PHP RFC: #[Deprecated] Attribute

• Version: 1.1
• Date: 2020-05-06
• Author: Benjamin Ebelei
• Status: Under Discussion
• First Published at: http://wiki.php.net/rfc/deprecated_attribute

With the Attributes RFC accepted for PHP 8, this is a first proposal for an internal attribute hooking into the engine.

It also serves as a good prototype and first step, as usually all languages with attributes also have a Deprecated attribute in their language core.

Developers can put an attribute #[Deprecated] on the following elements (targets):

• Functions
• Methods

For now is not possible to target classes, constants, properties or arguments with this attribute, and it is left for future RFC(s) to address this.

Using attribute will add “ZEND_ACC_DEPERACTED” function flag to the op_array (userland function), which will automatically (with only small changes to the VM) lead to a deprecation warning, when the function is called.

This functionality is present for internal functions already. The Deprecaed attribute allows to expose this feature to userland functions/methods and closes a gap between internal and userland functions.

<?php
 
use Deprecated;
 
#[Deprecated]
function test() {}
// Deprecated: Function test() is deprecated
 
#[Deprecated("use test3() instead")]
function test2() {}
// Deprecated: Function test2() is deprecated, use test3() instead
 
class Foo {
    #[Deprecated]
    public function test() {}
    // Deprecated: Method Foo::test() is deprecated in %s
}

The deprecated class is final and cannot be extended.

Using the deprecated attribute on a function or method behaves the same as putting a call to trigger_error using E_DEPRECATED level as the first line of the same function/method.

While other languages have deprecation attributes, they usually generate compile time warnings instead of runtime warnings. However as PHPs current deprecation model is based on runtime warnings, the Deprecation attribute builds on that existing model. The benefit of a declarative approach with an attribute over the current approach with a function call to trigger_error is that is that it abstracts the implementation details of how deprecations work, with the potential for better integration with future changes to the runtime warning stack of PHP.

Changes to the runtime warning stack of PHP are out of the scope of this RFC.

A class with the name “Deprecated” is introduced into the global namespace.

8.1 for function/method deprecations

None

None

None

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A few things tracked in https://github.com/php/php-src/pull/6521

Accept #[Deprecated] attribute into core?

https://github.com/php/php-src/pull/6521

No implementation for deprecated class constants, properties and parameters yet.