MDEV-340 Save replication comments for DROP TABLE.

      mysql_rm_table_no_locks() function was modified.
      When we construct log record for the DROP TABLE, now we
      look if there's a comment before the first table name and
      add it to the record if so.
  
per-file comments:
  sql/sql_table.cc
  MDEV-340 Save replication comments for DROP TABLE.
        comment_length() function implemented to find comments in the query,
        call it in mysql_rm_table_no_locks() and use the result to form log record.
  mysql-test/suite/binlog/r/binlog_drop_if_exists.result
  MDEV-340 Save replication comments for DROP TABLE.
        test result updated.
  mysql-test/suite/binlog/t/binlog_drop_if_exists.test
  MDEV-340 Save replication comments for DROP TABLE.
        test case added.

mysql-test/suite/binlog/r/binlog_drop_if_exists.result

@@ -96,3 +96,21 @@ master-bin.000001	#	Query	#	#	use `test`; DROP VIEW IF EXISTS db_bug_13684.v
 master-bin.000001	#	Query	#	#	use `test`; DROP EVENT IF EXISTS db_bug_13684.e
 master-bin.000001	#	Query	#	#	use `test`; DROP TABLE IF EXISTS `db_bug_13684`.`t` /* generated by server */
 master-bin.000001	#	Query	#	#	DROP DATABASE IF EXISTS db_bug_13684
+CREATE TABLE t1(id int);
+DROP TABLE /* comment */ t1;
+CREATE TABLE t1(id int);
+DROP TABLE IF EXISTS /* comment */ t1;
+CREATE TABLE t1(id int);
+DROP TABLE /**/ t1;
+CREATE TABLE t1(id int);
+DROP TABLE IF EXISTS /* */ t1;
+show binlog events from <binlog_start>;
+Log_name	Pos	Event_type	Server_id	End_log_pos	Info
+master-bin.000001	#	Query	#	#	use `test`; CREATE TABLE t1(id int)
+master-bin.000001	#	Query	#	#	use `test`; DROP TABLE /* comment */ `t1` /* generated by server */
+master-bin.000001	#	Query	#	#	use `test`; CREATE TABLE t1(id int)
+master-bin.000001	#	Query	#	#	use `test`; DROP TABLE IF EXISTS /* comment */ `t1` /* generated by server */
+master-bin.000001	#	Query	#	#	use `test`; CREATE TABLE t1(id int)
+master-bin.000001	#	Query	#	#	use `test`; DROP TABLE /**/ `t1` /* generated by server */
+master-bin.000001	#	Query	#	#	use `test`; CREATE TABLE t1(id int)
+master-bin.000001	#	Query	#	#	use `test`; DROP TABLE IF EXISTS /* */ `t1` /* generated by server */

mysql-test/suite/binlog/t/binlog_drop_if_exists.test

@@ -113,3 +113,18 @@ if($fixed_bug_25705)
 --source include/show_binlog_events.inc
 
 enable_warnings;
+
+# Drop comments in binlog
+let $binlog_start= query_get_value(SHOW MASTER STATUS, Position, 1);
+CREATE TABLE t1(id int);
+DROP TABLE /* comment */ t1;
+CREATE TABLE t1(id int);
+DROP TABLE IF EXISTS /* comment */ t1;
+
+CREATE TABLE t1(id int);
+DROP TABLE /**/ t1;
+CREATE TABLE t1(id int);
+DROP TABLE IF EXISTS /* */ t1;
+
+--source include/show_binlog_events.inc
+

sql/sql_table.cc

@@ -1943,6 +1943,49 @@ bool mysql_rm_table(THD *thd,TABLE_LIST *tables, my_bool if_exists,
 }
 
 
+/**
+  Find the comment in the query.
+  That's auxiliary function to be used handling DROP TABLE [comment].
+
+  @param  thd             Thread handler
+  @param  comment_pos     How many characters to skip before the comment.
+                          Can be either 9 for DROP TABLE or
+                          17 for DROP TABLE IF EXISTS
+  @param  comment_start   returns the beginning of the comment if found.
+
+  @retval  0  no comment found
+  @retval  >0 the lenght of the comment found
+
+*/
+static uint32 comment_length(THD *thd, uint32 comment_pos,
+                             const char **comment_start)
+{
+  const char *query= thd->query();
+  const char *query_end= query + thd->query_length();
+  const uchar *const state_map= thd->charset()->state_map;
+
+  for (; query < query_end; query++)
+  {
+    if (state_map[*query] == MY_LEX_SKIP)
+      continue;
+    if (comment_pos-- == 0)
+      break;
+  }
+  if (query > query_end - 3 /* comment can't be shorter than 4 */ ||
+      state_map[*query] != MY_LEX_LONG_COMMENT || query[1] != '*')
+    return 0;
+  
+  *comment_start= query;
+  
+  for (query+= 3; query < query_end; query++)
+  {
+    if (query[-1] == '*' && query[0] == '/')
+      return query - *comment_start + 1;
+  }
+  return 0;
+}
+
+
 /**
   Execute the drop of a normal or temporary table.
 
@@ -2018,11 +2061,20 @@ int mysql_rm_table_no_locks(THD *thd, TABLE_LIST *tables, bool if_exists,
   {
     if (!drop_temporary)
     {
+      const char *comment_start;
+      uint32 comment_len;
+
       built_query.set_charset(system_charset_info);
       if (if_exists)
         built_query.append("DROP TABLE IF EXISTS ");
       else
         built_query.append("DROP TABLE ");
+
+      if ((comment_len= comment_length(thd, if_exists ? 17:9, &comment_start)))
+      {
+        built_query.append(comment_start, comment_len);
+        built_query.append(" ");
+      }
     }
 
     if (thd->is_current_stmt_binlog_format_row() || if_exists)