Fix handling of nested generator in zend_test observer

This is the counterpart of phpGH-15952.

Fixes phpGH-16514
Closes phpGH-16530

Author: iluuu1994

ext/zend_test/observer.c

@@ -20,6 +20,7 @@
 #include "zend_observer.h"
 #include "zend_smart_str.h"
 #include "ext/standard/php_var.h"
+#include "zend_generators.h"
 
 static zend_observer_fcall_handlers observer_fcall_init(zend_execute_data *execute_data);
 
@@ -163,6 +164,11 @@ static void observer_show_init_backtrace(zend_execute_data *execute_data)
 	zend_execute_data *ex = execute_data;
 	php_printf("%*s<!--\n", 2 * ZT_G(observer_nesting_depth), "");
 	do {
+		if (UNEXPECTED(!ex->func)) {
+			ex = zend_generator_check_placeholder_frame(ex);
+			ZEND_ASSERT(ex->func);
+		}
+
 		zend_function *fbc = ex->func;
 		int indent = 2 * ZT_G(observer_nesting_depth) + 4;
 		if (fbc->common.function_name) {

ext/zend_test/tests/gh16514.phpt

@@ -0,0 +1,57 @@
+--TEST--
+GH-16514: Nested generator in zend_test observer
+--EXTENSIONS--
+zend_test
+--INI--
+zend_test.observer.enabled=1
+zend_test.observer.show_init_backtrace=1
+--FILE--
+<?php
+
+class Foo {
+    public function __destruct() {
+        debug_print_backtrace();
+    }
+}
+function bar() {
+    yield from foo();
+}
+function foo() {
+    $foo = new Foo();
+    yield;
+}
+$gen = bar();
+foreach ($gen as $dummy);
+
+?>
+--EXPECTF--
+<!-- init '%sgh16514.php' -->
+<!--
+    {main} %sgh16514.php
+-->
+<!-- init bar() -->
+<!--
+    bar()
+    {main} %sgh16514.php
+-->
+<!-- init foo() -->
+<!--
+    foo()
+    bar()
+    {main} %sgh16514.php
+-->
+<!-- init Foo::__destruct() -->
+<!--
+    Foo::__destruct()
+    bar()
+    {main} %sgh16514.php
+-->
+<!-- init debug_print_backtrace() -->
+<!--
+    debug_print_backtrace()
+    Foo::__destruct()
+    bar()
+    {main} %sgh16514.php
+-->
+#0 %s(%d): Foo->__destruct()
+#1 %s(%d): bar()