ReadOnlyPropertyRule

conf/config.level0.neon

@@ -75,6 +75,7 @@ rules:
 	- PHPStan\Rules\Properties\AccessPropertiesInAssignRule
 	- PHPStan\Rules\Properties\AccessStaticPropertiesInAssignRule
 	- PHPStan\Rules\Properties\PropertyAttributesRule
+	- PHPStan\Rules\Properties\ReadOnlyPropertyRule
 	- PHPStan\Rules\Variables\UnsetRule
 
 services:

src/Php/PhpVersion.php

@@ -137,4 +137,9 @@ public function supportsFinalConstants(): bool
 		return $this->versionId >= 80100;
 	}
 
+	public function supportsReadOnlyProperties(): bool
+	{
+		return $this->versionId >= 80100;
+	}
+
 }

src/Rules/Properties/ReadOnlyPropertyRule.php

@@ -0,0 +1,52 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Rules\Properties;
+
+use PhpParser\Node;
+use PHPStan\Analyser\Scope;
+use PHPStan\Node\ClassPropertyNode;
+use PHPStan\Php\PhpVersion;
+use PHPStan\Rules\Rule;
+use PHPStan\Rules\RuleErrorBuilder;
+
+/**
+ * @implements Rule<ClassPropertyNode>
+ */
+class ReadOnlyPropertyRule implements Rule
+{
+
+	private PhpVersion $phpVersion;
+
+	public function __construct(PhpVersion $phpVersion)
+	{
+		$this->phpVersion = $phpVersion;
+	}
+
+	public function getNodeType(): string
+	{
+		return ClassPropertyNode::class;
+	}
+
+	public function processNode(Node $node, Scope $scope): array
+	{
+		if (!$node->isReadOnly()) {
+			return [];
+		}
+
+		$errors = [];
+		if (!$this->phpVersion->supportsReadOnlyProperties()) {
+			 $errors[] = RuleErrorBuilder::message('Readonly properties are supported only on PHP 8.1 and later.')->nonIgnorable()->build();
+		}
+
+		if ($node->getNativeType() === null) {
+			 $errors[] = RuleErrorBuilder::message('Readonly property must have a native type.')->nonIgnorable()->build();
+		}
+
+		if ($node->getDefault() !== null) {
+			 $errors[] = RuleErrorBuilder::message('Readonly property cannot have a default value.')->nonIgnorable()->build();
+		}
+
+		return $errors;
+	}
+
+}

tests/PHPStan/Rules/Properties/ReadOnlyPropertyRuleTest.php

@@ -0,0 +1,82 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Rules\Properties;
+
+use PHPStan\Php\PhpVersion;
+use PHPStan\Rules\Rule;
+use PHPStan\Testing\RuleTestCase;
+
+/**
+ * @extends RuleTestCase<ReadOnlyPropertyRule>
+ */
+class ReadOnlyPropertyRuleTest extends RuleTestCase
+{
+
+	/** @var int */
+	private $phpVersionId;
+
+	protected function getRule(): Rule
+	{
+		return new ReadOnlyPropertyRule(new PhpVersion($this->phpVersionId));
+	}
+
+	public function dataRule(): array
+	{
+		return [
+			[
+				80000,
+				[
+					[
+						'Readonly properties are supported only on PHP 8.1 and later.',
+						8,
+					],
+					[
+						'Readonly properties are supported only on PHP 8.1 and later.',
+						9,
+					],
+					[
+						'Readonly property must have a native type.',
+						9,
+					],
+					[
+						'Readonly properties are supported only on PHP 8.1 and later.',
+						10,
+					],
+					[
+						'Readonly property cannot have a default value.',
+						10,
+					],
+				],
+			],
+			[
+				80100,
+				[
+					[
+						'Readonly property must have a native type.',
+						9,
+					],
+					[
+						'Readonly property cannot have a default value.',
+						10,
+					],
+				],
+			],
+		];
+	}
+
+	/**
+	 * @dataProvider dataRule
+	 * @param int $phpVersionId
+	 * @param mixed[] $errors
+	 */
+	public function testRule(int $phpVersionId, array $errors): void
+	{
+		if (!self::$useStaticReflectionProvider) {
+			$this->markTestSkipped('Test requires static reflection.');
+		}
+
+		$this->phpVersionId = $phpVersionId;
+		$this->analyse([__DIR__ . '/data/read-only-property.php'], $errors);
+	}
+
+}

tests/PHPStan/Rules/Properties/data/read-only-property.php

@@ -0,0 +1,12 @@
+<?php // lint >= 8.1
+
+namespace ReadOnlyProperty;
+
+class Foo
+{
+
+	private readonly int $foo;
+	private readonly $bar;
+	private readonly int $baz = 0;
+
+}