use error_chain::{error_chain, error_chain_processing, impl_error_chain_kind, impl_error_chain_processed, impl_extract_backtrace}; error_chain! { errors { UnknownMigrationExists(v: String) { display("unknown migration version: '{}'", v), } } foreign_links { R2D2(::r2d2::Error); Migrations(::diesel_migrations::RunMigrationsError); Diesel(::diesel::result::Error); Connection(::diesel::ConnectionError); Io(::std::io::Error); } }