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_meta_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 crate::ast::{Data, Fields, Style};
use crate::codegen::{Field, OuterFromImpl, TraitImpl, Variant};

pub struct FromMetaImpl<'a> {
    pub base: TraitImpl<'a>,
}

impl<'a> ToTokens for FromMetaImpl<'a> {
    fn to_tokens(&self, tokens: &mut TokenStream) {
        let base = &self.base;

        let impl_block = match base.data {
            // Unit structs allow empty bodies only.
            Data::Struct(ref vd) if vd.style.is_unit() => {
                let ty_ident = base.ident;
                quote!(
           
    
    fn to_tokens(&self, tokens: &mut TokenStream) {
        let base = &self.base;

        let impl_block = match base.data {
            // Unit structs allow empty bodies only.
            Data::Struct(ref vd) if vd.style.is_unit() => {
                let ty_ident = base.ident;
                quote!(
                    fn from_word() -> ::darling::Result<Self> {
                        ::darling::export::Ok(#ty_ident)
                    }
                )
            }

            // Newtype structs proxy to the sole value they contain.
            Data::Struct(Fields {
                ref fields,
                style: Style::Tuple,
                ..
            }) if fields.len() == 1 => {
                let ty_ident = base.ident;
                quote!(
                    fn from_meta(__item: &::darling::export::syn::Meta) -> ::darling::Result<Self> {
                        ::darling::FromMeta::from_meta(__item)
                            .map_err(|e| e.with_span(&__item))
                            .map(#ty_ident)
                    }
                )
            }
            Data::Struct(Fields {
                style: Style::Tuple,
                ..
            }) => {
                panic!("Multi-field tuples are not supported");
            }
            Data::Struct(ref data) => {
                let inits = data.fields.iter().map(Field::as_initializer);
                let declare_errors = base.declare_errors();
                let require_fields = base.require_fields();
                let check_errors = base.check_errors();
                let decls = base.local_declarations();
                let core_loop = base.core_loop();
                let default = base.fallback_decl();
                let post_transform = base.post_transform_call();

                quote!(
                    fn from_list(__items: &[::darling::export::NestedMeta]) -> ::darling::Result<Self> {

                        #decls

                        #declare_errors

                        #core_loop

                        #require_fields

                        #check_errors

                        #default

                        ::darling::export::Ok(Self {
                            #(#inits),*
                        }) #post_transform
                    }
                )
            }
            Data::Enum(ref variants) => {
                let unit_arms = variants.iter().map(Variant::as_unit_match_arm);

                let unknown_variant_err = if !variants.is_empty() {
                    let names = variants.iter().map(Variant::as_name);
                    quote! {
                        unknown_field_with_alts(__other, &[#(#names),*])
                    }
                } else {
                    quote! {
                        unknown_field(__other)
                    }
                };

                let word_or_err = variants
                    .iter()
                    .find_map(|variant| {
                        if variant.word {
                            let ty_ident = variant.ty_ident;
                            let variant_ident = variant.variant_ident;
                            Some(quote!(::darling::export::Ok(#ty_ident::#variant_ident)))
                        } else {
                            None
                        }
                    })
                    .unwrap_or_else(|| {
                        quote!(::darling::export::Err(
                            ::darling::Error::unsupported_format("word")
                        ))
                    });

                quote!(
                    fn from_list(__outer: &[::darling::export::NestedMeta]) -> ::darling::Result<Self> {
                        // An enum must have exactly one value inside the parentheses if it's not a unit
                        // match arm.
                        match __outer.len() {
                            0 => ::darling::export::Err(::darling::Error::too_few_items(1)),
                            1 => {
                                if let ::darling::export::NestedMeta::Meta(ref __nested) = __outer[0] {
                                    match ::darling::util::path_to_string(__nested.path()).as_ref() {
                                        #(#variants)*
                                        __other => ::darling::export::Err(::darling::Error::#unknown_variant_err.with_span(__nested))
                                    }
                                } else {
                                    ::darling::export::Err(::darling::Error::unsupported_format("literal"))
                                }
                            }
                            _ => ::darling::export::Err(::darling::Error::too_many_items(1)),
                        }
                    }

                    fn from_string(lit: &str) -> ::darling::Result<Self> {
                        match lit {
                            #(#unit_arms)*
                            __other => ::darling::export::Err(::darling::Error::unknown_value(__other))
                        }
                    }

                    fn from_word() -> ::darling::Result<Self> {
                        #word_or_err
                    }
                )
            }
        };

        self.wrap(impl_block, tokens);
    }