fix null coalesce false positive for multi-dimensional array in loop

Author: schlndh

src/Type/ArrayType.php

@@ -375,13 +375,33 @@ public function setOffsetValueType(?Type $offsetType, Type $valueType, bool $uni
 	public function setExistingOffsetValueType(Type $offsetType, Type $valueType): Type
 	{
 		if ($this->itemType->isConstantArray()->yes() && $valueType->isConstantArray()->yes()) {
-			$newItemType = $this->itemType;
+			$newItemTypes = [];
+
 			foreach ($valueType->getConstantArrays() as $constArray) {
-				foreach ($constArray->getKeyTypes() as $keyType) {
+				$newItemType = $this->itemType;
+				$optionalKeyTypes = [];
+				foreach ($constArray->getKeyTypes() as $i => $keyType) {
 					$newItemType = $newItemType->setExistingOffsetValueType($keyType, $constArray->getOffsetValueType($keyType));
+
+					if (!$constArray->isOptionalKey($i)) {
+						continue;
+					}
+
+					$optionalKeyTypes[] = $keyType;
+				}
+				$newItemTypes[] = $newItemType;
+
+				if ($optionalKeyTypes === []) {
+					continue;
+				}
+
+				foreach ($optionalKeyTypes as $keyType) {
+					$newItemType = $newItemType->unsetOffset($keyType);
 				}
+				$newItemTypes[] = $newItemType;
 			}
 
+			$newItemType = TypeCombinator::union(...$newItemTypes);
 			if ($newItemType !== $this->itemType) {
 				return new self(
 					$this->keyType,

tests/PHPStan/Analyser/AnalyserIntegrationTest.php

@@ -983,7 +983,7 @@ public function testBug7581(): void
 	public function testBug7903(): void
 	{
 		$errors = $this->runAnalyse(__DIR__ . '/data/bug-7903.php');
-		$this->assertCount(23, $errors);
+		$this->assertCount(24, $errors);
 	}
 
 	public function testBug7901(): void

tests/PHPStan/Rules/Variables/NullCoalesceRuleTest.php

@@ -337,6 +337,11 @@ public function testBug12553(): void
 		$this->analyse([__DIR__ . '/data/bug-12553.php'], []);
 	}
 
+	public function testBugMultiDimLoop(): void
+	{
+		$this->analyse([__DIR__ . '/data/bug-nullCoalesceMultiDimLoop.php'], []);
+	}
+
 	public function testIssetAfterRememberedConstructor(): void
 	{
 		$this->analyse([__DIR__ . '/data/isset-after-remembered-constructor.php'], [

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

@@ -0,0 +1,23 @@
+<?php declare(strict_types = 1);
+
+namespace BugNullCoalesceMultiDimLoop;
+
+/**
+ * @param array<int, array{1: int, 2: int, 3: float}> $rows
+ */
+function foo(array $rows): mixed
+{
+	$itemMap = [];
+
+	foreach ($rows as $row) {
+		$x = $row[1];
+		$month = $row[2];
+
+		$itemMap[$x][$month]['foo'] ??= 5;
+		$itemMap[$x][$month]['bar'] ??= 5;
+
+		$itemMap[$x][$month]['amount'] ??= 0.0;
+	}
+
+	return $itemMap;
+}