Verify property type after unset

src/Analyser/MutatingScope.php

@@ -37,6 +37,7 @@
 use PHPStan\Node\Expr\PropertyInitializationExpr;
 use PHPStan\Node\Expr\SetOffsetValueTypeExpr;
 use PHPStan\Node\Expr\TypeExpr;
+use PHPStan\Node\Expr\UnsetOffsetExpr;
 use PHPStan\Node\IssetExpr;
 use PHPStan\Node\Printer\ExprPrinter;
 use PHPStan\Parser\ArrayMapArgVisitor;
@@ -639,6 +640,9 @@ public function getType(Expr $node): Type
 		if ($node instanceof GetOffsetValueTypeExpr) {
 			return $this->getType($node->getVar())->getOffsetValueType($this->getType($node->getDim()));
 		}
+		if ($node instanceof UnsetOffsetExpr) {
+			return $this->getType($node->getVar())->unsetOffset($this->getType($node->getDim()));
+		}
 		if ($node instanceof SetOffsetValueTypeExpr) {
 			return $this->getType($node->getVar())->setOffsetValueType(
 				$node->getDim() !== null ? $this->getType($node->getDim()) : null,

src/Analyser/NodeScopeResolver.php

@@ -78,6 +78,7 @@
 use PHPStan\Node\Expr\OriginalPropertyTypeExpr;
 use PHPStan\Node\Expr\PropertyInitializationExpr;
 use PHPStan\Node\Expr\SetOffsetValueTypeExpr;
+use PHPStan\Node\Expr\UnsetOffsetExpr;
 use PHPStan\Node\FinallyExitPointsNode;
 use PHPStan\Node\FunctionCallableNode;
 use PHPStan\Node\FunctionReturnStatementsNode;
@@ -1510,9 +1511,32 @@ private function processStmtNode(
 			$throwPoints = [];
 			foreach ($stmt->vars as $var) {
 				$scope = $this->lookForSetAllowedUndefinedExpressions($scope, $var);
-				$scope = $this->processExprNode($stmt, $var, $scope, $nodeCallback, ExpressionContext::createDeep())->getScope();
+				$exprResult = $this->processExprNode($stmt, $var, $scope, $nodeCallback, ExpressionContext::createDeep());
+				$scope = $exprResult->getScope();
 				$scope = $this->lookForUnsetAllowedUndefinedExpressions($scope, $var);
-				$scope = $scope->unsetExpression($var);
+				$hasYield = $hasYield || $exprResult->hasYield();
+				$throwPoints = array_merge($throwPoints, $exprResult->getThrowPoints());
+				if ($var instanceof ArrayDimFetch && $var->dim !== null) {
+					$scope = $this->processAssignVar(
+						$scope,
+						$stmt,
+						$var->var,
+						new UnsetOffsetExpr($var->var, $var->dim),
+						static function (Node $node, Scope $scope) use ($nodeCallback): void {
+							if (!$node instanceof PropertyAssignNode) {
+								return;
+							}
+
+							$nodeCallback($node, $scope);
+						},
+						ExpressionContext::createDeep(),
+						static fn (MutatingScope $scope): ExpressionResult => new ExpressionResult($scope, false, []),
+						false,
+					)->getScope();
+				} else {
+					$scope = $scope->invalidateExpression($var);
+				}
+
 			}
 		} elseif ($stmt instanceof Node\Stmt\Use_) {
 			$hasYield = false;

src/Node/Expr/UnsetOffsetExpr.php

@@ -0,0 +1,39 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Node\Expr;
+
+use PhpParser\Node\Expr;
+use PHPStan\Node\VirtualNode;
+
+class UnsetOffsetExpr extends Expr implements VirtualNode
+{
+
+	public function __construct(private Expr $var, private Expr $dim)
+	{
+		parent::__construct([]);
+	}
+
+	public function getVar(): Expr
+	{
+		return $this->var;
+	}
+
+	public function getDim(): Expr
+	{
+		return $this->dim;
+	}
+
+	public function getType(): string
+	{
+		return 'PHPStan_Node_UnsetOffsetExpr';
+	}
+
+	/**
+	 * @return string[]
+	 */
+	public function getSubNodeNames(): array
+	{
+		return [];
+	}
+
+}

src/Node/Printer/Printer.php

@@ -11,6 +11,7 @@
 use PHPStan\Node\Expr\PropertyInitializationExpr;
 use PHPStan\Node\Expr\SetOffsetValueTypeExpr;
 use PHPStan\Node\Expr\TypeExpr;
+use PHPStan\Node\Expr\UnsetOffsetExpr;
 use PHPStan\Node\IssetExpr;
 use PHPStan\Type\VerbosityLevel;
 use function sprintf;
@@ -33,6 +34,11 @@ protected function pPHPStan_Node_GetOffsetValueTypeExpr(GetOffsetValueTypeExpr $
 		return sprintf('__phpstanGetOffsetValueType(%s, %s)', $this->p($expr->getVar()), $this->p($expr->getDim()));
 	}
 
+	protected function pPHPStan_Node_UnsetOffsetExpr(UnsetOffsetExpr $expr): string // phpcs:ignore
+	{
+		return sprintf('__phpstanUnsetOffset(%s, %s)', $this->p($expr->getVar()), $this->p($expr->getDim()));
+	}
+
 	protected function pPHPStan_Node_GetIterableValueTypeExpr(GetIterableValueTypeExpr $expr): string // phpcs:ignore
 	{
 		return sprintf('__phpstanGetIterableValueType(%s)', $this->p($expr->getExpr()));

tests/PHPStan/Rules/Properties/TypesAssignedToPropertiesRuleTest.php

@@ -586,4 +586,26 @@ public function testBug7087(): void
 		$this->analyse([__DIR__ . '/data/bug-7087.php'], []);
 	}
 
+	public function testUnset(): void
+	{
+		$this->checkExplicitMixed = true;
+		$this->analyse([__DIR__ . '/data/property-type-after-unset.php'], [
+			[
+				'Property PropertyTypeAfterUnset\Foo::$nonEmpty (non-empty-array<int>) does not accept array<int>.',
+				19,
+				'array<int> might be empty.',
+			],
+			[
+				'Property PropertyTypeAfterUnset\Foo::$listProp (list<int>) does not accept array<int<0, max>, int>.',
+				20,
+				'array<int<0, max>, int> might not be a list.',
+			],
+			[
+				'Property PropertyTypeAfterUnset\Foo::$nestedListProp (array<list<int>>) does not accept non-empty-array<array<int<0, max>, int>>.',
+				21,
+				'array<int<0, max>, int> might not be a list.',
+			],
+		]);
+	}
+
 }

tests/PHPStan/Rules/Properties/data/property-type-after-unset.php

@@ -0,0 +1,24 @@
+<?php
+
+namespace PropertyTypeAfterUnset;
+
+class Foo
+{
+
+	/** @var non-empty-array<int> */
+	private $nonEmpty;
+
+	/** @var list<int> */
+	private $listProp;
+
+	/** @var array<list<int>> */
+	private $nestedListProp;
+
+	public function doFoo(int $i, int $j)
+	{
+		unset($this->nonEmpty[$i]);
+		unset($this->listProp[$i]);
+		unset($this->nestedListProp[$i][$j]);
+	}
+
+}