Fix phpstan/phpstan#13566: False positive staticMethod.impossibleType for conditional return type with void/never

- Fixed ImpossibleCheckTypeHelper to skip impossible check when rootExpr is a call argument in null (void) context
- The conditional return type ($exit is true ? never : void) describes behavioral control flow, not a type check
- Added regression test in tests/PHPStan/Rules/Comparison/data/bug-13566.php
- The root cause was that getConditionalSpecifiedTypes set rootExpr to the call argument via inner specifyTypesInCondition, causing findSpecifiedType to short-circuit with a false "always evaluates to false" result

Author: staabm

src/Rules/Comparison/ImpossibleCheckTypeHelper.php

@@ -252,7 +252,8 @@ public function findSpecifiedType(
 		}
 
 		$typeSpecifierScope = $this->treatPhpDocTypesAsCertain ? $scope : $scope->doNotTreatPhpDocTypesAsCertain();
-		$specifiedTypes = $this->typeSpecifier->specifyTypesInCondition($typeSpecifierScope, $node, $this->determineContext($typeSpecifierScope, $node));
+		$context = $this->determineContext($typeSpecifierScope, $node);
+		$specifiedTypes = $this->typeSpecifier->specifyTypesInCondition($typeSpecifierScope, $node, $context);
 
 		// don't validate types on overwrite
 		if ($specifiedTypes->shouldOverwrite()) {
@@ -268,6 +269,17 @@ public function findSpecifiedType(
 				return null;
 			}
 
+			// For void methods (null context), if the rootExpr is one of the call's arguments,
+			// the conditional return type describes behavioral control flow (e.g. void vs never
+			// based on a boolean flag), not a type check. Skip the impossible check.
+			if ($context->null() && $node instanceof Expr\CallLike) {
+				foreach ($node->getArgs() as $arg) {
+					if ($arg->value === $rootExpr) {
+						return null;
+					}
+				}
+			}
+
 			$rootExprType = ($this->treatPhpDocTypesAsCertain ? $scope->getType($rootExpr) : $scope->getNativeType($rootExpr));
 			if ($rootExprType instanceof ConstantBooleanType) {
 				return $rootExprType->getValue();

tests/PHPStan/Rules/Comparison/ImpossibleCheckTypeStaticMethodCallRuleTest.php

@@ -161,6 +161,12 @@ public function testBug12087b(): void
 		]);
 	}
 
+	public function testBug13566(): void
+	{
+		$this->treatPhpDocTypesAsCertain = true;
+		$this->analyse([__DIR__ . '/data/bug-13566.php'], []);
+	}
+
 	public static function getAdditionalConfigFiles(): array
 	{
 		return [

tests/PHPStan/Rules/Comparison/data/bug-13566.php

@@ -0,0 +1,23 @@
+<?php declare(strict_types = 1);
+
+namespace Bug13566;
+
+class HelloWorld
+{
+	/** @return ($exit is true ? never : void) */
+	public static function notFound(bool $exit = true): void
+	{
+		header('HTTP/1.1 404 Not Found', true, 404);
+
+		if ($exit) {
+			echo '404 Not Found';
+			exit;
+		}
+	}
+
+	public function test(): void
+	{
+		// send 404 header without exiting
+		self::notFound(false);
+	}
+}