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: formatter.rs
    path of file: ./repos/charon/charon/src
    
    the code of the file until where you have to start completion: use crate::common::TAB_INCR;
use crate::gast;
use crate::llbc_ast;
use crate::llbc_ast::*;
use crate::types::*;
use crate::ullbc_ast;
use crate::ullbc_ast as ast;
use crate::values::*;

/// [`Formatter`](Formatter) is a trait for converting objects to string.
///
/// We need it 
    
    fn format_decl(&self, id: GlobalDeclId::Id) -> String {
        match &self.global_decls {
            None => format!("Unknown decl: {:?}", id),
            Some(decls) => match decls.get(id) {
                None => {
                    format!("Unknown decl: {:?}", id)
                }
                Some(d) => d.fmt_with_ctx(self),
            },
        }
    }