Fix false positives on existing-offsets after assign

Author: staabm

src/Analyser/NodeScopeResolver.php

@@ -5480,8 +5480,7 @@ private function processAssignVar(
 				}
 
 				if ($originalVar->dim instanceof Variable || $originalVar->dim instanceof Node\Scalar) {
-					$currentVarType = $scope->getType($originalVar);
-					if (!$originalValueToWrite->isSuperTypeOf($currentVarType)->yes()) {
+					if (!$scope->hasExpressionType($originalVar)->yes()) {
 						$scope = $scope->assignExpression(
 							$originalVar,
 							$originalValueToWrite,

tests/PHPStan/Rules/Arrays/NonexistentOffsetInArrayDimFetchRuleTest.php

@@ -849,6 +849,13 @@ public function testArrayDimFetchOnArrayKeyFirsOrLastOrCount(): void
 		]);
 	}
 
+	public function testBug12406(): void
+	{
+		$this->reportPossiblyNonexistentGeneralArrayOffset = true;
+
+		$this->analyse([__DIR__ . '/data/bug-12406.php'], []);
+	}
+
 	public function testBug8649(): void
 	{
 		$this->reportPossiblyNonexistentGeneralArrayOffset = true;

tests/PHPStan/Rules/Arrays/data/bug-12406.php

@@ -0,0 +1,15 @@
+<?php
+
+namespace Bug12406;
+
+final class HelloWorld
+{
+	/** @var array<string, int> */
+	protected array $words = [];
+
+	public function sayHello(string $word, int $count): void
+	{
+		$this->words[$word] ??= 0;
+		$this->words[$word] += $count;
+	}
+}