PHP 7.4 INTERNALS UPGRADE NOTES

1. Internal API changes
  a. php_sys_symlink() and php_sys_link()
  b. zend_lookup_class_ex() and zend_fetch_class_by_name()
  c. Function/property/class flags
  d. Removed zend_check_private()
  e. php_win32_error_to_msg() memory management
  f. get_properties_for() handler / Z_OBJDEBUG_P

2. Build system changes
  a. Abstract
  b. Unix build system changes
  c. Windows build system changes

3. Module changes
  a. ext/xml
  b. ext/hash

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1. Internal API changes
========================

 a. php_sys_symlink() and php_sys_link() portability macros have been
    added, which behave like POSIX's symlink() and link(), respectively, on
    POSIX compliant systems and on Windows.

 b. zend_lookup_class_ex() and zend_fetch_class_by_name() prototypes were
    changed to accept optional lower-case class name as zend_string*,
    instead of zval*.

 c. Function/property/class flags changes
    - ZEND_ACC_CTOR and ZEND_ACC_DTOR are removed. It's possible to check if
      method is a constructor/destructor using the following condition
      (func->commpon.scope->constructor == func).
    - ZEND_ACC_IMPLEMENTED_ABSTRACT is removed (it was used only internally
      during inheritance).
    - ZEND_ACC_IMPLICIT_PUBLIC is removed (it was used only for reflection)
    - ZEND_ACC_SHADOW property flag is removed. Instead of creating shadow
      clone, now we use the same private property_info, and should also
      check property_info->ce (in the same way as with methods).
    - ZEND_ACC_ANON_BOUND is replaced with ZEND_ACC_LINKED. This flag is set
      not only during anonymous classes declaration, but also during any
      run-time or compile-time class declaration.
    - ZEND_ACC_NO_RT_ARENA renamed into ZEND_ACC_HEAP_RT_CACHE. Now it's used
      not only for closures, but also for pseudo-main op_arrays.
    - ZEND_ACC_... flags are re-numbered.

  d. zend_check_private() is removed. Use (func->common.scope == scope) instead.

  e. Pointers returned by php_win32_error_to_msg() have to be freed using
     php_win32_error_msg_free(). Same regarding php_win_err() vs.
     php_win_err_free().

  f. A new, optional object handler with the signature

         HashTable *get_properties_for(zval *obj, zend_prop_purpose purpose)

     has been introduced, where zend_prop_purpose (currently) takes one of:

         ZEND_PROP_PURPOSE_DEBUG       // var_dump etc.
         ZEND_PROP_PURPOSE_ARRAY_CAST  // (array) $obj
         ZEND_PROP_PURPOSE_SERIALIZE   // "O"-format serialization (__wakeup)
         ZEND_PROP_PURPOSE_VAR_EXPORT  // var_export (__set_state)
         ZEND_PROP_PURPOSE_JSON        // json_encode

     The handler returns a non-null HashTable with increased refcounted, and
     the return value must be released using zend_release_properties().

     This handler serves the same general function as get_properties(), but
     provides more control over different property uses, while also making
     it possible to return a temporary property table.

     get_properties() is still used in cases where none of the above purposes
     apply, but overloading get_properties() is generally discouraged. If you
     want to provide purposes for general usage rather than just debugging or
     serialization, please prefer using properly declared properties.

     get_debug_info() is superseded by get_properties_for() with the
     ZEND_PROP_PURPOSE_DEBUG purpose, but remains available for backwards-
     compatibility reasons. However, while it is fine to define this handler,
     it should never be directly called by consuming code.

     The Z_OBJDEBUG_P macro has been removed. It should be replaced by calls to
     zend_get_properties_for() with the ZEND_PROP_PURPOSE_DEBUG purpose:

         // OLD
         int is_temp;
         HashTable *ht = Z_OBJDEBUG_P(obj, is_temp);
         // ...
         if (is_temp) {
            zend_hash_destroy(ht);
            FREE_HASHTABLE(ht);
         }

         // NEW
         HashTable *ht = zend_get_properties_for(obj, ZEND_PROP_PURPOSE_DEBUG);
         // ...
         zend_release_properties(ht);

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2. Build system changes
========================

  a. Abstract
    - The hash extension is now always available, meaning the --enable-hash
	  configure argument has been removed.

  b. Unix build system changes
    - configure --help now also outputs --program-suffix and --program-prefix
      information by using the Autoconf AC_ARG_PROGRAM macro.
    - Obsolescent macros AC_FUNC_VPRINTF and AC_FUNC_UTIME_NULL have been
      removed. Symbols HAVE_VPRINTF and HAVE_UTIME_NULL are no longer defined
      since they are not needed on the current systems.

  c. Windows build system changes

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3. Module changes
========================

  a. ext/xml
    - The public (internal) API of the ext/xml extension has been removed. All
      functions and structures are private to the extension now.

  b. ext/hash
    - The hash extension is now always available, allowing extensions to rely
	  on its functionality to be available without compile time checks.