MDEV-32012 hash unique corrupts index on virtual blobs

as always when copying record[0] aside one needs to detach
Field_blob::value's from it, and restore them when record[0]
is restored from a backup.

mysql-test/main/long_unique_bugs.result

@@ -454,5 +454,29 @@ create table t1 (f text not null, unique (f));
 insert into t1 (f) select 'f';
 drop table t1;
 #
+# MDEV-32012 hash unique corrupts index on virtual blobs
+#
+create table t1 (
+f1 varchar(25),
+v1 mediumtext generated always as (concat('f1:', f1)) virtual,
+unique key (f1) using hash,
+key (v1(1000))
+);
+flush status;
+insert ignore t1 (f1) values (9599),(94410);
+show status like 'handler_read_next';
+Variable_name	Value
+Handler_read_next	1
+# the above MUST BE =1
+check table t1 extended;
+Table	Op	Msg_type	Msg_text
+test.t1	check	status	OK
+update t1 set f1=100 where f1=9599;
+update t1 set f1=9599 where f1=100;
+check table t1 extended;
+Table	Op	Msg_type	Msg_text
+test.t1	check	status	OK
+drop table t1;
+#
 # End of 10.4 tests
 #

mysql-test/main/long_unique_bugs.test

@@ -455,6 +455,30 @@ create table t1 (f text not null, unique (f));
 insert into t1 (f) select 'f';
 drop table t1;
 
+--echo #
+--echo # MDEV-32012 hash unique corrupts index on virtual blobs
+--echo #
+create table t1 (
+  f1 varchar(25),
+  v1 mediumtext generated always as (concat('f1:', f1)) virtual,
+  unique key (f1) using hash,
+  key (v1(1000))
+);
+flush status;
+insert ignore t1 (f1) values (9599),(94410);
+# handler_read_next must be 1 below, meaning there was a hash collision above.
+# if a change in the hash function causes these values not to collide anymore,
+# the test must be adjusted to use some other values that collide.
+# to find a collision add an assert into check_duplicate_long_entry_key()
+# and run, like, insert...select * seq_from_1_to_1000000000
+show status like 'handler_read_next';
+--echo # the above MUST BE =1
+check table t1 extended;
+update t1 set f1=100 where f1=9599;
+update t1 set f1=9599 where f1=100;
+check table t1 extended;
+drop table t1;
+
 --echo #
 --echo # End of 10.4 tests
 --echo #

sql/handler.cc

@@ -6658,6 +6658,7 @@ static int check_duplicate_long_entry_key(TABLE *table, handler *h,
   KEY *key_info= table->key_info + key_no;
   hash_field= key_info->key_part->field;
   uchar ptr[HA_HASH_KEY_LENGTH_WITH_NULL];
+  String *blob_storage;
 
   DBUG_ASSERT((key_info->flags & HA_NULL_PART_KEY &&
                key_info->key_length == HA_HASH_KEY_LENGTH_WITH_NULL)
@@ -6675,6 +6676,8 @@ static int check_duplicate_long_entry_key(TABLE *table, handler *h,
   result= h->ha_index_init(key_no, 0);
   if (result)
     return result;
+  blob_storage= (String*)alloca(sizeof(String)*table->s->virtual_not_stored_blob_fields);
+  table->remember_blob_values(blob_storage);
   store_record(table, check_unique_buf);
   result= h->ha_index_read_map(table->record[0],
                                ptr, HA_WHOLE_KEY, HA_READ_KEY_EXACT);
@@ -6685,6 +6688,13 @@ static int check_duplicate_long_entry_key(TABLE *table, handler *h,
     Item_func_hash * temp= (Item_func_hash *)hash_field->vcol_info->expr;
     Item ** arguments= temp->arguments();
     uint arg_count= temp->argument_count();
+    // restore pointers after swap_values in TABLE::update_virtual_fields()
+    for (Field **vf= table->vfield; *vf; vf++)
+    {
+      if (!(*vf)->stored_in_db() && (*vf)->flags & BLOB_FLAG &&
+          bitmap_is_set(table->read_set, (*vf)->field_index))
+        ((Field_blob*)*vf)->swap_value_and_read_value();
+    }
     do
     {
       my_ptrdiff_t diff= table->check_unique_buf - new_rec;
@@ -6731,6 +6741,7 @@ exit:
     }
   }
   restore_record(table, check_unique_buf);
+  table->restore_blob_values(blob_storage);
   h->ha_index_end();
   return error;
 }