BUG#47027 delegates_init() failure is not user friendly (usability issue)

      
Function delegetas_init() did not report proper error messages
when there are failures, which made it hard to know where the problem
occurred.

Fixed the problem by adding specific error message for every possible
place that can fail. And since these failures are supposed to never
happen, ask the user to report a bug if they happened.

sql/mysqld.cc

@@ -3778,12 +3778,12 @@ static int init_server_components()
     unireg_abort(1);
   }
 
-  /* initialize delegates for extension observers */
+  /*
+    initialize delegates for extension observers, errors have already
+    been reported in the function
+  */
   if (delegates_init())
-  {
-    sql_print_error("Initialize extension delegates failed");
     unireg_abort(1);
-  }
 
   /* need to configure logging before initializing storage engines */
   if (opt_log_slave_updates && !opt_bin_log)

sql/rpl_handler.cc

@@ -105,12 +105,20 @@ int delegates_init()
   transaction_delegate= new (place_trans_mem) Trans_delegate;
 
   if (!transaction_delegate->is_inited())
+  {
+    sql_print_error("Initialization of transaction delegates failed. "
+                    "Please report a bug.");
     return 1;
+  }
 
   binlog_storage_delegate= new (place_storage_mem) Binlog_storage_delegate;
 
   if (!binlog_storage_delegate->is_inited())
+  {
+    sql_print_error("Initialization binlog storage delegates failed. "
+                    "Please report a bug.");
     return 1;
+  }
 
 #ifdef HAVE_REPLICATION
   void *place_transmit_mem= transmit_mem.data;
@@ -119,16 +127,29 @@ int delegates_init()
   binlog_transmit_delegate= new (place_transmit_mem) Binlog_transmit_delegate;
 
   if (!binlog_transmit_delegate->is_inited())
+  {
+    sql_print_error("Initialization of binlog transmit delegates failed. "
+                    "Please report a bug.");
     return 1;
+  }
 
   binlog_relay_io_delegate= new (place_relay_io_mem) Binlog_relay_IO_delegate;
 
   if (!binlog_relay_io_delegate->is_inited())
+  {
+    sql_print_error("Initialization binlog relay IO delegates failed. "
+                    "Please report a bug.");
     return 1;
+  }
 #endif
 
   if (pthread_key_create(&RPL_TRANS_BINLOG_INFO, NULL))
+  {
+    sql_print_error("Error while creating pthread specific data key for replication. "
+                    "Please report a bug.");
     return 1;
+  }
+
   return 0;
 }