Drop unstable `Option::contains`, `Result::contains`, `Result::contains_err` This is a proposal to drop the three functions `Option::contains`, `Result::contains` and `Result::contains_err`. The discovery of `Option::is_some_with`/`Result::is_ok_with`/`Result::is_err_with` in https://github.com/rust-lang/rust/pull/93051 obviates the need for these methods (non-stabilization tracked in https://github.com/rust-lang/rust/issues/62358). An additional benefit of change is that it avoids spurious error messages in IDEs, when `contains` is supplied by a third-party library: