PHP < 7.0: cannot use isset() on the result of an expression

[jrfnl]

Given the following code samples:

if (!isset(MY_CONSTANT[substr($data, 0, 2)])) {}

$marker = substr($data, 0, 2);
if (!isset(self::MY_CONSTANT[$marker])) {}

Linting this on PHP < 7.0 results in a Fatal error: Cannot use isset() on the result of an expression (you can use "null !== expression" instead) error.

Would be nice if we could detect this.

Patterns which do work cross-version:

$marker = substr($data, 0, 2);
if (!isset($array_var[$marker])) {
if (!isset(self::$array_var[$marker])) {
if (!isset($this->array_var[$marker])) {

I suspect this may be related to the Uniform Variable Syntax RFC, but haven't dug in to verify.

[villfa]

Here the RFC you're looking for: https://wiki.php.net/rfc/empty_isset_exprs

[jrfnl]

@villfa Unfortunately that's not the right RFC.

The RFC you referenced applies only to empty(). It was approved and merged into PHP 5.5 and is covered by the PHPCompatibility.LanguageConstructs.NewEmptyNonVariable sniff.

The change above is about isset() and the use of constants containing an array (as supported in PHP 5.6 and higher when declared using the const keyword).

[villfa]

My bad. I just notice the result of the vote excluded isset().

[jrfnl]

Just as a note for the record: running isset()on plain constants/class constants is fine, it's only array access on those constants which is problematic.

The ability to declare a const as an array was only added in PHP 5.6, the ability to do the same using define() was added in PHP 7.0, which is probably why the ability to use isset() on array access on constants was added in PHP 7.0.

Source: WordPress/wordpress-develop#3555 (comment)

Just ran into this one again. I still can't really find a relevant RFC, but I now think this is directly related to the addition of the ability to declare constant arrays in PHP. Doesn't look like either of those changes were handled via an RFC though, so finding the exact specs of the change will be sketchy.

Even so, I think a sniff which would detect isset() being used on array access on (class/global) constants should probably catch the most pertinent issues.