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: ddl.rs
    path of file: ./repos/materialize/src/sql-parser/src/ast/defs
    
    the code of the file until where you have to start completion: // Copyright 2018 sqlparser-rs contributors. All rights reserved.
// Copyright Materialize, Inc. and contributors. All rights reserved.
//
// This file is derived from the sqlparser-rs project, available at
// https://github.com/andygrove/sqlparser-rs. It was incorporated
// direct
    
fn display_constraint_name<'a>(name: &'a Option<Ident>) -> impl AstDisplay + 'a {
    struct ConstraintName<'a>(&'a Option<Ident>);
    impl<'a> AstDisplay for ConstraintName<'a> {
        fn fmt<W>(&self, f: &mut AstFormatter<W>)
        where
            W: fmt::Write,
        {
            if let Some(name) = self.0 {
                f.write_str("CONSTRAINT ");
                f.write_node(name);
                f.write_str(" ");
            }
        }
    }
    ConstraintName(name)
}