Fix phpstan/phpstan#12597: Variable might not be undefined after in_array check

When `in_array($type, [TYPE_1, TYPE_2], true)` narrows `$type` to a union
like `1|2` and a variable is assigned inside that block, a conditional
expression is created with guard type `1|2`. Later, when `$type === TYPE_1`
narrows to just `1`, the conditional didn't match because `equals()` requires
exact type equality.

Fix: In `filterBySpecifiedTypes`, allow conditional expression guards to match
when the specified type is a strict subtype of a finite union guard type. This
enables `$type = 1` to match the guard `$type = 1|2`, correctly resolving the
variable as defined.

The subtype matching is restricted to:
- Guards with >1 finite types (union of constants/literals)
- Both guard and specified having YES certainty
- The conditional's type holder having YES certainty (prevents matching stale
  "undefined" conditionals from earlier scope merges)
- Matches don't cascade (not added to specifiedExpressions) to prevent mutual
  conditional loops from corrupting type information

Author: staabm

src/Analyser/MutatingScope.php

@@ -3217,13 +3217,33 @@ public function filterBySpecifiedTypes(SpecifiedTypes $specifiedTypes): self
 					continue;
 				}
 				foreach ($conditionalExpressions as $conditionalExpression) {
+					$subtypeMatch = false;
 					foreach ($conditionalExpression->getConditionExpressionTypeHolders() as $holderExprString => $conditionalTypeHolder) {
-						if (!array_key_exists($holderExprString, $specifiedExpressions) || !$specifiedExpressions[$holderExprString]->equals($conditionalTypeHolder)) {
+						if (!array_key_exists($holderExprString, $specifiedExpressions)) {
 							continue 2;
 						}
+						$specifiedHolder = $specifiedExpressions[$holderExprString];
+						if ($specifiedHolder->equals($conditionalTypeHolder)) {
+							continue;
+						}
+						if (
+							$conditionalExpression->getTypeHolder()->getCertainty()->yes()
+							&& $specifiedHolder->getCertainty()->yes()
+							&& $conditionalTypeHolder->getCertainty()->yes()
+							&& count($conditionalTypeHolder->getType()->getFiniteTypes()) > 1
+							&& $conditionalTypeHolder->getType()->isSuperTypeOf($specifiedHolder->getType())->yes()
+						) {
+							$subtypeMatch = true;
+							continue;
+						}
+						continue 2;
 					}
 
 					$conditions[$conditionalExprString][] = $conditionalExpression;
+					if ($subtypeMatch) {
+						continue;
+					}
+
 					$specifiedExpressions[$conditionalExprString] = $conditionalExpression->getTypeHolder();
 				}
 			}

tests/PHPStan/Analyser/nsrt/bug-5051.php

@@ -60,35 +60,35 @@ public function testWithBooleans($data): void
 			assertType('bool', $update);
 		} else {
 			assertType('1|2', $data);
-			assertType('bool', $update);
+			assertType('false', $update);
 		}
 
 		if ($data === 1) {
-			assertType('bool', $update);
-			assertType('bool', $foo);
+			assertType('false', $update);
+			assertType('false', $foo);
 		} else {
 			assertType('bool', $update);
 			assertType('bool', $foo);
 		}
 
 		if ($data === 2) {
-			assertType('bool', $update);
-			assertType('bool', $foo);
+			assertType('false', $update);
+			assertType('false', $foo);
 		} else {
 			assertType('bool', $update);
 			assertType('bool', $foo);
 		}
 
 		if ($data === 3) {
-			assertType('bool', $update);
+			assertType('false', $update);
 			assertType('true', $foo);
 		} else {
 			assertType('bool', $update);
 			assertType('bool', $foo);
 		}
 
 		if ($data === 1 || $data === 2) {
-			assertType('bool', $update);
+			assertType('false', $update);
 			assertType('false', $foo);
 		} else {
 			assertType('bool', $update);

tests/PHPStan/Rules/Variables/DefinedVariableRuleTest.php

@@ -1476,6 +1476,15 @@ public function testBug14227(): void
 		$this->analyse([__DIR__ . '/data/bug-14227.php'], []);
 	}
 
+	public function testBug12597(): void
+	{
+		$this->cliArgumentsVariablesRegistered = true;
+		$this->polluteScopeWithLoopInitialAssignments = false;
+		$this->checkMaybeUndefinedVariables = true;
+		$this->polluteScopeWithAlwaysIterableForeach = true;
+		$this->analyse([__DIR__ . '/data/bug-12597.php'], []);
+	}
+
 	public function testBug14117(): void
 	{
 		$this->cliArgumentsVariablesRegistered = true;

tests/PHPStan/Rules/Variables/data/bug-12597.php

@@ -0,0 +1,22 @@
+<?php declare(strict_types = 1);
+
+namespace Bug12597;
+
+class HelloWorld
+{
+	private const TYPE_1 = 1;
+	private const TYPE_2 = 2;
+
+	public function test(int $type): void
+	{
+		if (in_array($type, [self::TYPE_1, self::TYPE_2], true)) {
+			$message = 'Hello!';
+		}
+
+		if ($type === self::TYPE_1) {
+			$this->message($message);
+		}
+	}
+
+	public function message(string $message): void {}
+}