Fix bug when specifying empty array

src/Analyser/TypeSpecifier.php

@@ -236,25 +236,36 @@ public function specifyTypesInCondition(
 				$exprLeftType = $scope->getType($expr->left);
 				$exprRightType = $scope->getType($expr->right);
 
+				$types = null;
+
 				if (
 					$exprLeftType instanceof ConstantType
-					&& !$exprRightType instanceof ConstantType
+					&& !$expr->right instanceof Node\Scalar
 				) {
-					return $this->create(
+					$types = $this->create(
 						$expr->right,
 						$exprLeftType,
 						$context
 					);
 				}
 				if (
 					$exprRightType instanceof ConstantType
-					&& !$exprLeftType instanceof ConstantType
+					&& !$expr->left instanceof Node\Scalar
 				) {
-					return $this->create(
+					$leftType = $this->create(
 						$expr->left,
 						$exprRightType,
 						$context
 					);
+					if ($types !== null) {
+						$types = $types->unionWith($leftType);
+					} else {
+						$types = $leftType;
+					}
+				}
+
+				if ($types !== null) {
+					return $types;
 				}
 			}
 

tests/PHPStan/Analyser/NodeScopeResolverTest.php

@@ -10530,6 +10530,11 @@ public function dataBug4206(): array
 		return $this->gatherAssertTypes(__DIR__ . '/data/bug-4206.php');
 	}
 
+	public function dataBugEmptyArray(): array
+	{
+		return $this->gatherAssertTypes(__DIR__ . '/data/bug-empty-array.php');
+	}
+
 	/**
 	 * @param string $file
 	 * @return array<string, mixed[]>
@@ -10721,6 +10726,7 @@ private function gatherAssertTypes(string $file): array
 	 * @dataProvider dataInferPrivateTypedPropertyTypeFromConstructor
 	 * @dataProvider dataBug4207
 	 * @dataProvider dataBug4206
+	 * @dataProvider dataBugEmptyArray
 	 * @param string $assertType
 	 * @param string $file
 	 * @param mixed ...$args

tests/PHPStan/Analyser/data/bug-empty-array.php

@@ -0,0 +1,43 @@
+<?php
+
+namespace EmptyArrayInProperty;
+
+use function PHPStan\Analyser\assertType;
+
+class Foo
+{
+
+	/** @var string[] */
+	private $comments;
+
+	public function doFoo(): void
+	{
+		assertType('array<string>', $this->comments);
+		$this->comments = [];
+		assertType('array()', $this->comments);
+		if ($this->comments === []) {
+			assertType('array()', $this->comments);
+			return;
+		} else {
+			assertType('*NEVER*', $this->comments);
+		}
+
+		assertType('*NEVER*', $this->comments);
+	}
+
+	public function doBar(): void
+	{
+		assertType('array<string>', $this->comments);
+		$this->comments = [];
+		assertType('array()', $this->comments);
+		if ([] === $this->comments) {
+			assertType('array()', $this->comments);
+			return;
+		} else {
+			assertType('*NEVER*', $this->comments);
+		}
+
+		assertType('*NEVER*', $this->comments);
+	}
+
+}