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_variant_impl.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, ForwardAttrs, OuterFromImpl, TraitImpl};
use crate::options::DataShape;
use crate::util::PathList;

pub struct FromVariantImpl<'a> {
    pub base: TraitImpl<'a>,
    /// If set, the ident of the field into which the variant ident should be placed.
    ///
    /// This is one of `darling`'s "magic fields", which allow a type deriving a `darling`
    /// trait to get fields from the input `syn` element added to the deriving struct
    /// automatically.
    pub ident: Option<&'a Ident>,
    /// If set, the ident of the field into which the transformed output of the input
    /// variant's fields should be placed.
    ///
    /// This is one of `darling`'s "magic fields".
    pub fields: Option<&'a Ident>,
    /// If set, the ident of the field into which the discriminant of the input variant
    /// should be placed. The receiving field must be an `Option` as not all enums have
    /// discriminants.
    ///
    /// This is one of `darling`'s "magic fields".
    pub discriminant: Option<&'a Ident>,
    pub attr_names: &'a PathList,
    pub forward_attrs: ForwardAttrs<'a>,
    pub from_ident: bool,
    pub supports: Option<&'a DataShape>,
}

impl<'a> ToTokens for FromVariantImpl<'a> {
    fn to_tokens(&self, tokens: &mut TokenStream) {
        let input = self.param_name();
        let extractor = self.extractor();
        let passed_ident = self
            .ident
            .as_ref()
            .map(|i| quote!(#i: #input.ident.clone(),));
        let passed_discriminant = self
            .discriminant
            .as_ref()
            .map(|i| quote!(#i: #input.discriminant.as_ref().map(|(_, expr)| expr.clone()),));
        let passed_attrs 
    
    fn to_tokens(&self, tokens: &mut TokenStream) {
        let input = self.param_name();
        let extractor = self.extractor();
        let passed_ident = self
            .ident
            .as_ref()
            .map(|i| quote!(#i: #input.ident.clone(),));
        let passed_discriminant = self
            .discriminant
            .as_ref()
            .map(|i| quote!(#i: #input.discriminant.as_ref().map(|(_, expr)| expr.clone()),));
        let passed_attrs = self.forward_attrs.as_initializer();
        let passed_fields = self
            .fields
            .as_ref()
            .map(|i| quote!(#i: ::darling::ast::Fields::try_from(&#input.fields)?,));

        let inits = self.base.initializers();
        let post_transform = self.base.post_transform_call();

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

        let supports = self.supports.map(|i| {
            quote! {
                __errors.handle(#i.check(&#input.fields));
            }
        });

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

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

                    #extractor

                    #supports

                    #require_fields

                    #error_check

                    #default

                    ::darling::export::Ok(Self {
                        #passed_ident
                        #passed_discriminant
                        #passed_attrs
                        #passed_fields
                        #inits
                    }) #post_transform
                }
            ),
            tokens,
        );
    }