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Extensions.md

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PHP/Extensions

Configure PHP extensions.

This module is responsible for parsing CMakeLists.txt files of PHP extensions and sorting extensions based on the dependencies listed in the add_dependencies(). If an extension has specified dependencies, it ensures that all dependencies are automatically enabled. If any of the dependencies are built as SHARED libraries, the extension must also be built as a SHARED library.

Dependencies can be specified on top of the CMake's built-in command add_dependencies(), which builds target dependencies before the target itself. This module reads the add_dependencies() invocations in extensions CMakeLists.txt files and automatically enables and configures them as SHARED depending on the configuration if they haven't been explicitly configured. If it fails to configure extension dependencies automatically it will result in a fatal error at the end of the configuration phase.

Order of the extensions is then also important in the generated main/internal_functions*.c files (for the list of phpext_<extension>_ptr in the zend_module_entry php_builtin_extensions). This is the order of how the modules are registered into the Zend hash table.

PHP internal API also provides dependencies handling with the ZEND_MOD_REQUIRED, ZEND_MOD_CONFLICTS, and ZEND_MOD_OPTIONAL, which should be set in the extension code itself. PHP internally then sorts the extensions based on the ZEND_MOD_REQUIRED and ZEND_MOD_OPTIONAL, so build time sorting shouldn't be taken for granted and is mostly used for php-src builds.

Example why setting dependencies with ZEND_MOD_REQUIRED might matter: https://bugs.php.net/53141

Custom CMake properties

  • PHP_ZEND_EXTENSION

    Extensions can utilize this custom target property, which designates the extension as a Zend extension rather than a standard PHP extension. Zend extensions function similarly to regular PHP extensions, but they are loaded using the zend_extension INI directive and possess an internally distinct structure with additional hooks. Typically employed for advanced functionalities like debuggers and profilers, Zend extensions offer enhanced capabilities.

    set_target_properties(php_ext_<extension_name> PROPERTIES PHP_ZEND_EXTENSION TRUE)

  • PHP_EXTENSION_<extension>_DEPS

    Global property with a list of all dependencies of (name of the extension as named in ext directory).

Basic usage

# CMakeLists.txt
include(PHP/Extensions)