elseif.condNotBoolean - Phpstan

Code example

php

<?php declare(strict_types = 1);

function classify(string $value): string
{
    if ($value === 'admin') {
        return 'Administrator';
    } elseif ($value) { // error: Only booleans are allowed in an elseif condition, string given.
        return 'User';
    }

    return 'Guest';
}

This rule is provided by the package phpstan/phpstan-strict-rules.

Why is it reported?

PHP performs implicit type coercion when evaluating conditions. Values like 0, '', '0', [], and null are considered falsy. This implicit coercion can mask bugs -- for example, the string '0' is falsy, which may not be the intended behaviour.

Requiring explicit boolean expressions in elseif conditions makes the code's intent clearer and avoids subtle errors from truthy/falsy coercion.

How to fix it

Use an explicit comparison that returns a boolean:

diff-php

 <?php declare(strict_types = 1);

 function classify(string $value): string
 {
     if ($value === 'admin') {
         return 'Administrator';
-    } elseif ($value) {
+    } elseif ($value !== '') {
         return 'User';
     }

     return 'Guest';
 }