PHP 8.4: PHP_ZTS and PHP_DEBUG constant value type changed from int to bool

PHP_ZTS and PHP_DEBUG are two PHP global constants that provide information about the current PHP run-time.

• PHP_ZTS: Indicates whether the current build of PHP is thread-safe. The same value as ZEND_THREAD_SAFE constant.
• PHP_DEBUG: Indicates whether the current build of PHP is a debug build. Same value as ZEND_DEBUG_BUILD.

Prior to PHP 8.4, these two constants contained integer values: 0 when disabled, and 1 when enabled. Since PHP 8.4 and later, they have changed to boolean values.

Backward Compatibility Impact

The updated values continue to be "truthy" and "falsy", and type insensitive comparisons such as 1 == true and 0 == false will continue to work even after this change.

Applications that use strict comparisons with PHP_ZTS and PHP_DEBUG constants will need to account for this type change in PHP 8.4.

For compatibility across PHP 8.4 and older versions:

- if (PHP_ZTS === 1) {}
+ if (PHP_ZTS === 1 || PHP_ZTS === true) {}

- if (PHP_DEBUG === 1) {}
+ if (PHP_DEBUG === 1 || PHP_DEBUG === true) {}

For PHP >= 8.4 only:

- if (PHP_ZTS === 1) {}
+ if (PHP_ZTS) {}

- if (PHP_DEBUG === 1) {}
+ if (PHP_DEBUG) {}

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Alternately, PHP_ZTS and PHP_DEBUG constants can be replaced with ZEND_THREAD_SAFE and ZEND_DEBUG_BUILD constants that contain the same values as boolean values across all PHP versions.

- if (PHP_ZTS === 1) {}
+ if (ZEND_THREAD_SAFE) {}

- if (PHP_DEBUG === 1) {}
+ if (ZEND_DEBUG_BUILD) {}

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Implementation