[PROPOSAL] Disallow empty if and else blocks

[jlherren]

I'd like to propose a sniff that detects empty if and else blocks, since they never make any sense. Adding a comment inside the empty block would suppress the error, similar to DisallowEmptyFunctionSniff.

Empty elseif blocks can sometimes make sense if followed by other elseifs or an else.

Perhaps the sniff could even be fixable by extracting side-effects of the condition, however, it would be more useful if we can detect whether there are any side-effects at all, which I'm not sure is possible in phpcs.

[jlherren]

Oops, I meant to post this to slevomat/coding-standard, disregard that, sorry :(

[jrfnl]

@jlherren Just so you know, the Generic.CodeAnalysis.EmptyStatement would largely fit your needs. Could possibly do with some fine-tuning, in which case, I suspect a PR would be welcome.

if ($true) {
} elseif($bar) {
} else {
    // Do something.
}

--------------------------------------------------------------------------------------------------
FOUND 3 ERRORS AFFECTING 3 LINES
--------------------------------------------------------------------------------------------------
 3 | ERROR | Empty IF statement detected (Generic.CodeAnalysis.EmptyStatement.DetectedIf)
 4 | ERROR | Empty ELSEIF statement detected
   |       | (Generic.CodeAnalysis.EmptyStatement.DetectedElseif)
 5 | ERROR | Empty ELSE statement detected (Generic.CodeAnalysis.EmptyStatement.DetectedElse)
--------------------------------------------------------------------------------------------------

[jlherren]

Thanks for the hint. I always find it somewhat hard to discover what sniffs already exists. I've created #3409 to improve it.