Use scoped enums in C++ and flatbuffers. (#2194)

* Enable --scoped-enums in flatbuffer compiler.

* Change enum to c++11 style (enum class).

* Resolve conflicts.

* Solve building failure when RAY_USE_NEW_GCS=on and remove ERROR_INDEX suffix.

* Merge with master and fix CI failure.

src/common/state/error_table.h

@@ -4,12 +4,26 @@
 #include "db.h"
 #include "table.h"
 
+/// An ErrorIndex may be used as an index into error_types.
+enum class ErrorIndex : int32_t {
+  /// An object was added with a different hash from the existing one.
+  OBJECT_HASH_MISMATCH = 0,
+  /// An object that was created through a ray.put is lost.
+  PUT_RECONSTRUCTION,
+  /// A worker died or was killed while executing a task.
+  WORKER_DIED,
+  /// An actor hasn't been created for a while.
+  ACTOR_NOT_CREATED,
+  /// The total number of error types.
+  MAX
+};
+
 /// Data that is needed to push an error.
 typedef struct {
   /// The ID of the driver to push the error to.
   DBClientID driver_id;
   /// An index into the error_types array indicating the type of the error.
-  int error_type;
+  ErrorIndex error_type;
   /// The key to use for the error message in Redis.
   UniqueID error_key;
   /// The length of the error message.
@@ -18,20 +32,6 @@ typedef struct {
   uint8_t error_message[0];
 } ErrorInfo;
 
-/// An error_index may be used as an index into error_types.
-typedef enum {
-  /// An object was added with a different hash from the existing one.
-  OBJECT_HASH_MISMATCH_ERROR_INDEX = 0,
-  /// An object that was created through a ray.put is lost.
-  PUT_RECONSTRUCTION_ERROR_INDEX,
-  /// A worker died or was killed while executing a task.
-  WORKER_DIED_ERROR_INDEX,
-  /// An actor hasn't been created for a while.
-  ACTOR_NOT_CREATED_ERROR_INDEX,
-  /// The total number of error types.
-  MAX_ERROR_INDEX
-} error_index;
-
 extern const char *error_types[];
 
 /// Push an error to the given Python driver.
@@ -39,12 +39,12 @@ extern const char *error_types[];
 /// \param db_handle Database handle.
 /// \param driver_id The ID of the Python driver to push the error to.
 /// \param error_type An index specifying the type of the error. This should
-/// be a value from the error_index enum.
+/// be a value from the ErrorIndex enum.
 /// \param error_message The error message to print.
 /// \return Void.
 void push_error(DBHandle *db_handle,
                 DBClientID driver_id,
-                int error_type,
+                ErrorIndex error_type,
                 const std::string &error_message);
 
 #endif