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: usage.rs
    path of file: ./repos/nickel/lsp/nls/src
    
    the code of the file until where you have to start completion: use std::collections::HashMap;

use nickel_lang_core::{
    environment::Environment as GenericEnvironment,
    identifier::Ident,
    position::RawSpan,
    term::{RichTerm, Term, Traverse, TraverseControl},
};

use crate::{field_walker::Def, identifier::LocIdent, pattern::Bindings};

pub type Environment = GenericEnvironment<Ident, Def>;

trait EnvExt {
    fn insert_def(&mut self, def: Def);
}

impl EnvExt for Environment {
    fn insert_def(&mut self, def: Def) {
        self.insert(def.ident().ident, def);
    }
}

/// A lookup table for finding variable usages and variable definitions.
///
/// Variable usages come from `Term::Var`, while variable definitions come
/// from `let` 
    
    fn pattern_path() {
        let (file, rt) = parse("let x@{ foo = a@{ bar = baz } } = 'Undefined in x + a + baz");
        let x0 = locced("x", file, 4..5);
        let x1 = locced("x", file, 48..49);
        let a0 = locced("a", file, 14..15);
        let a1 = locced("a", file, 52..53);
        let baz0 = locced("baz", file, 24..27);
        let baz1 = locced("baz", file, 56..59);
        let table = UsageLookup::new(&rt, &Environment::new());

        assert_eq!(
            table.usages(&x0.pos.unwrap()).cloned().collect::<Vec<_>>(),
            vec![x1]
        );
        assert_eq!(
            table.usages(&a0.pos.unwrap()).cloned().collect::<Vec<_>>(),
            vec![a1]
        );
        assert_eq!(
            table
                .usages(&baz0.pos.unwrap())
                .cloned()
                .collect::<Vec<_>>(),
            vec![baz1]
        );

        let x_def = table.def(&x1).unwrap();
        assert_eq!(x_def.ident(), x0);
        assert!(x_def.path().is_empty());

        let a_def = table.def(&a1).unwrap();
        assert_eq!(a_def.ident(), a0);
        assert_eq!(a_def.path(), &["foo".into()]);

        let baz_def = table.def(&baz1).unwrap();
        assert_eq!(baz_def.ident(), baz0);
        assert_eq!(baz_def.path(), vec!["foo".into(), "bar".into()]);
    }