Simplify if-else conditions to null coalesce / ternary

[HenkPoley]

New rule proposal: transforming simple if/else-based assignments into null coalesce operator.

Code example:

if (!isset($a)) {
    $b = $some_default;
} else {
    $b = $a;
}

Expected output:

$b = $a ?? $some_default;

Side note: It might also be clearer for single-line if-not-else statements to simply flip both arms and remove the not.

[SpacePossum]

Nice idea, we might even try a if-to-ternary rule, for example:

    if ($a) {
        $b = $some_default;
    } else {
        $b = $a;
    }

//

$b = $a ? $some_default : $a;

if we would run that one before TernaryToNullCoalescingFixer than your case would be fixed as well :)