Fix phpstan/phpstan#14369: Null coalescing assignment operator combined with throwing (#5297)

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: phpstan-bot

src/Analyser/ExprHandler/AssignOpHandler.php

@@ -66,10 +66,11 @@ static function (MutatingScope $scope) use ($stmt, $expr, $nodeCallback, $contex
 				$exprResult = $nodeScopeResolver->processExprNode($stmt, $expr->expr, $scope, $storage, $nodeCallback, $context->enterDeep());
 				if ($expr instanceof Expr\AssignOp\Coalesce) {
 					$nodeScopeResolver->storeBeforeScope($storage, $expr, $originalScope);
+					$isAlwaysTerminating = $exprResult->isAlwaysTerminating() && $originalScope->getType($expr->var)->isNull()->yes();
 					return new ExpressionResult(
 						$exprResult->getScope()->mergeWith($originalScope),
 						$exprResult->hasYield(),
-						$exprResult->isAlwaysTerminating(),
+						$isAlwaysTerminating,
 						$exprResult->getThrowPoints(),
 						$exprResult->getImpurePoints(),
 					);

tests/PHPStan/Analyser/nsrt/bug-14369.php

@@ -0,0 +1,35 @@
+<?php // lint >= 8.0
+
+declare(strict_types = 1);
+
+namespace Bug14369;
+
+use Exception;
+use function PHPStan\Testing\assertType;
+
+function test(string|null $test): void
+{
+	$test ??= throw new Exception();
+
+	assertType('string', $test);
+}
+
+function testMaybeNull(): void
+{
+	if (rand(0, 1)) {
+		$test = null;
+	} else {
+		$test = 'hello';
+	}
+	$test ??= throw new Exception();
+
+	assertType("'hello'", $test);
+}
+
+function testAlwaysNull(): void
+{
+	$test = null;
+	$test ??= throw new Exception();
+
+	assertType('*NEVER*', $test);
+}

tests/PHPStan/Rules/DeadCode/UnreachableStatementRuleTest.php

@@ -397,4 +397,19 @@ public function testBug14328(): void
 		]);
 	}
 
+	public function testBug14369(): void
+	{
+		$this->treatPhpDocTypesAsCertain = true;
+		$this->analyse([__DIR__ . '/data/bug-14369.php'], [
+			[
+				'Unreachable statement - code above always terminates.',
+				33,
+			],
+			[
+				'Unreachable statement - code above always terminates.',
+				40,
+			],
+		]);
+	}
+
 }

tests/PHPStan/Rules/DeadCode/data/bug-14369.php

@@ -0,0 +1,47 @@
+<?php // lint >= 8.0
+
+declare(strict_types = 1);
+
+namespace Bug14369DeadCode;
+
+use Exception;
+
+function test(string|null $test): void
+{
+	$test ??= throw new Exception();
+
+	echo $test;
+}
+
+function testMaybeNull(): void
+{
+	if (rand(0, 1)) {
+		$test = null;
+	} else {
+		$test = 'hello';
+	}
+	$test ??= throw new Exception();
+
+	echo $test;
+}
+
+function testAlwaysNull(): void
+{
+	$test = null;
+	$test ??= throw new Exception();
+
+	echo $test;
+}
+
+function testAlwaysTerminatingLhs(): void
+{
+	alwaysThrows()->prop ??= throw new Exception();
+
+	echo 'unreachable';
+}
+
+/** @return never */
+function alwaysThrows(): never
+{
+	throw new Exception();
+}