Sniff to flag is_a() and possibly replace with instanceof

[jrfnl]

Is your feature request related to a problem?

PHP has tried to deprecate the use of is_a() a couple of times already, so it is probably a good idea to have a sniff which can detect and (whenever possible) auto-fix any calls to is_a() with instanceof comparisons.

Additional reasons why this sniff would be a nice idea:

• Performance: using a PHP native operator will generally be faster than a function call, though it is a micro-optimization.
• IDE support: IDEs will be able to automatically fix/replace all uses of a class name when a class is renamed when the class name is used like a plain name and will, in most cases, not do so when a class name is in a text string.

Refs:

• https://www.php.net/manual/en/function.is-a.php
• https://www.php.net/manual/en/language.operators.type.php

Describe the solution you'd like

A new sniff in the Modernize standard.

Some example code:

// Bad.
if ( is_a( $var, 'MyClass' ) ) {}
if ( is_a( $var, MyClass::class ) ) {}
if ( is_a( $var, self::class ) ) {}

// Okay.
if ( $var instanceof \MyClass ) {}
if ( $var instanceof MyClass ) {} // If file is non-namespaced and/or there is an import `use` statement for the class.
if ( $var instanceof self ) {}

// Should probably be ignored by this sniff, or only flagged, but not auto-fixed ?
if ( is_a( $var, get_class( $obj ) ) ) {}
if ( is_a( $var, get_parent_class( $obj ) ) ) {}

Additional context (optional)

The sniff will need to take namespace/use statement resolution into account and be wary of creative code in the second parameter of the call to is_a() as it should be careful not to create bugs when auto-fixing.

Also note that since PHP 8.0 $obj::class is supported, so is_a( $var, $obj::class ) should be replaceable by ( $var instanceof $obj ).

Also be wary of the PHP 8.0 change that instanceof can then be used in arbitrary expressions, which means this wasn't allowed before and the auto-fixer should take this into account and be wary of this when auto-fixing.