Fix GH-20194 without opcache

Author: Girgias

Zend/tests/offsets/gh20194.phpt

@@ -0,0 +1,17 @@
+--TEST--
+GH-20194: Using null as an array offset does not emit deprecation when resolved at compile time
+--INI--
+opcache.opt_debug_level=0x20000
+--FILE--
+<?php
+
+$a = [null => 1];
+
+echo $a[null];
+
+?>
+--EXPECTF--
+Deprecated: Using null as an array offset is deprecated, use an empty string instead in %s on line %d
+
+Deprecated: Using null as an array offset is deprecated, use an empty string instead in %s on line %d
+1

Zend/zend_compile.c

@@ -10175,9 +10175,7 @@ static bool zend_try_ct_eval_array(zval *result, zend_ast *ast) /* {{{ */
 					zend_long lval = zend_dval_to_lval_silent(Z_DVAL_P(key));
 					/* Incompatible float will generate an error, leave this to run-time */
 					if (!zend_is_long_compatible(Z_DVAL_P(key), lval)) {
-						zval_ptr_dtor_nogc(value);
-						zval_ptr_dtor(result);
-						return 0;
+						goto fail;
 					}
 					zend_hash_index_update(Z_ARRVAL_P(result), lval, value);
 					break;
@@ -10189,13 +10187,14 @@ static bool zend_try_ct_eval_array(zval *result, zend_ast *ast) /* {{{ */
 					zend_hash_index_update(Z_ARRVAL_P(result), 1, value);
 					break;
 				case IS_NULL:
-					zend_hash_update(Z_ARRVAL_P(result), ZSTR_EMPTY_ALLOC(), value);
-					break;
+					/* Null key will generate a warning at run-time. */
+					goto fail;
 				default:
 					zend_error_noreturn(E_COMPILE_ERROR, "Illegal offset type");
 					break;
 			}
 		} else if (!zend_hash_next_index_insert(Z_ARRVAL_P(result), value)) {
+fail:
 			zval_ptr_dtor_nogc(value);
 			zval_ptr_dtor(result);
 			return 0;

Zend/zend_vm_def.h

@@ -6278,7 +6278,11 @@ ZEND_VM_C_LABEL(num_index):
 		} else if ((OP2_TYPE & (IS_VAR|IS_CV)) && EXPECTED(Z_TYPE_P(offset) == IS_REFERENCE)) {
 			offset = Z_REFVAL_P(offset);
 			ZEND_VM_C_GOTO(add_again);
-		} else if (Z_TYPE_P(offset) == IS_NULL) {
+		} else if (UNEXPECTED(Z_TYPE_P(offset) == IS_NULL)) {
+			zend_error(E_DEPRECATED, "Using null as an array offset is deprecated, use an empty string instead");
+			if (UNEXPECTED(EG(exception))) {
+				HANDLE_EXCEPTION();
+			}
 			str = ZSTR_EMPTY_ALLOC();
 			ZEND_VM_C_GOTO(str_index);
 		} else if (Z_TYPE_P(offset) == IS_DOUBLE) {