Bug#20922 mysql removes a name of first column in a table

0xFF is internal separator for SET|ENUM names. 
If this symbol is present in SET|ENUM names then we replace it with 
','(deprecated symbol for SET|ENUM names) during frm creation
and restore to 0xFF during frm opening

mysql-test/r/type_enum.result

@@ -1745,3 +1745,12 @@ create table t1 (a set('x','y') default 'x');
 alter table t1 alter a set default 'z';
 ERROR 42000: Invalid default value for 'a'
 drop table t1;
+create table t1 (f1 int);
+alter table t1 add f2 enum(0xFFFF);
+show create table t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `f1` int(11) default NULL,
+  `f2` enum('') default NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1
+drop table t1;

mysql-test/t/type_enum.test

@@ -127,4 +127,13 @@ create table t1 (a set('x','y') default 'x');
 alter table t1 alter a set default 'z';
 drop table t1;
 
+
+#
+# Bug#20922 mysql removes a name of first column in a table
+#
+create table t1 (f1 int);
+alter table t1 add f2 enum(0xFFFF);
+show create table t1;
+drop table t1;
+
 # End of 4.1 tests

sql/table.cc

@@ -387,7 +387,21 @@ int openfrm(const char *name, const char *alias, uint db_stat, uint prgflag,
                                                         count)))
         goto err_not_open;
       for (count= 0; count < interval->count; count++)
-        interval->type_lengths[count]= strlen(interval->type_names[count]);
+      {
+        char *val= (char*) interval->type_names[count];
+        interval->type_lengths[count]= strlen(val);
+        /*
+          Replace all ',' symbols with NAMES_SEP_CHAR.
+          See the comment in unireg.cc, pack_fields() function
+          for details.
+        */
+        for (uint cnt= 0 ; cnt < interval->type_lengths[count] ; cnt++)
+        {
+          char c= val[cnt];
+          if (c == ',')
+            val[cnt]= NAMES_SEP_CHAR;
+        }       
+      }
       interval->type_lengths[count]= 0;
     }
   }

sql/unireg.cc

@@ -637,6 +637,21 @@ static bool pack_fields(File file, List<create_field> &create_fields,
 	tmp.append(NAMES_SEP_CHAR);
 	for (const char **pos=field->interval->type_names ; *pos ; pos++)
 	{
+          char *val= (char*) *pos;
+          uint str_len= strlen(val);
+          /*
+            Note, hack: in old frm NAMES_SEP_CHAR is used to separate
+            names in the interval (ENUM/SET). To allow names to contain
+            NAMES_SEP_CHAR, we replace it with a comma before writing frm.
+            Backward conversion is done during frm file opening,
+            See table.cc, openfrm() function
+          */
+          for (uint cnt= 0 ; cnt < str_len ; cnt++)
+          {
+            char c= val[cnt];
+            if (c == NAMES_SEP_CHAR)
+              val[cnt]= ',';
+          }
 	  tmp.append(*pos);
 	  tmp.append(NAMES_SEP_CHAR);
 	}