Add next handler parameter to zend_observer_remove_begin/end_handler

UPGRADING.INTERNALS

@@ -77,6 +77,10 @@ PHP 8.4 INTERNALS UPGRADE NOTES
   void(*)(void *, size_t) to
   void(*)(void *, size_t ZEND_FILE_LINE_DC ZEND_FILE_LINE_ORIG_DC)
 
+* zend_observer_remove_begin_handler() and zend_observer_remove_end_handler()
+  got each a new parameter returning an observer which must be called, if the
+  removal happened during observer execution.
+
 
 ========================
 2. Build system changes

Zend/zend_observer.c

@@ -147,19 +147,26 @@ static void zend_observer_fcall_install(zend_execute_data *execute_data)
 	}
 }
 
-static bool zend_observer_remove_handler(void **first_handler, void *old_handler) {
+/* We need to provide the ability to retrieve the handler which will move onto the position the current handler was.
+ * The fundamental problem is that, if a handler is removed while it's being executed, it will move handlers around:
+ * the previous next handler is now at the place where the current handler was.
+ * Hence, the next handler executed will be the one after the next handler.
+ * Callees must thus invoke the next handler themselves, with the same arguments they were passed. */
+static bool zend_observer_remove_handler(void **first_handler, void *old_handler, void **next_handler) {
 	size_t registered_observers = zend_observers_fcall_list.count;
 
 	void **last_handler = first_handler + registered_observers - 1;
 	for (void **cur_handler = first_handler; cur_handler <= last_handler; ++cur_handler) {
 		if (*cur_handler == old_handler) {
 			if (registered_observers == 1 || (cur_handler == first_handler && cur_handler[1] == NULL)) {
 				*cur_handler = ZEND_OBSERVER_NOT_OBSERVED;
+				*next_handler = NULL;
 			} else {
 				if (cur_handler != last_handler) {
 					memmove(cur_handler, cur_handler + 1, sizeof(cur_handler) * (last_handler - cur_handler));
 				}
 				*last_handler = NULL;
+				*next_handler = *cur_handler;
 			}
 			return true;
 		}
@@ -184,8 +191,8 @@ ZEND_API void zend_observer_add_begin_handler(zend_function *function, zend_obse
 	}
 }
 
-ZEND_API bool zend_observer_remove_begin_handler(zend_function *function, zend_observer_fcall_begin_handler begin) {
-	return zend_observer_remove_handler((void **)&ZEND_OBSERVER_DATA(function), begin);
+ZEND_API bool zend_observer_remove_begin_handler(zend_function *function, zend_observer_fcall_begin_handler begin, zend_observer_fcall_begin_handler *next) {
+	return zend_observer_remove_handler((void **)&ZEND_OBSERVER_DATA(function), begin, (void **)next);
 }
 
 ZEND_API void zend_observer_add_end_handler(zend_function *function, zend_observer_fcall_end_handler end) {
@@ -200,9 +207,9 @@ ZEND_API void zend_observer_add_end_handler(zend_function *function, zend_observ
 	*end_handler = end;
 }
 
-ZEND_API bool zend_observer_remove_end_handler(zend_function *function, zend_observer_fcall_end_handler end) {
+ZEND_API bool zend_observer_remove_end_handler(zend_function *function, zend_observer_fcall_end_handler end, zend_observer_fcall_end_handler *next) {
 	size_t registered_observers = zend_observers_fcall_list.count;
-	return zend_observer_remove_handler((void **)&ZEND_OBSERVER_DATA(function) + registered_observers, end);
+	return zend_observer_remove_handler((void **)&ZEND_OBSERVER_DATA(function) + registered_observers, end, (void **)next);
 }
 
 static inline zend_execute_data **prev_observed_frame(zend_execute_data *execute_data) {

Zend/zend_observer.h

@@ -62,9 +62,9 @@ ZEND_API void zend_observer_fcall_register(zend_observer_fcall_init);
 // Call during runtime, but only if you have used zend_observer_fcall_register.
 // You must not have more than one begin and one end handler active at the same time. Remove the old one first, if there is an existing one.
 ZEND_API void zend_observer_add_begin_handler(zend_function *function, zend_observer_fcall_begin_handler begin);
-ZEND_API bool zend_observer_remove_begin_handler(zend_function *function, zend_observer_fcall_begin_handler begin);
+ZEND_API bool zend_observer_remove_begin_handler(zend_function *function, zend_observer_fcall_begin_handler begin, zend_observer_fcall_begin_handler *next);
 ZEND_API void zend_observer_add_end_handler(zend_function *function, zend_observer_fcall_end_handler end);
-ZEND_API bool zend_observer_remove_end_handler(zend_function *function, zend_observer_fcall_end_handler end);
+ZEND_API bool zend_observer_remove_end_handler(zend_function *function, zend_observer_fcall_end_handler end, zend_observer_fcall_end_handler *next);
 
 ZEND_API void zend_observer_startup(void); // Called by engine before MINITs
 ZEND_API void zend_observer_post_startup(void); // Called by engine after MINITs

ext/zend_test/observer.c

@@ -297,8 +297,9 @@ static ZEND_INI_MH(zend_test_observer_OnUpdateCommaList)
 	if (stage != PHP_INI_STAGE_STARTUP && stage != PHP_INI_STAGE_ACTIVATE && stage != PHP_INI_STAGE_DEACTIVATE && stage != PHP_INI_STAGE_SHUTDOWN) {
 		ZEND_HASH_FOREACH_STR_KEY(*p, funcname) {
 			if ((func = zend_hash_find_ptr(EG(function_table), funcname))) {
-				zend_observer_remove_begin_handler(func, observer_begin);
-				zend_observer_remove_end_handler(func, observer_end);
+				void *old_handler;
+				zend_observer_remove_begin_handler(func, observer_begin, (zend_observer_fcall_begin_handler *)&old_handler);
+				zend_observer_remove_end_handler(func, observer_end, (zend_observer_fcall_end_handler *)&old_handler);
 			}
 		} ZEND_HASH_FOREACH_END();
 	}