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: builtin.rs
    path of file: ./repos/swc/crates/swc_ecma_preset_env/src/corejs3
    
    the code of the file until where you have to start completion: use once_cell::sync::Lazy;

use crate::util::{descriptor, CoreJSPolyfillDescriptor, ObjectMap, ObjectMap2};

fn dynamic_concat(a: &[&'static str], b: &[&'static str]) -> &'sta
    
fn dynamic_concat(a: &[&'static str], b: &[&'static str]) -> &'static [&'static str] {
    let mut res = Vec::with_capacity(a.len() + b.len());

    res.extend_from_slice(a);
    res.extend_from_slice(b);

    res.leak()
}