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: uniquify.rs
    path of file: ./repos/weld/weld/src/ast
    
    the code of the file until where you have to start completion: //! Defines the `Uniquify` trait on expressions.
//!
//! This trait makes symbol names unique in the AST.

use super::ast::ExprKind::*;
use super::ast
    
    fn symbol(&mut self, sym: Symbol) -> WeldResult<Symbol> {
        match self.stack.entry(sym.clone()) {
            Entry::Occupied(ref ent) => {
                let name = ent.key().name();
                let id = ent.get().last().cloned().ok_or_else(|| {
                    WeldCompileError::new(format!("Symbol {} is out of scope", &sym))
                })?;
                Ok(Symbol::new(name, id))
            }
            _ => compile_err!("Undefined symbol {}", sym),
        }
    }