You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: from_field.rs
    path of file: ./repos/darling/core/src/codegen
    
    the code of the file until where you have to start completion: use proc_macro2::TokenStream;
use quote::{quote, ToTokens};
use syn::Ident;

use crate::{
    codegen::{ExtractAttribute, OuterFromImpl, TraitImpl},
    util::PathList,
};

use super::ForwardAttrs;

/// `impl FromField` generator. This is used for parsing an individual
/// field and its attributes.
pub struct FromFieldImpl<'a> {
    pub ident: Option<&'a Ident>,
    pub vis: Option<&'a Ident>,
    pub ty: Option<&'a Ident>,
    pub base: TraitImpl<'a
    
    fn to_tokens(&self, tokens: &mut TokenStream) {
        let input = self.param_name();

        let error_declaration = self.base.declare_errors();
        let require_fields = self.base.require_fields();
        let error_check = self.base.check_errors();

        let initializers = self.base.initializers();

        let default = if self.from_ident {
            quote!(let __default: Self = ::darling::export::From::from(#input.ident.clone());)
        } else {
            self.base.fallback_decl()
        };

        let passed_ident = self
            .ident
            .as_ref()
            .map(|i| quote!(#i: #input.ident.clone(),));
        let passed_vis = self.vis.as_ref().map(|i| quote!(#i: #input.vis.clone(),));
        let passed_ty = self.ty.as_ref().map(|i| quote!(#i: #input.ty.clone(),));
        let passed_attrs = self.forward_attrs.as_initializer();

        // Determine which attributes to forward (if any).
        let grab_attrs = self.extractor();
        let post_transform = self.base.post_transform_call();

        self.wrap(
            quote! {
                fn from_field(#input: &::darling::export::syn::Field) -> ::darling::Result<Self> {
                    #error_declaration

                    #grab_attrs

                    #require_fields

                    #error_check

                    #default

                    ::darling::export::Ok(Self {
                        #passed_ident
                        #passed_ty
                        #passed_vis
                        #passed_attrs
                        #initializers
                    }) #post_transform

                }
            },
            tokens,
        );
    }