Feature request

After phpstan/phpstan-src#3746 there is still ground left that could be covered with static analysis. The following lists consist of ~30 todos that could be implemented for robust checks around property hooks.

PHP RFC

Fatal declarations

These situations make PHP fatal-error immediately during the class loading. This is easy low hanging fruit.

• Hooked properties cannot be readonly
• Readonly classes cannot have hooked properties
• Final property before 8.4
• Static properties cannot be hooked
• Virtual property cannot have default value
• hooked properties cannot be unset()
• Returning by reference from a void function is deprecated - &set
• Check parameters in get and set hooks, count, no default values, no byRef, no variadic, no promoted
• If a trait and a class where it is used both declare the same property with hooks, an error is issued.
• Abstract property from interface/abstract class should be implemented in non-abstract class
• Interface prescribes whether implemented property should be publicly readable and writable. This can be accomplished in many ways, with virtual or non-virtual properties, with or without hooks.
• A get hook in an interface may be satisfied by either a get or &get hook in a class. An interface may alternatively specify a &get hook in its definition, in which case an implementing class must also use a &get hook. This behavior is identical to how methods in interfaces already work.
• Of note, an interface property that only requires get may be satisfied by a public readonly property, as the restrictions of readonly only apply on write. However, an interface property that requires set is incompatible with a readonly property, as public-write would be disallowed.
• With abstract properties (on an interface or abstract class) or virtual properties, it is possible to declare a property that has only a get or set operation. As a result, abstract properties or virtual properties that have only a get operation required MAY be covariant. Similarly, an abstract property or virtual property that has only a set operation required MAY be contravariant. Once a property has both a get and set operation, however, it is no longer covariant or contravariant for further extension. That is, it is now invariant (as all properties are in 8.3 and earlier).
• A readonly property with a get or set hook is disallowed and will throw a compile error. That also means that a child class may not redeclare and add hooks to a readonly property, either.
• Check overriden hook from parent - final hook cannot be overriden, check set hook contravariance, maybe more checks
• Detect hook duplicates - multiple get, get and &get etc.
• Abstract private not allowed
• Final private not allowed
• Cross-check same properties inherited from multiple interfaces in a single class

Property hook body checks

• Unused set hook parameter
• Disallow magic access like $this->{‘haha’} inside hooks for virtual properties
• Hook calls a method, method tries to access the same hooked property - PHP errors, PHPStan should detect it.

Behaviour checks & changes

• Accessing parent hooks check parent::$propName::get(), MutatingScope::resolveType support
• processAssignVar: with $isAssignOp true both get hooks and set hooks throw points should be considered
• __PROPERTY__ exists only on 8.4+
• Ability to mark get hooks as pure or impure
• phpstan-deprecation-rules rule for invoking deprecated set/get hook
• Writing array index to hooked property not always allowed, depends on a table described in the RFC
• the presence of a set hook must necessarily also disallow acquiring a reference to a property
• A caller may only obtain a reference to a property that has declared &get. Attempting to get a reference on a get property will trigger an error.
• Casting object to array - skip virtual properties
• the #[\Override] attribute can be applied to a hook, and it will treat the parent property's hook as its parent and behave accordingly.
• Support for stub files - @param above set hook. This might already work thanks to createUserlandMethodReflection but needs to be tested.

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