PHP: Unknown property hooks are accepted inside discarded declarations #24795

Description

Summary

PHP 8.5 and PHP 8.6 accept unknown property-hook names when the enclosing declaration is discarded during compilation, even though the same declaration is rejected when retained or compiled normally.

This creates a discrepancy in compile-time validation depending on whether the enclosing expression or declaration survives constant folding.

Minimal reproducer

<?php
false && static function() {
    return new class {
        public int $x {
            unknown => 1;
        }
    };
};

Actual behavior:

• PHP 8.5.10: Compilation succeeds.
• PHP 8.6.0RC4: Compilation succeeds.

Retained declaration control

<?php
$f = static function() {
    return new class {
        public int $x {
            unknown => 1;
        }
    };
};

Both PHP 8.5.10 and PHP 8.6.0RC4 reject this during compilation.

The reported diagnostic is:

Fatal error: Unknown hook "unknown" for property class@anonymous::$x, expected "get" or "set"

Ordinary class declaration control

<?php
class C {
    public int $x {
        unknown => 1;
    }
}

Both versions reject this with:

Fatal error: Unknown hook "unknown" for property C::$x, expected "get" or "set"

Valid property-hook control

<?php
class C {
    public int $x {
        get => 1;
    }
}

Both versions compile successfully.

Additional discarded-expression example

The following also compiles successfully in both PHP 8.5.10 and PHP 8.6.0RC4:

<?php
const F = true ? 1 : static function() {
    return new class {
        public int $x {
            unknown => 1;
        }
    };
};

Expected behavior / clarification requested

Should PHP reject an unknown property-hook name regardless of whether its enclosing declaration survives compilation?

Specifically, should the discarded closure and conditional-expression examples above fail compilation, or is their acceptance intentional?

If acceptance is intentional, what defines the boundary between declarations that must undergo property-hook validation and declarations eliminated during compilation?

The question concerns compile-time source validity, not runtime evaluation of unreachable branches.

Affected versions

• PHP 8.5.10 — Windows x64
• PHP 8.6.0RC4 — Windows x64, NTS, VC2022
• PHP 8.6 source commit: f23b4c222cebe33be93ee8ecaaa14390c5507a08

The PHP 8.6 executable was built from the specified source commit.

Reproduce by saving each example separately and running:

php -n -l example.php

Relevant implementation

• [Property-hook parser productions](

  php-src/Zend/zend_language_parser.y

  Line 1160 in f23b4c2

  property_hook:

  )
• [zend_get_property_hook_kind_from_name](

  php-src/Zend/zend_compile.c

  Line 9348 in f23b4c2

  zend_property_hook_kind zend_get_property_hook_kind_from_name(const zend_string *name) {

  )
• [Property-hook compilation](

  php-src/Zend/zend_compile.c

  Line 9409 in f23b4c2

  zend_property_hook_kind hook_kind = zend_get_property_hook_kind_from_name(name);

  )

The parser permits hook names represented by T_STRING, while compiler validation recognizes get and set.

The observed acceptance appears to depend on whether compilation visits the enclosing declaration.

I would appreciate clarification on whether this is intended behaviour or a missing validation step for discarded declarations.

PHP Version

PHP 8.6.0RC4 (cli) (built: Oct 25 2026 12:45:36) (NTS Visual C++ 2022 x64)
Copyright © The PHP Group and Contributors
Zend Engine v4.6.0RC4, Copyright © Zend by Perforce
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Operating System

Windows x64 (64-bit), MSVC 2022 build