ext/Intl: Fix IntlIterator::current() on invalid iterators (php#22495)

IntlIterator::current() could expose an undefined zval when called before
theiterator is positioned, or after the iterator becomes invalid.

In these cases we directly returns the undefined zval and cause to a UNKNOWN:0
output in userland. Generally, a NULL output would be more proper.

Author: LamentXU123

NEWS

@@ -107,6 +107,8 @@ PHP                                                                        NEWS
     as float rather than int on 64-bit platforms. (Weilin Du)
   . Fixed UConverter::transcode() silently truncating from_subst and to_subst
     option lengths greater than 127 bytes. (Weilin Du)
+  . Fixed IntlIterator::current() to return NULL instead of an undefined value
+    when the iterator is not positioned on a valid element. (Weilin Du)
 
 - IO:
   . Added new polling API. (Jakub Zelenka)

docs/source/core/data-structures/zend_string.rst

@@ -29,9 +29,9 @@ in bytes, and the ``val`` field contains the actual string data.
 
 You may wonder why the ``val`` field is declared as ``char val[1]``. This is called the `struct
 hack`_ in C. It is used to create structs with a flexible size, namely by allowing the last element
-to be expanded arbitrarily. In this case, the size of ``zend_string`` depends on the string's length,
-which is determined at runtime (see ``_ZSTR_STRUCT_SIZE``). When allocating the string, we append
-enough bytes to the allocation to hold the strings content.
+to be expanded arbitrarily. In this case, the size of ``zend_string`` depends on the string's
+length, which is determined at runtime (see ``_ZSTR_STRUCT_SIZE``). When allocating the string, we
+append enough bytes to the allocation to hold the strings content.
 
 .. _struct hack: https://www.geeksforgeeks.org/struct-hack/
 

ext/intl/common/common_enum.cpp

@@ -226,7 +226,7 @@ PHP_METHOD(IntlIterator, current)
 
 	INTLITERATOR_METHOD_FETCH_OBJECT;
 	data = ii->iterator->funcs->get_current_data(ii->iterator);
-	if (data) {
+	if (data && !Z_ISUNDEF_P(data)) {
 		RETURN_COPY_DEREF(data);
 	}
 }

ext/intl/tests/intl_iterator_current_invalid.phpt

@@ -0,0 +1,22 @@
+--TEST--
+IntlIterator::current() returns null when the iterator is not valid
+--EXTENSIONS--
+intl
+--FILE--
+<?php
+$iterator = IntlBreakIterator::createWordInstance('en_US')->getPartsIterator();
+var_dump($iterator->current());
+
+$breakIterator = IntlBreakIterator::createWordInstance('en_US');
+$breakIterator->setText('foo');
+$iterator = $breakIterator->getPartsIterator();
+$iterator->rewind();
+$iterator->next();
+$iterator->next();
+var_dump($iterator->valid());
+var_dump($iterator->current());
+?>
+--EXPECT--
+NULL
+bool(false)
+NULL