Spot useless nested if test conditions

[leonardo-m]

I'd like Clippy to spot situations like this, here the second "if" condition is useless:

fn foo7(x: u32) {
    if x == 5 {
        println!("A");
        if x == 5 {
            println!("B");
        }
    }
}

[mcarton]

Most of what you propose look a lot like abstract interpretation with octagonal domains. We don't do that yet, but it would be an interesting project.

[matthiaskrgr]

For a more advanced version of this, clippy should also notice thatif x.is_some() and if let Some(y) = x are basically the same

fn foo(o: Option<String>) {
    if o.is_some() {
        // some code
        if let Some(s) = o {  // same as previous cond
            // some more code
        }
    }
}