Document hasRestrictedWriteAccess: explain difference from private properties and why private(get) is not needed

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: phpstan-bot

src/Rules/Generics/PropertyVarianceRule.php

@@ -56,6 +56,21 @@ public function processNode(Node $node, Scope $scope): array
 		);
 	}
 
+	/**
+	 * Checks whether a non-private property is not publicly writable.
+	 *
+	 * This differs from a fully private property (handled by the early return above):
+	 * a private property is completely inaccessible externally, so variance is irrelevant
+	 * and is skipped entirely. Here, the property IS publicly readable (covariant/output
+	 * position) but write access is restricted — either via private(set) which limits
+	 * writes to the declaring class, or via a get-only hook with no set hook.
+	 * Since the write side is not part of the public API, only the read (covariant)
+	 * position matters, same as readonly.
+	 *
+	 * There is no need for a symmetric private(get) check because PHP 8.4's asymmetric
+	 * visibility only allows restricting set visibility — the set visibility must be
+	 * equal to or more restrictive than the read visibility, so private(get) does not exist.
+	 */
 	private function hasRestrictedWriteAccess(ClassPropertyNode $node): bool
 	{
 		if ($node->isPrivateSet()) {