Do not report non existent offset when it s an array creation

src/Analyser/NodeScopeResolver.php

@@ -5628,10 +5628,9 @@ private function processAssignVar(
 			$varNativeType = $scope->getNativeType($var);
 
 			// 4. compose types
-			if ($varType instanceof ErrorType) {
+			$isImplicitArrayCreation = $this->isImplicitArrayCreation($dimFetchStack, $scope);
+			if ($isImplicitArrayCreation->yes()) {
 				$varType = new ConstantArrayType([], []);
-			}
-			if ($varNativeType instanceof ErrorType) {
 				$varNativeType = new ConstantArrayType([], []);
 			}
 			$offsetValueType = $varType;
@@ -6018,6 +6017,27 @@ static function (): void {
 		return new ExpressionResult($scope, $hasYield, $isAlwaysTerminating, $throwPoints, $impurePoints);
 	}
 
+	/**
+	 * @param list<ArrayDimFetch> $dimFetchStack
+	 */
+	private function isImplicitArrayCreation(array $dimFetchStack, Scope $scope): TrinaryLogic
+	{
+		if (count($dimFetchStack) === 0) {
+			return TrinaryLogic::createNo();
+		}
+
+		$varNode = $dimFetchStack[0]->var;
+		if (!$varNode instanceof Variable) {
+			return TrinaryLogic::createNo();
+		}
+
+		if (!is_string($varNode->name)) {
+			return TrinaryLogic::createNo();
+		}
+
+		return $scope->hasVariableType($varNode->name)->negate();
+	}
+
 	/**
 	 * @param list<ArrayDimFetch> $dimFetchStack
 	 * @param list<Type|null> $offsetTypes

src/Rules/Arrays/NonexistentOffsetInArrayDimFetchRule.php

@@ -3,6 +3,8 @@
 namespace PHPStan\Rules\Arrays;
 
 use PhpParser\Node;
+use PhpParser\Node\Expr\ArrayDimFetch;
+use PhpParser\Node\Expr\Variable;
 use PHPStan\Analyser\NullsafeOperatorHelper;
 use PHPStan\Analyser\Scope;
 use PHPStan\DependencyInjection\AutowiredParameter;
@@ -11,6 +13,7 @@
 use PHPStan\Rules\Rule;
 use PHPStan\Rules\RuleErrorBuilder;
 use PHPStan\Rules\RuleLevelHelper;
+use PHPStan\TrinaryLogic;
 use PHPStan\Type\ErrorType;
 use PHPStan\Type\Type;
 use PHPStan\Type\VerbosityLevel;
@@ -42,6 +45,10 @@ public function getNodeType(): string
 
 	public function processNode(Node $node, Scope $scope): array
 	{
+		if ($this->isImplicitArrayCreation($node, $scope)->yes()) {
+			return [];
+		}
+
 		if ($node->dim !== null) {
 			$dimType = $scope->getType($node->dim);
 			$unknownClassPattern = sprintf('Access to offset %s on an unknown class %%s.', SprintfHelper::escapeFormatString($dimType->describe(VerbosityLevel::value())));
@@ -153,4 +160,22 @@ public function processNode(Node $node, Scope $scope): array
 		);
 	}
 
+	private function isImplicitArrayCreation(Node\Expr\ArrayDimFetch $node, Scope $scope): TrinaryLogic
+	{
+		$varNode = $node->var;
+		while ($varNode instanceof ArrayDimFetch) {
+			$varNode = $varNode->var;
+		}
+
+		if (!$varNode instanceof Variable) {
+			return TrinaryLogic::createNo();
+		}
+
+		if (!is_string($varNode->name)) {
+			return TrinaryLogic::createNo();
+		}
+
+		return $scope->hasVariableType($varNode->name)->negate();
+	}
+
 }

tests/PHPStan/Analyser/nsrt/bug-12447-bis.php

@@ -0,0 +1,22 @@
+<?php declare(strict_types = 1);
+
+namespace Bug12447Bis;
+
+use function PHPStan\Testing\assertType;
+
+interface Foo
+{
+
+}
+
+class HelloWorld
+{
+
+	public function __invoke(Foo $foo): void
+	{
+		$a = $foo->doFoo();
+		assertType('*ERROR*', $a);
+		$a[] = 5;
+		assertType('mixed', $a);
+	}
+}

tests/PHPStan/Analyser/nsrt/bug-12447.php

@@ -0,0 +1,15 @@
+<?php declare(strict_types = 1);
+
+namespace Bug12447;
+
+use function PHPStan\Testing\assertType;
+
+assertType('mixed', $data);
+$data[] = 1;
+assertType('mixed', $data);
+
+function (): void {
+	assertType('*ERROR*', $data);
+	$data[] = 1;
+	assertType('array{1}', $data);
+};

tests/PHPStan/Rules/Arrays/NonexistentOffsetInArrayDimFetchRuleTest.php

@@ -926,4 +926,17 @@ public function testBug3747(): void
 		$this->analyse([__DIR__ . '/data/bug-3747.php'], []);
 	}
 
+	public function testBug12447(): void
+	{
+		$this->checkExplicitMixed = true;
+		$this->checkImplicitMixed = true;
+
+		$this->analyse([__DIR__ . '/data/bug-12447.php'], [
+			[
+				'Cannot access an offset on mixed.',
+				5,
+			],
+		]);
+	}
+
 }

tests/PHPStan/Rules/Arrays/data/bug-12447.php

@@ -0,0 +1,9 @@
+<?php declare(strict_types = 1);
+
+namespace Bug12447;
+
+$data[] = 1;
+
+function (): void {
+	$data[] = 1;
+};

tests/PHPStan/Rules/Comparison/StrictComparisonOfDifferentTypesRuleTest.php

@@ -986,6 +986,11 @@ public function testBug12748(): void
 		$this->analyse([__DIR__ . '/data/bug-12748.php'], []);
 	}
 
+	public function testBug3803(): void
+	{
+		$this->analyse([__DIR__ . '/data/bug-3803.php'], []);
+	}
+
 	public function testBug11019(): void
 	{
 		$this->analyse([__DIR__ . '/data/bug-11019.php'], []);

tests/PHPStan/Rules/Comparison/data/bug-3803.php

@@ -0,0 +1,16 @@
+<?php declare(strict_types = 1);
+
+namespace Bug3803;
+
+/** @param array<string> $chars */
+function fun(array $chars) : void{
+	$string = "";
+	foreach($chars as $k => $v){
+		$string[$k] = $v;
+	}
+	if($string === "wheee"){
+		var_dump("yes");
+	}
+}
+
+fun(["w", "h", "e", "e", "e"]);

tests/PHPStan/Rules/Variables/UnsetRuleTest.php

@@ -65,6 +65,11 @@ public function testBug4289(): void
 		$this->analyse([__DIR__ . '/data/bug-4289.php'], []);
 	}
 
+	public function testBug4204(): void
+	{
+		$this->analyse([__DIR__ . '/data/bug-4204.php'], []);
+	}
+
 	public function testBug5223(): void
 	{
 		$this->analyse([__DIR__ . '/../../Analyser/nsrt/bug-5223.php'], [

tests/PHPStan/Rules/Variables/data/bug-4204.php

@@ -0,0 +1,27 @@
+<?php declare(strict_types = 1);
+
+namespace Bug4204;
+
+interface Block
+{
+	public function getSettings(): mixed;
+}
+
+class HelloWorld
+{
+	/**
+	 * @param array<int, object> $blocks
+	 */
+	public function sayHello(array $blocks): void
+	{
+		foreach ($blocks as $block) {
+			$settings = $block->getSettings();
+
+			if (isset($settings['name'])) {
+				// switch name with code key
+				$settings['code'] = $settings['name'];
+				unset($settings['name']);
+			}
+		}
+	}
+}