conditionally adding mixed return type

With guidance from Remi Collet, use ZEND_BEGIN_ARG_WITH_TENTATIVE_RETURN_TYPE_EX macro, and use a conditional to fake that macro
for earlier php versions. Tested on 8.1 and 7.4, and deprecation notices gone plus all tests pass

php/ext/google/protobuf/array.c

@@ -309,7 +309,7 @@ PHP_METHOD(RepeatedField, offsetExists) {
 }
 
 /**
- * RepeatedField::offsetGet()
+ * RepeatedField::offsetGet(): mixed
  *
  * Implements the ArrayAccess interface. Invoked when PHP code calls:
  *
@@ -459,7 +459,7 @@ ZEND_BEGIN_ARG_INFO_EX(arginfo_append, 0, 0, 1)
   ZEND_ARG_INFO(0, newval)
 ZEND_END_ARG_INFO()
 
-ZEND_BEGIN_ARG_INFO_EX(arginfo_offsetGet, 0, 0, 1)
+ZEND_BEGIN_ARG_WITH_TENTATIVE_RETURN_TYPE_INFO_EX(arginfo_offsetGet, 0, 0, IS_MIXED, 1)
   ZEND_ARG_INFO(0, index)
 ZEND_END_ARG_INFO()
 
@@ -575,7 +575,7 @@ PHP_METHOD(RepeatedFieldIter, rewind) {
 }
 
 /**
- * RepeatedFieldIter::current()
+ * RepeatedFieldIter::current(): mixed
  *
  * Implements the Iterator interface. Returns the current value.
  */
@@ -598,7 +598,7 @@ PHP_METHOD(RepeatedFieldIter, current) {
 }
 
 /**
- * RepeatedFieldIter::key()
+ * RepeatedFieldIter::key(): mixed
  *
  * Implements the Iterator interface. Returns the current key.
  */
@@ -628,6 +628,12 @@ PHP_METHOD(RepeatedFieldIter, valid) {
   RETURN_BOOL(intern->position < upb_array_size(field->array));
 }
 
+ZEND_BEGIN_ARG_WITH_TENTATIVE_RETURN_TYPE_INFO_EX(arginfo_current, 0, 0, IS_MIXED, 0)
+ZEND_END_ARG_INFO()
+
+ZEND_BEGIN_ARG_WITH_TENTATIVE_RETURN_TYPE_INFO_EX(arginfo_key, 0, 0, IS_MIXED, 0)
+ZEND_END_ARG_INFO()
+
 ZEND_BEGIN_ARG_WITH_RETURN_TYPE_INFO_EX(arginfo_next, 0, 0, IS_VOID, 0)
 ZEND_END_ARG_INFO()
 
@@ -639,8 +645,8 @@ ZEND_END_ARG_INFO()
 
 static zend_function_entry repeated_field_iter_methods[] = {
   PHP_ME(RepeatedFieldIter, rewind,      arginfo_rewind, ZEND_ACC_PUBLIC)
-  PHP_ME(RepeatedFieldIter, current,     arginfo_void,   ZEND_ACC_PUBLIC)
-  PHP_ME(RepeatedFieldIter, key,         arginfo_void,   ZEND_ACC_PUBLIC)
+  PHP_ME(RepeatedFieldIter, current,     arginfo_current,   ZEND_ACC_PUBLIC)
+  PHP_ME(RepeatedFieldIter, key,         arginfo_key,   ZEND_ACC_PUBLIC)
   PHP_ME(RepeatedFieldIter, next,        arginfo_next,   ZEND_ACC_PUBLIC)
   PHP_ME(RepeatedFieldIter, valid,       arginfo_valid,  ZEND_ACC_PUBLIC)
   ZEND_FE_END

php/ext/google/protobuf/map.c

@@ -329,7 +329,7 @@ PHP_METHOD(MapField, offsetExists) {
 }
 
 /**
- * MapField::offsetGet()
+ * MapField::offsetGet(): mixed
  *
  * Implements the ArrayAccess interface. Invoked when PHP code calls:
  *
@@ -453,7 +453,8 @@ ZEND_BEGIN_ARG_INFO_EX(arginfo_construct, 0, 0, 2)
   ZEND_ARG_INFO(0, value_class)
 ZEND_END_ARG_INFO()
 
-ZEND_BEGIN_ARG_INFO_EX(arginfo_offsetGet, 0, 0, 1)
+
+ZEND_BEGIN_ARG_WITH_TENTATIVE_RETURN_TYPE_INFO_EX(arginfo_offsetGet, 0, 0, IS_MIXED, 1)
   ZEND_ARG_INFO(0, index)
 ZEND_END_ARG_INFO()
 
@@ -573,7 +574,7 @@ PHP_METHOD(MapFieldIter, rewind) {
 }
 
 /**
- * MapFieldIter::current()
+ * MapFieldIter::current(): mixed
  *
  * Implements the Iterator interface. Returns the current value.
  */
@@ -626,6 +627,12 @@ PHP_METHOD(MapFieldIter, valid) {
 ZEND_BEGIN_ARG_WITH_RETURN_TYPE_INFO_EX(arginfo_rewind, 0, 0, IS_VOID, 0)
 ZEND_END_ARG_INFO()
 
+ZEND_BEGIN_ARG_WITH_TENTATIVE_RETURN_TYPE_INFO_EX(arginfo_current, 0, 0, IS_MIXED, 0)
+ZEND_END_ARG_INFO()
+
+ZEND_BEGIN_ARG_WITH_TENTATIVE_RETURN_TYPE_INFO_EX(arginfo_key, 0, 0, IS_MIXED, 0)
+ZEND_END_ARG_INFO()
+
 ZEND_BEGIN_ARG_WITH_RETURN_TYPE_INFO_EX(arginfo_next, 0, 0, IS_VOID, 0)
 ZEND_END_ARG_INFO()
 
@@ -634,8 +641,8 @@ ZEND_END_ARG_INFO()
 
 static zend_function_entry map_field_iter_methods[] = {
   PHP_ME(MapFieldIter, rewind,      arginfo_rewind, ZEND_ACC_PUBLIC)
-  PHP_ME(MapFieldIter, current,     arginfo_void,   ZEND_ACC_PUBLIC)
-  PHP_ME(MapFieldIter, key,         arginfo_void,   ZEND_ACC_PUBLIC)
+  PHP_ME(MapFieldIter, current,     arginfo_current,   ZEND_ACC_PUBLIC)
+  PHP_ME(MapFieldIter, key,         arginfo_key,   ZEND_ACC_PUBLIC)
   PHP_ME(MapFieldIter, next,        arginfo_next,   ZEND_ACC_PUBLIC)
   PHP_ME(MapFieldIter, valid,       arginfo_valid,  ZEND_ACC_PUBLIC)
   ZEND_FE_END

php/ext/google/protobuf/protobuf.h

@@ -84,6 +84,16 @@ const zval *get_generated_pool();
 #define zend_ce_countable spl_ce_Countable
 #endif
 
+// In PHP 8.1, mismatched tentative return types emit a depracation notice.
+// https://wiki.php.net/rfc/internal_method_return_types
+//
+// When compiling for earlier php versions, the return type is dropped.
+#if PHP_VERSION_ID < 80100
+#define ZEND_BEGIN_ARG_WITH_TENTATIVE_RETURN_TYPE_INFO_EX(name, return_reference, required_num_args, type, allow_null) \
+        ZEND_BEGIN_ARG_INFO_EX(name, return_reference, required_num_args, allow_null)
+#define IS_MIXED 16
+#endif
+
 ZEND_BEGIN_ARG_INFO(arginfo_void, 0)
 ZEND_END_ARG_INFO()