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: secret.rs
    path of file: ./repos/vector/src/config/loading
    
    the code of the file until where you have to start completion: use std::{
    collections::{HashMap, HashSet},
    io::Read,
};

use indexmap::IndexMap;
use once_cell::sync::Lazy;
use regex::{Captures, Regex};
use serde::{Deserialize, Serialize};
use toml::value::Table;
use vector_lib::config::ComponentKey;

use crate::{
    config::{
        loading::{deserialize_table, prepare_input, process::Process, ComponentHint, Loader},
        SecretBackend,
    },
    secrets::SecretBackends,
    signal,
};

// The following regex aims to extract a pair of
    
    fn replacement() {
        let secrets: HashMap<String, String> = vec![
            ("a.secret.key".into(), "value".into()),
            ("a...key".into(), "a...value".into()),
        ]
        .into_iter()
        .collect();

        assert_eq!(
            Ok("value".into()),
            interpolate("SECRET[a.secret.key]", &secrets)
        );
        assert_eq!(
            Ok("value value".into()),
            interpolate("SECRET[a.secret.key] SECRET[a.secret.key]", &secrets)
        );

        assert_eq!(
            Ok("xxxvalueyyy".into()),
            interpolate("xxxSECRET[a.secret.key]yyy", &secrets)
        );
        assert_eq!(
            Ok("a...value".into()),
            interpolate("SECRET[a...key]", &secrets)
        );
        assert_eq!(
            Ok("xxxSECRET[non_matching_syntax]yyy".into()),
            interpolate("xxxSECRET[non_matching_syntax]yyy", &secrets)
        );
        assert_eq!(
            Err(vec![
                "Unable to find secret replacement for SECRET[a.non.existing.key].".into()
            ]),
            interpolate("xxxSECRET[a.non.existing.key]yyy", &secrets)
        );
    }