darling_core/options/
mod.rs

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

darling_core/options/
mod.rs
