darling_core/options/
outer_from.rs

1use syn::spanned::Spanned;
2use syn::{Field, Ident, Meta};
3
4use crate::ast::Data;
5use crate::codegen::ForwardAttrs;
6use crate::options::{
7    Core, DefaultExpression, ForwardAttrsFilter, ForwardedField, ParseAttribute, ParseData,
8};
9use crate::util::PathList;
10use crate::{Error, FromField, FromMeta, Result};
11
12/// Reusable base for `FromDeriveInput`, `FromVariant`, `FromField`, and other top-level
13/// `From*` traits.
14#[derive(Debug, Clone)]
15pub struct OuterFrom {
16    /// The field on the target struct which should receive the type identifier, if any.
17    pub ident: Option<Ident>,
18
19    /// The field on the target struct which should receive the type attributes, if any.
20    pub attrs: Option<ForwardedField>,
21
22    pub container: Core,
23
24    /// The attribute names that should be searched.
25    pub attr_names: PathList,
26
27    /// The attribute names that should be forwarded. The presence of the word with no additional
28    /// filtering will cause _all_ attributes to be cloned and exposed to the struct after parsing.
29    pub forward_attrs: Option<ForwardAttrsFilter>,
30
31    /// Whether or not the container can be made through conversion from the type `Ident`.
32    pub from_ident: bool,
33}
34
35impl OuterFrom {
36    pub fn start(di: &syn::DeriveInput) -> Result<Self> {
37        Ok(OuterFrom {
38            container: Core::start(di)?,
39            attrs: Default::default(),
40            ident: Default::default(),
41            attr_names: Default::default(),
42            forward_attrs: Default::default(),
43            from_ident: Default::default(),
44        })
45    }
46
47    pub fn as_forward_attrs(&self) -> ForwardAttrs<'_> {
48        ForwardAttrs {
49            field: self.attrs.as_ref(),
50            filter: self.forward_attrs.as_ref(),
51        }
52    }
53}
54
55impl ParseAttribute for OuterFrom {
56    fn parse_nested(&mut self, mi: &Meta) -> Result<()> {
57        let path = mi.path();
58        if path.is_ident("attributes") {
59            self.attr_names = FromMeta::from_meta(mi)?;
60        } else if path.is_ident("forward_attrs") {
61            self.forward_attrs = FromMeta::from_meta(mi)?;
62        } else if path.is_ident("from_ident") {
63            // HACK: Declaring that a default is present will cause fields to
64            // generate correct code, but control flow isn't that obvious.
65            self.container.default = Some(DefaultExpression::Trait {
66                // Use the span of the `from_ident` keyword so that errors in generated code
67                // caused by this will point back to the correct location.
68                span: path.span(),
69            });
70            self.from_ident = true;
71        } else {
72            return self.container.parse_nested(mi);
73        }
74        Ok(())
75    }
76}
77
78impl ParseData for OuterFrom {
79    fn parse_field(&mut self, field: &Field) -> Result<()> {
80        match field.ident.as_ref().map(|v| v.to_string()).as_deref() {
81            Some("ident") => {
82                self.ident.clone_from(&field.ident);
83                Ok(())
84            }
85            Some("attrs") => {
86                self.attrs = ForwardedField::from_field(field).map(Some)?;
87                Ok(())
88            }
89            _ => self.container.parse_field(field),
90        }
91    }
92
93    fn validate_body(&self, errors: &mut crate::error::Accumulator) {
94        self.container.validate_body(errors);
95        if let Some(attrs) = &self.attrs {
96            if self.forward_attrs.is_none() {
97                let container_name = match &self.container.data {
98                    Data::Enum(_) => "enum",
99                    Data::Struct(_) => "struct",
100                };
101                errors.push(
102                    Error::custom(format!(
103                        "field will not be populated because `forward_attrs` is not set on the {}",
104                        container_name
105                    ))
106                    .with_span(&attrs.ident),
107                );
108            }
109        }
110    }
111}
darling_core/options/outer_from.rs

darling_core/options/
outer_from.rs
