Deprecate using null as an array offset and when calling array_key_exists()

Author: alexandre-daubois

NEWS

@@ -12,6 +12,8 @@ PHP                                                                        NEWS
     error in PHP 9. (alexandre-daubois)
   . Fixed OSS-Fuzz #439125710 (Pipe cannot be used in write context).
     (nielsdos)
+  . Using null as an array offset and when calling array_key_exists() is now
+    deprecated. Use an emprty string instead. (alexandre-daubois)
 
 - ODBC:
   . Remove ODBCVER and assume ODBC 3.5. (Calvin Buckley)

UPGRADING

@@ -440,6 +440,9 @@ PHP 8.5 UPGRADE NOTES
   . Passing integers outside the interval [0, 255] to chr() is now deprecated.
     This is because a byte can only hold a value within this interval.
     RFC: https://wiki.php.net/rfc/deprecations_php_8_5#deprecate_passing_integers_outside_the_interval_0_255_to_chr
+  . Using null as an array offset and when calling array_key_exists() is now
+    deprecated. Use an empty string instead.
+    RFC: https://wiki.php.net/rfc/deprecations_php_8_5#deprecate_using_values_null_as_an_array_offset_and_when_calling_array_key_exists
 
 - XML:
   . The xml_parser_free() function has been deprecated, as XMLParser objects

Zend/zend_execute.c

@@ -3324,6 +3324,8 @@ static zend_never_inline bool ZEND_FASTCALL zend_array_key_exists_fast(HashTable
 	} else if (Z_TYPE_P(key) <= IS_NULL) {
 		if (UNEXPECTED(Z_TYPE_P(key) == IS_UNDEF)) {
 			ZVAL_UNDEFINED_OP1();
+		} else if (Z_TYPE_P(key) == IS_NULL) {
+			zend_error(E_DEPRECATED, "Using null as an array offset is deprecated, use an empty string instead");
 		}
 		str = ZSTR_EMPTY_ALLOC();
 		goto str_key;

ext/standard/array.c

@@ -6981,6 +6981,7 @@ PHP_FUNCTION(array_key_exists)
 			RETVAL_BOOL(zend_hash_index_exists(ht, Z_LVAL_P(key)));
 			break;
 		case IS_NULL:
+			zend_error(E_DEPRECATED, "Using null as an array offset is deprecated, use an empty string instead");
 			RETVAL_BOOL(zend_hash_exists(ht, ZSTR_EMPTY_ALLOC()));
 			break;
 		case IS_DOUBLE:

ext/standard/tests/array/array_key_exists_null_deprecation.phpt

@@ -0,0 +1,17 @@
+--TEST--
+array_key_exists() with null key shows deprecation warning
+--FILE--
+<?php
+var_dump(array_key_exists(null, []));
+var_dump(array_key_exists(null, ["" => "value"]));
+var_dump(array_key_exists(null, ["key" => "value"]));
+?>
+--EXPECTF--
+Deprecated: Using null as an array offset is deprecated, use an empty string instead in %s on line %d
+bool(false)
+
+Deprecated: Using null as an array offset is deprecated, use an empty string instead in %s on line %d
+bool(true)
+
+Deprecated: Using null as an array offset is deprecated, use an empty string instead in %s on line %d
+bool(false)