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use std::borrow::Cow;
use syn::{parse_quote_spanned, spanned::Spanned};
use crate::codegen;
use crate::options::{Core, DefaultExpression, ParseAttribute};
use crate::util::{Flag, SpannedValue};
use crate::{Error, FromMeta, Result};
#[derive(Debug, Clone)]
pub struct InputField {
pub ident: syn::Ident,
pub attr_name: Option<String>,
pub ty: syn::Type,
pub default: Option<DefaultExpression>,
pub with: Option<syn::Path>,
/// If `true`, generated code will not look for this field in the input meta item,
/// instead always falling back to either `InputField::default` or `Default::default`.
pub skip: Option<SpannedValue<bool>>,
pub post_transform: Option<codegen::PostfixTransform>,
pub multiple: Option<bool>,
pub flatten: Flag,
}
impl InputField {
/// Generate a view into this field that can be used for code generation.
pub fn as_codegen_field(&self) -> codegen::Field<'_> {
codegen::Field {
ident: &self.ident,
name_in_attr: self
.attr_name
.as_ref()
.map_or_else(|| Cow::Owned(self.ident.to_string()), Cow::Borrowed),
ty: &self.ty,
default_expression: self.as_codegen_default(),
with_path: self.with.as_ref().map_or_else(
|| {
Cow::Owned(
parse_quote_spanned!(self.ty.span()=> ::darling::FromMeta::from_meta),
)
},
Cow::Borrowed,
),
skip: *self.skip.unwrap_or_default(),
post_transform: self.post_transform.as_ref(),
multiple: self.multiple.unwrap_or_default(),
flatten: self.flatten.is_present(),
}
}
/// Generate a codegen::DefaultExpression for this field. This requires the field name
/// in the `Inherit` case.
fn as_codegen_default(&self) -> Option<codegen::DefaultExpression<'_>> {
self.default.as_ref().map(|expr| match *expr {
DefaultExpression::Explicit(ref path) => codegen::DefaultExpression::Explicit(path),
DefaultExpression::Inherit => codegen::DefaultExpression::Inherit(&self.ident),
DefaultExpression::Trait { span } => codegen::DefaultExpression::Trait { span },
})
}
fn new(ident: syn::Ident, ty: syn::Type) -> Self {
InputField {
ident,
ty,
attr_name: None,
default: None,
with: None,
skip: None,
post_transform: Default::default(),
multiple: None,
flatten: Default::default(),
}
}
pub fn from_field(f: &syn::Field, parent: Option<&Core>) -> Result<Self> {
let ident = f
.ident
.clone()
.unwrap_or_else(|| syn::Ident::new("__unnamed", ::proc_macro2::Span::call_site()));
let ty = f.ty.clone();
let base = Self::new(ident, ty).parse_attributes(&f.attrs)?;
Ok(if let Some(container) = parent {
base.with_inherited(container)
} else {
base
})
}
/// Apply inherited settings from the container. This is done _after_ parsing
/// to ensure deference to explicit field-level settings.
fn with_inherited(mut self, parent: &Core) -> Self {
// explicit renamings take precedence over rename rules on the container,
// but in the absence of an explicit name we apply the rule.
if self.attr_name.is_none() {
self.attr_name = Some(parent.rename_rule.apply_to_field(self.ident.to_string()));
}
// Determine the default expression for this field, based on three pieces of information:
// 1. Will we look for this field in the attribute?
// 1. Is there a locally-defined default?
// 1. Did the parent define a default?
self.default = match (&self.skip, self.default.is_some(), parent.default.is_some()) {
// If we have a default, use it.
(_, true, _) => self.default,
// If there isn't an explicit default but the struct sets a default, we'll
// inherit from that.
(_, false, true) => Some(DefaultExpression::Inherit),
// If we're skipping the field and no defaults have been expressed then we should
// use the ::darling::export::Default trait, and set the span to the skip keyword
// so that an error caused by the skipped field's type not implementing `Default`
// will correctly identify why darling is trying to use `Default`.
(Some(v), false, false) if **v => Some(DefaultExpression::Trait { span: v.span() }),
// If we don't have or need a default, then leave it blank.
(_, false, false) => None,
};
self
}
}
impl ParseAttribute for InputField {
fn parse_nested(&mut self, mi: &syn::Meta) -> Result<()> {
let path = mi.path();
if path.is_ident("rename") {
if self.attr_name.is_some() {
return Err(Error::duplicate_field_path(path).with_span(mi));
}
self.attr_name = FromMeta::from_meta(mi)?;
if self.flatten.is_present() {
return Err(
Error::custom("`flatten` and `rename` cannot be used together").with_span(mi),
);
}
} else if path.is_ident("default") {
if self.default.is_some() {
return Err(Error::duplicate_field_path(path).with_span(mi));
}
self.default = FromMeta::from_meta(mi)?;
} else if path.is_ident("with") {
if self.with.is_some() {
return Err(Error::duplicate_field_path(path).with_span(mi));
}
self.with = Some(FromMeta::from_meta(mi)?);
if self.flatten.is_present() {
return Err(
Error::custom("`flatten` and `with` cannot be used together").with_span(mi),
);
}
} else if path.is_ident("skip") {
if self.skip.is_some() {
return Err(Error::duplicate_field_path(path).with_span(mi));
}
self.skip = FromMeta::from_meta(mi)?;
if self.skip.map(|v| *v).unwrap_or_default() && self.flatten.is_present() {
return Err(
Error::custom("`flatten` and `skip` cannot be used together").with_span(mi),
);
}
} else if path.is_ident("map") || path.is_ident("and_then") {
let transformer = path.get_ident().unwrap().clone();
if let Some(post_transform) = &self.post_transform {
if transformer == post_transform.transformer {
return Err(Error::duplicate_field_path(path).with_span(mi));
} else {
return Err(Error::custom(format!(
"Options `{}` and `{}` are mutually exclusive",
transformer, post_transform.transformer
))
.with_span(mi));
}
}
self.post_transform = Some(codegen::PostfixTransform::new(
transformer,
FromMeta::from_meta(mi)?,
));
} else if path.is_ident("multiple") {
if self.multiple.is_some() {
return Err(Error::duplicate_field_path(path).with_span(mi));
}
self.multiple = FromMeta::from_meta(mi)?;
if self.multiple == Some(true) && self.flatten.is_present() {
return Err(
Error::custom("`flatten` and `multiple` cannot be used together").with_span(mi),
);
}
} else if path.is_ident("flatten") {
if self.flatten.is_present() {
return Err(Error::duplicate_field_path(path).with_span(mi));
}
self.flatten = FromMeta::from_meta(mi)?;
let mut conflicts = Error::accumulator();
if self.multiple == Some(true) {
conflicts.push(
Error::custom("`flatten` and `multiple` cannot be used together").with_span(mi),
);
}
if self.attr_name.is_some() {
conflicts.push(
Error::custom("`flatten` and `rename` cannot be used together").with_span(mi),
);
}
if self.with.is_some() {
conflicts.push(
Error::custom("`flatten` and `with` cannot be used together").with_span(mi),
);
}
if self.skip.map(|v| *v).unwrap_or_default() {
conflicts.push(
Error::custom("`flatten` and `skip` cannot be used together").with_span(mi),
);
}
conflicts.finish()?;
} else {
return Err(Error::unknown_field_path(path).with_span(mi));
}
Ok(())
}
}