darling_core\options/
core.rs

1use ident_case::RenameRule;
2
3use crate::ast::{Data, Fields, Style};
4use crate::codegen;
5use crate::codegen::PostfixTransform;
6use crate::error::Accumulator;
7use crate::options::{DefaultExpression, InputField, InputVariant, ParseAttribute, ParseData};
8use crate::{Error, FromMeta, Result};
9
10/// A struct or enum which should have `FromMeta` or `FromDeriveInput` implementations
11/// generated.
12#[derive(Debug, Clone)]
13pub struct Core {
14    /// The type identifier.
15    pub ident: syn::Ident,
16
17    /// The type's generics. If the type does not use any generics, this will
18    /// be an empty instance.
19    pub generics: syn::Generics,
20
21    /// Controls whether missing properties should cause errors or should be filled by
22    /// the result of a function call. This can be overridden at the field level.
23    pub default: Option<DefaultExpression>,
24
25    /// The rule that should be used to rename all fields/variants in the container.
26    pub rename_rule: RenameRule,
27
28    /// A transform which will be called on `darling::Result<Self>`. It must either be
29    /// an `FnOnce(T) -> T` when `map` is used, or `FnOnce(T) -> darling::Result<T>` when
30    /// `and_then` is used.
31    ///
32    /// `map` and `and_then` are mutually-exclusive to avoid confusion about the order in
33    /// which the two are applied.
34    pub post_transform: Option<codegen::PostfixTransform>,
35
36    /// The body of the _deriving_ type.
37    pub data: Data<InputVariant, InputField>,
38
39    /// The custom bound to apply to the generated impl
40    pub bound: Option<Vec<syn::WherePredicate>>,
41
42    /// Whether or not unknown fields should produce an error at compilation time.
43    pub allow_unknown_fields: Option<bool>,
44}
45
46impl Core {
47    /// Partially initializes `Core` by reading the identity, generics, and body shape.
48    pub fn start(di: &syn::DeriveInput) -> Result<Self> {
49        Ok(Core {
50            ident: di.ident.clone(),
51            generics: di.generics.clone(),
52            data: Data::try_empty_from(&di.data)?,
53            default: Default::default(),
54            // See https://github.com/TedDriggs/darling/issues/10: We default to snake_case
55            // for enums to help authors produce more idiomatic APIs.
56            rename_rule: if let syn::Data::Enum(_) = di.data {
57                RenameRule::SnakeCase
58            } else {
59                Default::default()
60            },
61            post_transform: Default::default(),
62            bound: Default::default(),
63            allow_unknown_fields: Default::default(),
64        })
65    }
66
67    fn as_codegen_default(&self) -> Option<codegen::DefaultExpression<'_>> {
68        self.default.as_ref().map(|expr| match *expr {
69            DefaultExpression::Explicit(ref path) => codegen::DefaultExpression::Explicit(path),
70            DefaultExpression::Inherit => {
71                // It should be impossible for any input to get here,
72                // so panic rather than returning an error or pretending
73                // everything is fine.
74                panic!("DefaultExpression::Inherit is not valid at container level")
75            }
76            DefaultExpression::Trait { span } => codegen::DefaultExpression::Trait { span },
77        })
78    }
79}
80
81impl ParseAttribute for Core {
82    fn parse_nested(&mut self, mi: &syn::Meta) -> Result<()> {
83        let path = mi.path();
84
85        if path.is_ident("default") {
86            if self.default.is_some() {
87                return Err(Error::duplicate_field("default").with_span(mi));
88            }
89
90            self.default = FromMeta::from_meta(mi)?;
91        } else if path.is_ident("rename_all") {
92            // WARNING: This may have been set based on body shape previously,
93            // so an overwrite may be permissible.
94            self.rename_rule = FromMeta::from_meta(mi)?;
95        } else if path.is_ident("map") || path.is_ident("and_then") {
96            // This unwrap is safe because we just called is_ident above
97            let transformer = path.get_ident().unwrap().clone();
98
99            if let Some(post_transform) = &self.post_transform {
100                if transformer == post_transform.transformer {
101                    return Err(Error::duplicate_field(&transformer.to_string()).with_span(mi));
102                } else {
103                    return Err(Error::custom(format!(
104                        "Options `{}` and `{}` are mutually exclusive",
105                        transformer, post_transform.transformer
106                    ))
107                    .with_span(mi));
108                }
109            }
110
111            self.post_transform =
112                Some(PostfixTransform::new(transformer, FromMeta::from_meta(mi)?));
113        } else if path.is_ident("bound") {
114            self.bound = FromMeta::from_meta(mi)?;
115        } else if path.is_ident("allow_unknown_fields") {
116            if self.allow_unknown_fields.is_some() {
117                return Err(Error::duplicate_field("allow_unknown_fields").with_span(mi));
118            }
119
120            self.allow_unknown_fields = FromMeta::from_meta(mi)?;
121        } else {
122            return Err(Error::unknown_field_path(path).with_span(mi));
123        }
124
125        Ok(())
126    }
127}
128
129impl ParseData for Core {
130    fn parse_variant(&mut self, variant: &syn::Variant) -> Result<()> {
131        let v = InputVariant::from_variant(variant, Some(self))?;
132
133        match self.data {
134            Data::Enum(ref mut variants) => {
135                variants.push(v);
136                Ok(())
137            }
138            Data::Struct(_) => panic!("Core::parse_variant should never be called for a struct"),
139        }
140    }
141
142    fn parse_field(&mut self, field: &syn::Field) -> Result<()> {
143        let f = InputField::from_field(field, Some(self))?;
144
145        match self.data {
146            Data::Struct(Fields {
147                style: Style::Unit, ..
148            }) => panic!("Core::parse_field should not be called on unit"),
149            Data::Struct(Fields { ref mut fields, .. }) => {
150                fields.push(f);
151                Ok(())
152            }
153            Data::Enum(_) => panic!("Core::parse_field should never be called for an enum"),
154        }
155    }
156
157    fn validate_body(&self, errors: &mut Accumulator) {
158        if let Data::Struct(fields) = &self.data {
159            let flatten_targets: Vec<_> = fields
160                .iter()
161                .filter_map(|field| {
162                    if field.flatten.is_present() {
163                        Some(field.flatten)
164                    } else {
165                        None
166                    }
167                })
168                .collect();
169
170            if flatten_targets.len() > 1 {
171                for flatten in flatten_targets {
172                    errors.push(
173                        Error::custom("`#[darling(flatten)]` can only be applied to one field")
174                            .with_span(&flatten.span()),
175                    );
176                }
177            }
178        }
179    }
180}
181
182impl<'a> From<&'a Core> for codegen::TraitImpl<'a> {
183    fn from(v: &'a Core) -> Self {
184        codegen::TraitImpl {
185            ident: &v.ident,
186            generics: &v.generics,
187            data: v
188                .data
189                .as_ref()
190                .map_struct_fields(InputField::as_codegen_field)
191                .map_enum_variants(|variant| variant.as_codegen_variant(&v.ident)),
192            default: v.as_codegen_default(),
193            post_transform: v.post_transform.as_ref(),
194            allow_unknown_fields: v.allow_unknown_fields.unwrap_or_default(),
195        }
196    }
197}
darling_core\options/core.rs

darling_core\options/
core.rs
