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: src.rs
    path of file: ./repos/mun/crates/mun_hir/src/code_model
    
    the code of the file until where you have to start completion: use mun_syntax::ast;

use crate::{
    code_model::{Field, Function, Struct, TypeAlias},
    ids::{AssocItemLoc, Lookup},
    in_file::InFile,
    item_tree::{ItemTreeId, ItemTreeNode},
    DefDatabase, ItemLoc
    
    fn source(&self, db: &dyn DefDatabase) -> InFile<Self::Ast> {
        let tree = db.item_tree(self.file_id);
        let ast_id_map = db.ast_id_map(self.file_id);
        let root = db.parse(self.file_id);
        let node = &tree[self.value];

        InFile::new(
            self.file_id,
            ast_id_map.get(node.ast_id()).to_node(&root.syntax_node()),
        )
    }