Bug#37631 Incorrect key file for table after upgrading from 5.0 to 5.1

The conformance checker was not taking into
account, and, making concessions for acceptable
incompatibilites in tables created by
versions earlier than 4.1.

The current patch relaxes the conformance
checker to ignore differences in key_alg
and language for tables created by versions
earlier than 4.1.

storage/myisam/ha_myisam.cc:
  Modify check_definition to ignore differences
  in key_alg and language for tables created
  by versions earlier than 4.1.

storage/myisam/ha_myisam.cc

@@ -315,6 +315,7 @@ int table2myisam(TABLE *table_arg, MI_KEYDEF **keydef_out,
       t2_keys          in    Number of keys in second table
       t2_recs          in    Number of records in second table
       strict           in    Strict check switch
+      table            in    handle to the table object
 
   DESCRIPTION
     This function compares two MyISAM definitions. By intention it was done
@@ -330,6 +331,10 @@ int table2myisam(TABLE *table_arg, MI_KEYDEF **keydef_out,
     Otherwise 'strict' flag must be set to 1 and it is not required to pass
     converted dot-frm definition as t1_*.
 
+    For compatibility reasons we relax some checks, specifically:
+    - 4.0 (and earlier versions) always set key_alg to 0.
+    - 4.0 (and earlier versions) have the same language for all keysegs.
+
   RETURN VALUE
     0 - Equal definitions.
     1 - Different definitions.
@@ -344,10 +349,11 @@ int table2myisam(TABLE *table_arg, MI_KEYDEF **keydef_out,
 int check_definition(MI_KEYDEF *t1_keyinfo, MI_COLUMNDEF *t1_recinfo,
                      uint t1_keys, uint t1_recs,
                      MI_KEYDEF *t2_keyinfo, MI_COLUMNDEF *t2_recinfo,
-                     uint t2_keys, uint t2_recs, bool strict)
+                     uint t2_keys, uint t2_recs, bool strict, TABLE *table_arg)
 {
   uint i, j;
   DBUG_ENTER("check_definition");
+  my_bool mysql_40_compat= table_arg && table_arg->s->frm_version < FRM_VER_TRUE_VARCHAR;
   if ((strict ? t1_keys != t2_keys : t1_keys > t2_keys))
   {
     DBUG_PRINT("error", ("Number of keys differs: t1_keys=%u, t2_keys=%u",
@@ -386,8 +392,9 @@ int check_definition(MI_KEYDEF *t1_keyinfo, MI_COLUMNDEF *t1_recinfo,
                             test(t2_keyinfo[i].flag & HA_SPATIAL)));
        DBUG_RETURN(1);
     }
-    if (t1_keyinfo[i].keysegs != t2_keyinfo[i].keysegs ||
-        t1_keyinfo[i].key_alg != t2_keyinfo[i].key_alg)
+    if ((mysql_40_compat &&
+        t1_keyinfo[i].key_alg != t2_keyinfo[i].key_alg) ||
+        t1_keyinfo[i].keysegs != t2_keyinfo[i].keysegs)
     {
       DBUG_PRINT("error", ("Key %d has different definition", i));
       DBUG_PRINT("error", ("t1_keysegs=%d, t1_key_alg=%d",
@@ -417,8 +424,9 @@ int check_definition(MI_KEYDEF *t1_keyinfo, MI_COLUMNDEF *t1_recinfo,
           t1_keysegs_j__type= HA_KEYTYPE_VARBINARY1; /* purecov: inspected */
       }
 
-      if (t1_keysegs_j__type != t2_keysegs[j].type ||
-          t1_keysegs[j].language != t2_keysegs[j].language ||
+      if ((mysql_40_compat &&
+          t1_keysegs[j].language != t2_keysegs[j].language) ||
+          t1_keysegs_j__type != t2_keysegs[j].type ||
           t1_keysegs[j].null_bit != t2_keysegs[j].null_bit ||
           t1_keysegs[j].length != t2_keysegs[j].length)
       {
@@ -671,7 +679,8 @@ int ha_myisam::open(const char *name, int mode, uint test_if_locked)
     }
     if (check_definition(keyinfo, recinfo, table->s->keys, recs,
                          file->s->keyinfo, file->s->rec,
-                         file->s->base.keys, file->s->base.fields, true))
+                         file->s->base.keys, file->s->base.fields,
+                         true, table))
     {
       /* purecov: begin inspected */
       my_errno= HA_ERR_CRASHED;

storage/myisammrg/ha_myisammrg.cc

@@ -137,7 +137,8 @@ extern int table2myisam(TABLE *table_arg, MI_KEYDEF **keydef_out,
 extern int check_definition(MI_KEYDEF *t1_keyinfo, MI_COLUMNDEF *t1_recinfo,
                             uint t1_keys, uint t1_recs,
                             MI_KEYDEF *t2_keyinfo, MI_COLUMNDEF *t2_recinfo,
-                            uint t2_keys, uint t2_recs, bool strict);
+                            uint t2_keys, uint t2_recs, bool strict,
+                            TABLE *table_arg);
 static void split_file_name(const char *file_name,
 			    LEX_STRING *db, LEX_STRING *name);
 
@@ -595,7 +596,7 @@ int ha_myisammrg::attach_children(void)
       if (check_definition(keyinfo, recinfo, keys, recs,
                            u_table->table->s->keyinfo, u_table->table->s->rec,
                            u_table->table->s->base.keys,
-                           u_table->table->s->base.fields, false))
+                           u_table->table->s->base.fields, false, NULL))
       {
         DBUG_PRINT("error", ("table definition mismatch: '%s'",
                              u_table->table->filename));