UnsetCastRule

conf/config.level0.neon

@@ -19,6 +19,7 @@ rules:
 	- PHPStan\Rules\Arrays\DuplicateKeysInLiteralArraysRule
 	- PHPStan\Rules\Arrays\EmptyArrayItemRule
 	- PHPStan\Rules\Arrays\OffsetAccessWithoutDimForReadingRule
+	- PHPStan\Rules\Cast\UnsetCastRule
 	- PHPStan\Rules\Classes\ClassConstantRule
 	- PHPStan\Rules\Classes\DuplicateDeclarationRule
 	- PHPStan\Rules\Classes\ExistingClassesInClassImplementsRule

src/Php/PhpVersion.php

@@ -86,4 +86,9 @@ public function supportsParameterTypeWidening(): bool
 		return $this->versionId >= 70200;
 	}
 
+	public function supportsUnsetCast(): bool
+	{
+		return $this->versionId < 80000;
+	}
+
 }

src/Rules/Cast/UnsetCastRule.php

@@ -0,0 +1,40 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Rules\Cast;
+
+use PhpParser\Node;
+use PHPStan\Analyser\Scope;
+use PHPStan\Php\PhpVersion;
+use PHPStan\Rules\Rule;
+use PHPStan\Rules\RuleErrorBuilder;
+
+/**
+ * @implements Rule<Node\Expr\Cast\Unset_>
+ */
+class UnsetCastRule implements Rule
+{
+
+	private PhpVersion $phpVersion;
+
+	public function __construct(PhpVersion $phpVersion)
+	{
+		$this->phpVersion = $phpVersion;
+	}
+
+	public function getNodeType(): string
+	{
+		return Node\Expr\Cast\Unset_::class;
+	}
+
+	public function processNode(Node $node, Scope $scope): array
+	{
+		if ($this->phpVersion->supportsUnsetCast()) {
+			return [];
+		}
+
+		return [
+			RuleErrorBuilder::message('The (unset) cast is no longer supported in PHP 8.0 and later.')->nonIgnorable()->build(),
+		];
+	}
+
+}

tests/PHPStan/Rules/Cast/UnsetCastRuleTest.php

@@ -0,0 +1,53 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Rules\Cast;
+
+use PHPStan\Php\PhpVersion;
+use PHPStan\Rules\Rule;
+use PHPStan\Testing\RuleTestCase;
+
+/**
+ * @extends RuleTestCase<UnsetCastRule>
+ */
+class UnsetCastRuleTest extends RuleTestCase
+{
+
+	/** @var int */
+	private $phpVersion;
+
+	protected function getRule(): Rule
+	{
+		return new UnsetCastRule(new PhpVersion($this->phpVersion));
+	}
+
+	public function dataRule(): array
+	{
+		return [
+			[
+				70400,
+				[],
+			],
+			[
+				80000,
+				[
+					[
+						'The (unset) cast is no longer supported in PHP 8.0 and later.',
+						6,
+					],
+				],
+			],
+		];
+	}
+
+	/**
+	 * @dataProvider dataRule
+	 * @param int $phpVersion
+	 * @param mixed[] $errors
+	 */
+	public function testRule(int $phpVersion, array $errors): void
+	{
+		$this->phpVersion = $phpVersion;
+		$this->analyse([__DIR__ . '/data/unset-cast.php'], $errors);
+	}
+
+}

tests/PHPStan/Rules/Cast/data/unset-cast.php

@@ -0,0 +1,7 @@
+<?php
+
+namespace UnsetCast;
+
+function ($a): void {
+	$null = (unset) $a;
+};