{"ast_node_type":"variable","tokens":[{"end":79,"kind":"keyword","start":0,"text":"let"}]}
    let filler = &mut Filler { db, subst: &subst, trait_env, generics, owner };
    let generics = owner.as_generic_def_id(db).map(|g_def| generics(db, g_def));
    filler.fill_body(&mut body)?;