handle another type of collapsible if-statement

[Arc8ne]

fixes #812

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changelog: [collapsible_if]: handle another type of collapsible if-statement

[rustbot]

r? @dswij

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[Arc8ne]

r? @samueltardieu

This PR is an updated version of PR #15027.

[Arc8ne]

@samueltardieu Thanks for the review, I have implemented your suggested changes in my latest commit and was wondering if you could re-review it?

[samueltardieu]

The suggestion may be wrong when operators other than == or != are used. Please fix, and also add more complicated tests involving conditions with binary operators, including && and || operators.

[samueltardieu]

What about other binary operations? Right now, the following

    let a = 10;
    let b = 20;

    if a < 20 {
        if b < 30 {
            println!("Hello");
        }
    } else {
        println!("world!");
    }

will be transformed into the (non equivalent)

    if a != 20 || b < 30 {
        println!("Hello world!");
    }

You should look at the ! operator for Sugg and let it invert the operation, it might be beneficial.

[Arc8ne]

The suggestion may be wrong when operators other than == or != are used. Please fix, and also add more complicated tests involving conditions with binary operators, including && and || operators.

Thanks for the review, I'll work on implementing those suggestions.

[rustbot]

☔ The latest upstream changes (possibly #14896) made this pull request unmergeable. Please resolve the merge conflicts.