Add opcodes to zend_wrong_string_offset()

Zend/tests/string_offset_errors.phpt

@@ -0,0 +1,27 @@
+--TEST--
+Some string offset errors
+--FILE--
+<?php
+
+function &test() : string {
+    $str = "foo";
+    return $str[0];
+}
+
+try {
+    test();
+} catch (Error $e) {
+    echo $e->getMessage(), "\n";
+}
+
+try {
+    $str = "foo";
+    $str[0] =& $str[1];
+} catch (Error $e) {
+    echo $e->getMessage(), "\n";
+}
+
+?>
+--EXPECT--
+Cannot return string offsets by reference
+Cannot create references to/from string offsets

Zend/zend_execute.c

@@ -1262,9 +1262,11 @@ static zend_never_inline ZEND_COLD void zend_wrong_string_offset(void)
 						case ZEND_ASSIGN_REF:
 						case ZEND_ADD_ARRAY_ELEMENT:
 						case ZEND_INIT_ARRAY:
+						case ZEND_MAKE_REF:
 							msg = "Cannot create references to/from string offsets";
 							break;
 						case ZEND_RETURN_BY_REF:
+						case ZEND_VERIFY_RETURN_TYPE:
 							msg = "Cannot return string offsets by reference";
 							break;
 						case ZEND_UNSET_DIM:

ext/opcache/Optimizer/zend_inference.c

@@ -3229,6 +3229,7 @@ static void zend_update_type_info(const zend_op_array *op_array,
 						case ZEND_ADD_ARRAY_ELEMENT:
 						case ZEND_RETURN_BY_REF:
 						case ZEND_VERIFY_RETURN_TYPE:
+						case ZEND_MAKE_REF:
 							tmp |= MAY_BE_ARRAY_OF_ANY | MAY_BE_ARRAY_OF_REF;
 							break;
 						case ZEND_PRE_INC: