Bug#42364 SHOW ERRORS returns empty resultset after dropping non existent table

partial backport of bug43138 fix

mysql-test/r/warnings.result

@@ -313,4 +313,9 @@ ERROR 22001: Data too long for column 'c_tinytext' at row 1
 insert into t2 values(@q);
 ERROR 22001: Data too long for column 'c_tinyblob' at row 1
 drop table t1, t2;
+DROP TABLE t1;
+ERROR 42S02: Unknown table 't1'
+SHOW ERRORS;
+Level	Code	Message
+Error	1051	Unknown table 't1'
 End of 5.0 tests

mysql-test/t/warnings.test

@@ -225,4 +225,11 @@ insert into t2 values(@q);
 
 drop table t1, t2;
 
+#
+# Bug#42364 SHOW ERRORS returns empty resultset after dropping non existent table
+#
+--error ER_BAD_TABLE_ERROR
+DROP TABLE t1;
+SHOW ERRORS;
+
 --echo End of 5.0 tests

sql/sql_class.cc

@@ -399,6 +399,31 @@ char *thd_security_context(THD *thd, char *buffer, unsigned int length,
   return buffer;
 }
 
+
+/**
+  Implementation of Drop_table_error_handler::handle_error().
+  The reason in having this implementation is to silence technical low-level
+  warnings during DROP TABLE operation. Currently we don't want to expose
+  the following warnings during DROP TABLE:
+    - Some of table files are missed or invalid (the table is going to be
+      deleted anyway, so why bother that something was missed);
+    - A trigger associated with the table does not have DEFINER (One of the
+      MySQL specifics now is that triggers are loaded for the table being
+      dropped. So, we may have a warning that trigger does not have DEFINER
+      attribute during DROP TABLE operation).
+
+  @return TRUE if the condition is handled.
+*/
+bool Drop_table_error_handler::handle_error(uint sql_errno,
+                                            const char *message,
+                                            MYSQL_ERROR::enum_warning_level level,
+                                            THD *thd)
+{
+  return ((sql_errno == EE_DELETE && my_errno == ENOENT) ||
+          sql_errno == ER_TRG_NO_DEFINER);
+}
+
+
 /**
   Clear this diagnostics area. 
 

sql/sql_class.h

@@ -1091,6 +1091,31 @@ public:
 };
 
 
+/**
+  This class is an internal error handler implementation for 
+  DROP TABLE statements. The thing is that there may be warnings during
+  execution of these statements, which should not be exposed to the user.
+  This class is intended to silence such warnings.
+*/
+
+class Drop_table_error_handler : public Internal_error_handler
+{
+public:
+  Drop_table_error_handler(Internal_error_handler *err_handler)
+    :m_err_handler(err_handler)
+  { }
+
+public:
+  bool handle_error(uint sql_errno,
+                    const char *message,
+                    MYSQL_ERROR::enum_warning_level level,
+                    THD *thd);
+
+private:
+  Internal_error_handler *m_err_handler;
+};
+
+
 /**
   Stores status of the currently executed statement.
   Cleared at the beginning of the statement, and then

sql/sql_table.cc

@@ -1772,6 +1772,7 @@ bool mysql_rm_table(THD *thd,TABLE_LIST *tables, my_bool if_exists,
                     my_bool drop_temporary)
 {
   bool error= FALSE, need_start_waiters= FALSE;
+  Drop_table_error_handler err_handler(thd->get_internal_handler());
   DBUG_ENTER("mysql_rm_table");
 
   /* mark for close and remove all cached entries */
@@ -1792,7 +1793,10 @@ bool mysql_rm_table(THD *thd,TABLE_LIST *tables, my_bool if_exists,
     LOCK_open during wait_if_global_read_lock(), other threads could not
     close their tables. This would make a pretty deadlock.
   */
+  thd->push_internal_handler(&err_handler);
   error= mysql_rm_table_part2(thd, tables, if_exists, drop_temporary, 0, 0);
+  thd->pop_internal_handler();
+
 
   if (need_start_waiters)
     start_waiting_global_read_lock(thd);
@@ -1894,9 +1898,6 @@ int mysql_rm_table_part2(THD *thd, TABLE_LIST *tables, bool if_exists,
     DBUG_RETURN(1);
   }
 
-  /* Don't give warnings for not found errors, as we already generate notes */
-  thd->no_warnings_for_error= 1;
-
   for (table= tables; table; table= table->next_local)
   {
     char *db=table->db;
@@ -2145,7 +2146,6 @@ int mysql_rm_table_part2(THD *thd, TABLE_LIST *tables, bool if_exists,
 err_with_placeholders:
   unlock_table_names(thd, tables, (TABLE_LIST*) 0);
   pthread_mutex_unlock(&LOCK_open);
-  thd->no_warnings_for_error= 0;
   DBUG_RETURN(error);
 }