darling_core 0.23.0

Helper crate for proc-macro library for reading attributes into structs when implementing custom derives. Use https://crates.io/crates/darling in your code.
Documentation 
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use crate::{
    usage::{UsesLifetimes, UsesTypeParams},
    FromDeriveInput, FromField, FromGenericParam, FromGenerics, FromMeta, FromTypeParam,
    FromVariant, Result,
};

/// A container to parse some syntax and retain access to the original.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct WithOriginal<T, O> {
    pub parsed: T,
    pub original: O,
}

impl<T, O> WithOriginal<T, O> {
    pub fn new(parsed: T, original: O) -> Self {
        WithOriginal { parsed, original }
    }
}

macro_rules! with_original {
    ($trayt:ident, $func:ident, $syn:path) => {
        impl<T: $trayt> $trayt for WithOriginal<T, $syn> {
            fn $func(value: &$syn) -> Result<Self> {
                Ok(WithOriginal::new($trayt::$func(value)?, value.clone()))
            }
        }
    };
}

with_original!(FromDeriveInput, from_derive_input, syn::DeriveInput);
with_original!(FromField, from_field, syn::Field);
with_original!(FromGenerics, from_generics, syn::Generics);
with_original!(FromGenericParam, from_generic_param, syn::GenericParam);
with_original!(FromMeta, from_meta, syn::Meta);
with_original!(FromTypeParam, from_type_param, syn::TypeParam);
with_original!(FromVariant, from_variant, syn::Variant);

/// Get the lifetime usage of `parsed`.
impl<P: UsesLifetimes, O> UsesLifetimes for WithOriginal<P, O> {
    fn uses_lifetimes<'a>(
        &self,
        options: &crate::usage::Options,
        lifetimes: &'a crate::usage::LifetimeSet,
    ) -> crate::usage::LifetimeRefSet<'a> {
        self.parsed.uses_lifetimes(options, lifetimes)
    }
}

/// Get the type param usage of `parsed`.
impl<P: UsesTypeParams, O> UsesTypeParams for WithOriginal<P, O> {
    fn uses_type_params<'a>(
        &self,
        options: &crate::usage::Options,
        type_set: &'a crate::usage::IdentSet,
    ) -> crate::usage::IdentRefSet<'a> {
        self.parsed.uses_type_params(options, type_set)
    }
}