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: mod.rs
    path of file: ./repos/vector/lib/vector-config-macros/src/ast
    
    the code of the file until where you have to start completion: use darling::{ast::NestedMeta, error::Accumulator, util::path_to_string, FromMeta};
use quote::ToTokens;
use serde_derive_internals::{ast as serde_ast, attr as serde_attr};

mod container;
mod field;
mod util;
mod variant;

pub use container::Container;
pub use field::Field;
use syn::Expr;
pub use variant::Variant;
use vector_config_common::constants;

const INVALID_VALUE_EXPR: &str =
    "got function call-style literal value but could not parse as expression";

///
    
    pub fn as_enum_metadata(&self) -> Vec<LazyCustomAttribute> {
        match self {
            Self::External => vec![LazyCustomAttribute::kv(
                constants::DOCS_META_ENUM_TAGGING,
                "external",
            )],
            Self::Internal { tag } => vec![
                LazyCustomAttribute::kv(constants::DOCS_META_ENUM_TAGGING, "internal"),
                LazyCustomAttribute::kv(constants::DOCS_META_ENUM_TAG_FIELD, tag),
            ],
            Self::Adjacent { tag, content } => vec![
                LazyCustomAttribute::kv(constants::DOCS_META_ENUM_TAGGING, "adjacent"),
                LazyCustomAttribute::kv(constants::DOCS_META_ENUM_TAG_FIELD, tag),
                LazyCustomAttribute::kv(constants::DOCS_META_ENUM_CONTENT_FIELD, content),
            ],
            Self::None => vec![LazyCustomAttribute::kv(
                constants::DOCS_META_ENUM_TAGGING,
                "untagged",
            )],
        }
    }