Fix phpstan/phpstan#13669: Offset -1|0|1|2 might not exist on non-empty-array<-1|0|1|2, int>.

src/Analyser/ExprHandler/AssignHandler.php

@@ -948,7 +948,8 @@
 
 		$offsetValueTypeStack = [$offsetValueType];
 		$generalizeOnWrite = $offsetTypes[array_key_last($offsetTypes)][0] !== null;
-		foreach (array_slice($offsetTypes, 0, -1) as [$offsetType, $dimFetch]) {
+		$slicedOffsets = array_slice($offsetTypes, 0, -1);
+		foreach ($slicedOffsets as $k => [$offsetType, $dimFetch]) {
 			if ($offsetType === null) {
 				$offsetValueType = new ConstantArrayType([], []);
 				$generalizeOnWrite = false;
@@ -959,7 +960,13 @@
 				} elseif ($has->maybe()) {
 					if ($scope->hasExpressionType($dimFetch)->yes()) {
 						$generalizeOnWrite = false;
-						$offsetValueType = $offsetValueType->getOffsetValueType($offsetType);
+						$scopeType = $scope->getType($dimFetch);
+						$nextOffsetType = $offsetTypes[$k + 1][0] ?? null;
+						if ($nextOffsetType !== null && $scopeType->hasOffsetValueType($nextOffsetType)->yes()) {
+							$offsetValueType = $scopeType;
+						} else {
+							$offsetValueType = $offsetValueType->getOffsetValueType($offsetType);
+						}
 					} else {
 						$offsetValueType = TypeCombinator::union($offsetValueType->getOffsetValueType($offsetType), new ConstantArrayType([], []));
 					}

src/Analyser/MutatingScope.php

@@ -3852,6 +3852,18 @@
 					continue;
 				}
 
+				if (isset($otherVariableTypeHolders[$variableExprString])) {
+					$thisType = $variableTypeHolder->getType();
+					$otherType = $otherVariableTypeHolders[$variableExprString]->getType();
+					if (
+						$thisType->isConstantArray()->yes()
+						&& $otherType->isConstantArray()->yes()
+						&& $thisType->getIterableKeyType()->equals($otherType->getIterableKeyType())
+					) {
+						break;
+					}
+				}
+
 				continue 2;
 			}
 			if (!isset($otherVariableTypeHolders[$variableExprString])) {

tests/PHPStan/Rules/Arrays/NonexistentOffsetInArrayDimFetchRuleTest.php

@@ -1263,4 +1263,11 @@ public function testBug14308(): void
 		$this->analyse([__DIR__ . '/data/bug-14308.php'], []);
 	}
 
+	public function testBug13669(): void
+	{
+		$this->reportPossiblyNonexistentGeneralArrayOffset = true;
+
+		$this->analyse([__DIR__ . '/data/bug-13669.php'], []);
+	}
+
 }

tests/PHPStan/Rules/Arrays/data/bug-13669.php

@@ -0,0 +1,48 @@
+<?php declare(strict_types = 1);
+
+namespace Bug13669;
+
+final class Foo
+{
+	/**
+	 * @var array<int, array<MailStatus::CODE_*, int>>
+	 */
+	private array $mailCounts;
+
+	/** @var array<int, array<MailStatus::CODE_*>> */
+	private array $sources;
+
+	/** @param array<int, array<MailStatus::CODE_*>> $sources */
+	private function __construct(array $sources)
+	{
+		$this->mailCounts = [];
+		$this->sources = $sources;
+	}
+
+	public function countMailStates(): void
+	{
+		foreach ($this->sources as $templateId => $mails) {
+			$this->mailCounts[$templateId] = [
+				MailStatus::CODE_DELETED => 0,
+				MailStatus::CODE_NOT_ACTIVE => 0,
+				MailStatus::CODE_ACTIVE => 0,
+				MailStatus::CODE_SIMULATION => 0,
+			];
+
+			foreach ($mails as $mail) {
+				++$this->mailCounts[$templateId][$mail];
+			}
+		}
+	}
+}
+
+final class MailStatus
+{
+	public const CODE_DELETED = -1;
+
+	public const CODE_NOT_ACTIVE = 0;
+
+	public const CODE_SIMULATION = 1;
+
+	public const CODE_ACTIVE = 2;
+}