Fix execution branch confusion with multiple variable assignments in if/else

- Changed createConditionalExpressions to create pairwise conditional holders instead of one holder with all guards
- In a binary branch merge, any single type guard uniquely identifies the branch, so individual guards are sufficient
- Previously, 3+ type guards created holders requiring all-minus-one conditions, causing circular dependency in resolution
- New regression test in tests/PHPStan/Analyser/nsrt/bug-5051.php

Closes phpstan/phpstan#5051

Author: phpstan-bot

src/Analyser/MutatingScope.php

@@ -4141,17 +4141,21 @@ private function createConditionalExpressions(
 				continue;
 			}
 
-			$conditionalExpression = new ConditionalExpressionHolder($variableTypeGuards, $holder);
-			$conditionalExpressions[$exprString][$conditionalExpression->getKey()] = $conditionalExpression;
+			foreach ($variableTypeGuards as $guardExprString => $guardHolder) {
+				$conditionalExpression = new ConditionalExpressionHolder([$guardExprString => $guardHolder], $holder);
+				$conditionalExpressions[$exprString][$conditionalExpression->getKey()] = $conditionalExpression;
+			}
 		}
 
 		foreach ($mergedExpressionTypes as $exprString => $mergedExprTypeHolder) {
 			if (array_key_exists($exprString, $ourExpressionTypes)) {
 				continue;
 			}
 
-			$conditionalExpression = new ConditionalExpressionHolder($typeGuards, new ExpressionTypeHolder($mergedExprTypeHolder->getExpr(), new ErrorType(), TrinaryLogic::createNo()));
-			$conditionalExpressions[$exprString][$conditionalExpression->getKey()] = $conditionalExpression;
+			foreach ($typeGuards as $guardExprString => $guardHolder) {
+				$conditionalExpression = new ConditionalExpressionHolder([$guardExprString => $guardHolder], new ExpressionTypeHolder($mergedExprTypeHolder->getExpr(), new ErrorType(), TrinaryLogic::createNo()));
+				$conditionalExpressions[$exprString][$conditionalExpression->getKey()] = $conditionalExpression;
+			}
 		}
 
 		return $conditionalExpressions;

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

@@ -0,0 +1,69 @@
+<?php declare(strict_types = 1);
+
+namespace Bug5051;
+
+use function PHPStan\Testing\assertType;
+
+class HelloWorld
+{
+	public function test(?object $data): void
+	{
+		if ($data === null) {
+			$foo = 'bar';
+			$update = false;
+		} else {
+			$foo = 'baz';
+			$update = true;
+		}
+
+		assertType('object|null', $data);
+		assertType("'bar'|'baz'", $foo);
+
+		if ($update) {
+			assertType('object', $data);
+		}
+	}
+
+	public function testWithBooleans(?object $data): void
+	{
+		if ($data === null) {
+			$update = false;
+			$foo = false;
+		} else {
+			$update = true;
+			$foo = true;
+		}
+
+		if ($update) {
+			assertType('object', $data);
+		}
+	}
+
+	public function testWithDifferentVariableNames(?object $data): void
+	{
+		if ($data === null) {
+			$update = false;
+			$foo = 'bar';
+		} else {
+			$update = true;
+			$fuu = 'baz';
+		}
+
+		if ($update) {
+			assertType('object', $data);
+		}
+	}
+
+	public function testWithoutExtraAssignment(?object $data): void
+	{
+		if ($data === null) {
+			$update = false;
+		} else {
+			$update = true;
+		}
+
+		if ($update) {
+			assertType('object', $data);
+		}
+	}
+}