New lint: map_unwrap_or_bool

What it does

This lint discourages a less readable idiom when checking an operation which returns an Option<T> chained with a boolean predicate.

My main motivation is to avoid a bad habit of mine while I was still learning all the parts of the APIs. I imagine I am not the only one who learned it.

Categories

• Kind: clippy::pedantic

What is the advantage of the recommended code over the original code

• Makes the intention clearer
• Uses a function that is literally designed for this
• Allows additional access to the returned value, such as let Some(...) clauses

Drawbacks

Could be superseded by rust-lang/rust#75298

Example

fn main() {
    let https_proxy: Option<String> = std::env::var("HTTPS_PROXY").ok();

    if https_proxy.map(|v| v.starts_with("https://")).unwrap_or(false) {
        eprintln!("You have an HTTPS proxy set in the environment");
    } else {
        eprintln!("You do not have an HTTPS proxy set in the environment");
    }
}

Could be written as:

fn main() {
    let https_proxy: Option<String> = std::env::var("HTTPS_PROXY").ok();

    if https_proxy.filter(|v| v.starts_with("https://")).is_some() {
        eprintln!("You have an HTTPS proxy set in the environment");
    } else {
        eprintln!("You do not have an HTTPS proxy set in the environment");
    }
}

Begin by finding how existing Rust Clippy lints are registered and tested, then compare their handling of Option predicates with the issue's map(...).unwrap_or(false) example. Done means a clippy::pedantic lint named map_unwrap_or_bool recognizes the described idiom, suggests filter(...).is_some(), and covers the behavior with tests.