darling_core/options/
outer_from.rs

1use quote::ToTokens;
2use syn::spanned::Spanned;
3use syn::{Field, Ident, Meta};
4
5use crate::ast::Data;
6use crate::codegen::ForwardAttrs;
7use crate::options::{
8    Core, DefaultExpression, ForwardAttrsFilter, ForwardedField, ParseAttribute, ParseData,
9};
10use crate::util::PathList;
11use crate::{Error, FromField, FromMeta, Result};
12
13/// Reusable base for `FromDeriveInput`, `FromVariant`, `FromField`, and other top-level
14/// `From*` traits.
15#[derive(Debug, Clone)]
16pub struct OuterFrom {
17    /// The field on the target struct which should receive the type identifier, if any.
18    pub ident: Option<Ident>,
19
20    /// The field on the target struct which should receive the type attributes, if any.
21    pub attrs: Option<ForwardedField>,
22
23    pub container: Core,
24
25    /// The attribute names that should be searched.
26    pub attr_names: PathList,
27
28    /// The attribute names that should be forwarded. The presence of the word with no additional
29    /// filtering will cause _all_ attributes to be cloned and exposed to the struct after parsing.
30    pub forward_attrs: Option<ForwardAttrsFilter>,
31
32    /// Whether or not the container can be made through conversion from the type `Ident`.
33    pub from_ident: bool,
34}
35
36impl OuterFrom {
37    pub fn start(di: &syn::DeriveInput) -> Result<Self> {
38        Ok(OuterFrom {
39            container: Core::start(di)?,
40            attrs: Default::default(),
41            ident: Default::default(),
42            attr_names: Default::default(),
43            forward_attrs: Default::default(),
44            from_ident: Default::default(),
45        })
46    }
47
48    pub fn as_forward_attrs(&self) -> ForwardAttrs<'_> {
49        ForwardAttrs {
50            field: self.attrs.as_ref(),
51            filter: self.forward_attrs.as_ref(),
52        }
53    }
54}
55
56impl ParseAttribute for OuterFrom {
57    fn parse_nested(&mut self, mi: &Meta) -> Result<()> {
58        let path = mi.path();
59        if path.is_ident("attributes") {
60            self.attr_names = FromMeta::from_meta(mi)?;
61        } else if path.is_ident("forward_attrs") {
62            self.forward_attrs = FromMeta::from_meta(mi)?;
63        } else if path.is_ident("from_ident") {
64            // HACK: Declaring that a default is present will cause fields to
65            // generate correct code, but control flow isn't that obvious.
66            self.container.default = Some(DefaultExpression::Trait {
67                // Use the span of the `from_ident` keyword so that errors in generated code
68                // caused by this will point back to the correct location.
69                span: path.span(),
70            });
71            self.from_ident = true;
72        } else {
73            return self.container.parse_nested(mi);
74        }
75        Ok(())
76    }
77}
78
79impl ParseData for OuterFrom {
80    fn parse_field(&mut self, field: &Field) -> Result<()> {
81        match field.ident.as_ref().map(|v| v.to_string()).as_deref() {
82            Some("ident") => {
83                self.ident.clone_from(&field.ident);
84                Ok(())
85            }
86            Some("attrs") => {
87                self.attrs = ForwardedField::from_field(field).map(Some)?;
88                Ok(())
89            }
90            _ => self.container.parse_field(field),
91        }
92    }
93
94    fn validate_body(&self, errors: &mut crate::error::Accumulator) {
95        self.container.validate_body(errors);
96        if let Some(attrs) = &self.attrs {
97            if self.forward_attrs.is_none() {
98                let container_name = match &self.container.data {
99                    Data::Enum(_) => "enum",
100                    Data::Struct(_) => "struct",
101                };
102                errors.push(
103                    Error::custom(format!(
104                        "field will not be populated because `forward_attrs` is not set on the {}",
105                        container_name
106                    ))
107                    .with_span(&attrs.ident),
108                );
109            }
110        }
111
112        if let Some(ForwardAttrsFilter::Only(fwd)) = &self.forward_attrs {
113            for path in fwd.intersection(&self.attr_names) {
114                errors.push(
115                    Error::custom(format!(
116                        "attribute path `{}` will not be forwarded because it is also listed in `attributes`",
117                        path.to_token_stream()
118                    ))
119                    .with_span(path),
120                );
121            }
122        };
123    }
124}
darling_core/options/outer_from.rs

darling_core/options/
outer_from.rs
