Merge branch 'PHP-8.3' into PHP-8.4

* PHP-8.3:
  Fix GH-19303: Unpacking empty packed array into uninitialized array causes assertion failure

Author: nielsdos

NEWS

@@ -15,6 +15,8 @@ PHP                                                                        NEWS
     binary const expr). (ilutov)
   . Fixed bug GH-19305 (Operands may be being released during comparison).
     (Arnaud)
+  . Fixed bug GH-19303 (Unpacking empty packed array into uninitialized array
+    causes assertion failure). (nielsdos)
 
 - FTP:
   . Fix theoretical issues with hrtime() not being available. (nielsdos)

Zend/tests/array_unpack/gh19303.phpt

@@ -0,0 +1,11 @@
+--TEST--
+GH-19303 (Unpacking empty packed array into uninitialized array causes assertion failure)
+--FILE--
+<?php
+$a = [0];
+unset($a[0]);
+var_dump([...$a]);
+?>
+--EXPECT--
+array(0) {
+}

Zend/zend_vm_def.h

@@ -6262,17 +6262,22 @@ ZEND_VM_C_LABEL(add_unpack_again):
 		zval *val;
 
 		if (HT_IS_PACKED(ht) && (zend_hash_num_elements(result_ht) == 0 || HT_IS_PACKED(result_ht))) {
-			zend_hash_extend(result_ht, result_ht->nNumUsed + zend_hash_num_elements(ht), 1);
-			ZEND_HASH_FILL_PACKED(result_ht) {
-				ZEND_HASH_PACKED_FOREACH_VAL(ht, val) {
-					if (UNEXPECTED(Z_ISREF_P(val)) &&
-						UNEXPECTED(Z_REFCOUNT_P(val) == 1)) {
-						val = Z_REFVAL_P(val);
-					}
-					Z_TRY_ADDREF_P(val);
-					ZEND_HASH_FILL_ADD(val);
-				} ZEND_HASH_FOREACH_END();
-			} ZEND_HASH_FILL_END();
+			/* zend_hash_extend() skips initialization when the number of elements is 0,
+			 * but the code below expects that result_ht is initialized as packed.
+			 * We can just skip the work in that case. */
+			if (result_ht->nNumUsed + zend_hash_num_elements(ht) > 0) {
+				zend_hash_extend(result_ht, result_ht->nNumUsed + zend_hash_num_elements(ht), 1);
+				ZEND_HASH_FILL_PACKED(result_ht) {
+					ZEND_HASH_PACKED_FOREACH_VAL(ht, val) {
+						if (UNEXPECTED(Z_ISREF_P(val)) &&
+							UNEXPECTED(Z_REFCOUNT_P(val) == 1)) {
+							val = Z_REFVAL_P(val);
+						}
+						Z_TRY_ADDREF_P(val);
+						ZEND_HASH_FILL_ADD(val);
+					} ZEND_HASH_FOREACH_END();
+				} ZEND_HASH_FILL_END();
+			}
 		} else {
 			zend_string *key;