Fix GH-23301: nested "yield from" yields a value twice when the middle generator ends with "yield from []"

Author: lazerg

NEWS

@@ -5,6 +5,8 @@ PHP                                                                        NEWS
 - Core:
   . Fixed bug GH-15375 (Nested "yield from" skips items after a valid() or
     next() call on the inner generator). (iliaal)
+  . Fixed bug GH-23301 (Nested "yield from" yields a value twice when the
+    middle generator ends with "yield from []"). (Lazizbek Ergashev)
 
 - Opcache:
   . Fixed opcache.protect_memory race under ZTS. (realFlowControl)

Zend/tests/generators/gh23301.phpt

@@ -0,0 +1,29 @@
+--TEST--
+GH-23301 (Nested "yield from" yields a value twice when the middle generator ends with "yield from []")
+--FILE--
+<?php
+
+function inner() {
+    yield "B";
+}
+
+function middle() {
+    yield "A";
+    yield from inner();
+    yield "C";
+    yield from [];
+}
+
+function outer() {
+    yield from middle();
+}
+
+foreach (outer() as $value) {
+    echo $value, "\n";
+}
+
+?>
+--EXPECT--
+A
+B
+C

Zend/zend_generators.c

@@ -890,7 +890,7 @@ ZEND_API void zend_generator_resume(zend_generator *orig_generator) /* {{{ */
 
 	/* yield from was used, try another resume. */
 	if (UNEXPECTED(generator->execute_data && generator->execute_data->opline->opcode == ZEND_YIELD_FROM)) {
-		delegator = generator;
+		delegator = generator->node.parent ? generator : orig_generator;
 		generator = zend_generator_get_current(orig_generator);
 		goto try_again;
 	}