Bug #20908: Crash if select @@""

Zero-length variables caused failures when using the length to look
up the name in a hash.  Instead, signal that no zero-length name can
ever be found and that to encounter one is a syntax error.


mysql-test/r/variables.result:
  Results for test.
mysql-test/t/variables.test:
  Insert tests to prove that zero-length variable names do not cause
  faults.
sql/gen_lex_hash.cc:
  If the length is zero, then there is nothing to look-up in the 
  hash.
sql/sql_lex.cc:
  Names of variables must not be empty.  Signal an error of that 
  happens.

1 files changed, 6 insertions, 0 deletions

diff --git a/mysql-test/r/variables.result b/mysql-test/r/variables.result
index a0e516d2397..cd834a789bd 100644
--- a/mysql-test/r/variables.result
+++ b/mysql-test/r/variables.result
@@ -689,6 +689,12 @@ select @@log_queries_not_using_indexes;
 show variables like 'log_queries_not_using_indexes';
 Variable_name	Value
 log_queries_not_using_indexes	OFF
+select @@"";
+ERROR 42000: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '""' at line 1
+select @@&;
+ERROR 42000: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '&' at line 1
+select @@@;
+ERROR 42000: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '@' at line 1
 End of 5.0 tests
 set global binlog_cache_size         =@my_binlog_cache_size;
 set global connect_timeout           =@my_connect_timeout;