Fix phpstan/phpstan#12597: 'Variable might not be undefined' in if-statement after in_array check.

[phpstan-bot]

Summary

Fixes a false positive "Variable $message might not be defined" when a variable is assigned inside an in_array() check and later used inside a more specific condition (e.g., $type === self::TYPE_1) that implies the in_array() check was true.

Changes

• Added a second pass for conditional expression matching in src/Analyser/MutatingScope.php (~line 3232) that uses isSuperTypeOf() instead of equals() for type comparison
• The second pass is restricted to: targets that are Variables, have Maybe certainty (not-yet-definitely-defined), and are not already matched by the exact-match first pass
• Added regression test data in tests/PHPStan/Rules/Variables/data/bug-12597.php
• Added test method testBug12597() in tests/PHPStan/Rules/Variables/DefinedVariableRuleTest.php

Root cause

During scope merging after an if-without-else, PHPStan correctly creates conditional expressions like "if $type is 1|2, then $message is defined with Yes certainty." However, when later processing $type === 1, the specified type for $type is 1, which is a strict subtype of 1|2. The existing condition matching used ExpressionTypeHolder::equals() which requires exact type equality, so the conditional expression never matched. The fix adds a second pass after exact matching that uses isSuperTypeOf() for subtype checking, but only for variable targets with Maybe certainty to avoid interfering with type narrowing of already-defined expressions.

Test

The regression test reproduces the exact scenario from the issue: a variable assigned inside in_array($type, [TYPE_1, TYPE_2], true) and used inside $type === TYPE_1. The test expects no errors.

Fixes phpstan/phpstan#12597

[VincentLanglet]

Add non regression test

class HelloWorld
{
	public function test(mixed $type): void
	{
		if (is_int($type) || is_string($type)) {
			$message = 'Hello!';
		}

		if (is_int($type)) {
			$this->message($message);
		}
	}

	public function message(string $message): void {}
}

class Foo {}
class Bar {}

class HelloWorld2
{
	public function test(mixed $type): void
	{
		if (is_int($type) || is_object($type)) {
			$message = 'Hello!';
		}

		if (is_int($type)) {
			$this->message($message);
		}
	}

	public function test2(mixed $type): void
	{
		if ($type instanceof Foo || $type instanceof Bar) {
			$message = 'Hello!';
		}

		if ($type instanceof Foo) {
			$this->message($message);
		}
	}

	public function message(string $message): void
	{
	}
}

in DefinedVariableRuleTest.php‎

And update the implementation if necessary

[phpstan-bot]

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