75        let mut errors = Error::accumulator();
76        for attr in attrs {
77            if attr.meta.path() == &parse_quote!(darling) {
78                errors.handle(parse_attr(attr, &mut self));
79            }
80        }
81
82        errors.finish_with(self)
83    }
84
85    /// Read a meta-item, and apply its values to the current instance.
86    fn parse_nested(&mut self, mi: &syn::Meta) -> Result<()>;
87}
88
89fn parse_attr<T: ParseAttribute>(attr: &syn::Attribute, target: &mut T) -> Result<()> {
90    let mut errors = Error::accumulator();
91    match &attr.meta {
92        syn::Meta::List(data) => {
93            for item in NestedMeta::parse_meta_list(data.tokens.clone())? {
94                if let NestedMeta::Meta(ref mi) = item {
95                    errors.handle(target.parse_nested(mi));
96                } else {
97                    panic!("Wasn't able to parse: `{:?}`", item);
98                }
99            }
100
101            errors.finish()
102        }
103        item => panic!("Wasn't able to parse: `{:?}`", item),
104    }
105}
106
107/// Middleware for extracting values from the body of the derive input. Implementers are
108/// expected to override `parse_field` or `parse_variant` as appropriate for their use-case,
109/// while `parse_body` dispatches to the appropriate methods and handles error collection.
110pub trait ParseData: Sized {
111    fn parse_body(mut self, body: &syn::Data) -> Result<Self> {
112        use syn::{Data, Fields};
113
114        let mut errors = Error::accumulator();
115
116        match *body {
117            Data::Struct(ref data) => match data.fields {
118                Fields::Unit => {}
119                Fields::Named(ref fields) => {
120                    for field in &fields.named {
121                        errors.handle(self.parse_field(field));
122                    }
123                }
124                Fields::Unnamed(ref fields) => {
125                    for field in &fields.unnamed {
126                        errors.handle(self.parse_field(field));
127                    }
128                }
129            },
130            Data::Enum(ref data) => {
131                for variant in &data.variants {
132                    errors.handle(self.parse_variant(variant));
133                }
134            }
135            Data::Union(_) => unreachable!(),
136        };
137
138        self.validate_body(&mut errors);
139
140        errors.finish_with(self)
141    }
142
143    /// Apply the next found variant to the object, returning an error
144    /// if parsing goes wrong.
145    fn parse_variant(&mut self, variant: &syn::Variant) -> Result<()> {
146        Err(Error::unsupported_format("enum variant").with_span(variant))
147    }
148
149    /// Apply the next found struct field to the object, returning an error
150    /// if parsing goes wrong.
151    fn parse_field(&mut self, field: &syn::Field) -> Result<()> {
152        Err(Error::unsupported_format("struct field").with_span(field))
153    }
154
155    /// Perform validation checks that require data from more than one field or variant.
156    /// The default implementation does no validations.
157    /// Implementors can override this method as appropriate for their use-case.
158    #[allow(unused_variables)]
159    fn validate_body(&self, errors: &mut Accumulator) {}
160}
darling_core/options/mod.rs

darling_core/options/
mod.rs
