Fix handling of "SET TRANSACTION ISOLATION LEVEL ...". (Bug #7955)

mysql-test/r/bdb.result:
  Add results
mysql-test/t/bdb.test:
  Add new test
sql/set_var.cc:
  Refuse attempts to change tx_isolation while a transaction is in progress.
sql/set_var.h:
  Support check function for sys_var_thd_enum
sql/share/errmsg.txt:
  Add new error message
sql/sql_yacc.yy:
  Make sure that lex->option_type always gets set in 'SET TRANSACTION ...'

mysql-test/r/bdb.result

@@ -1895,3 +1895,21 @@ t1	CREATE TABLE `t1` (
 ) ENGINE=BerkeleyDB DEFAULT CHARSET=latin1
 drop table t1;
 set storage_engine=MyISAM;
+create table t1 (a int) engine=bdb;
+set session transaction isolation level repeatable read;
+set transaction isolation level serializable;
+begin;
+select @@tx_isolation;
+@@tx_isolation
+SERIALIZABLE
+insert into t1 values (1);
+set transaction isolation level read committed;
+ERROR 25001: Transaction isolation level can't be changed while a transaction is in progress
+rollback;
+begin;
+select @@tx_isolation;
+@@tx_isolation
+REPEATABLE-READ
+insert into t1 values (1);
+rollback;
+drop table t1;

mysql-test/t/bdb.test

@@ -973,3 +973,24 @@ drop table t1;
 
 # End varchar test
 eval set storage_engine=$default;
+
+#
+# Bug #7955: SET TRANSACTION ISIOLATION LEVEL lives longer than next
+# transaciton
+#
+create table t1 (a int) engine=bdb;
+set session transaction isolation level repeatable read;
+set transaction isolation level serializable;
+begin;
+select @@tx_isolation;
+insert into t1 values (1);
+--error ER_CANT_CHANGE_TX_ISOLATION
+set transaction isolation level read committed;
+rollback;
+begin;
+select @@tx_isolation;
+insert into t1 values (1);
+rollback;
+drop table t1;
+
+# End of 5.0 tests

sql/set_var.cc

@@ -99,6 +99,7 @@ static bool set_log_update(THD *thd, set_var *var);
 static int  check_pseudo_thread_id(THD *thd, set_var *var);
 static bool set_log_bin(THD *thd, set_var *var);
 static void fix_low_priority_updates(THD *thd, enum_var_type type);
+static int check_tx_isolation(THD *thd, set_var *var);
 static void fix_tx_isolation(THD *thd, enum_var_type type);
 static int check_completion_type(THD *thd, set_var *var);
 static void fix_completion_type(THD *thd, enum_var_type type);
@@ -386,7 +387,8 @@ sys_var_long_ptr	sys_thread_cache_size("thread_cache_size",
 sys_var_thd_enum	sys_tx_isolation("tx_isolation",
 					 &SV::tx_isolation,
 					 &tx_isolation_typelib,
-					 fix_tx_isolation);
+					 fix_tx_isolation,
+					 check_tx_isolation);
 sys_var_thd_ulong	sys_tmp_table_size("tmp_table_size",
 					   &SV::tmp_table_size);
 sys_var_bool_ptr  sys_timed_mutexes("timed_mutexes",
@@ -1163,11 +1165,24 @@ static void fix_max_join_size(THD *thd, enum_var_type type)
 }
 
 
+/*
+  Can't change the 'next' tx_isolation while we are already in
+  a transaction
+*/
+static int check_tx_isolation(THD *thd, set_var *var)
+{
+  if (var->type == OPT_DEFAULT && (thd->server_status & SERVER_STATUS_IN_TRANS))
+  {
+    my_error(ER_CANT_CHANGE_TX_ISOLATION, MYF(0));
+    return 1;
+  }
+  return 0;
+}
+
 /*
   If one doesn't use the SESSION modifier, the isolation level
   is only active for the next command
 */
-
 static void fix_tx_isolation(THD *thd, enum_var_type type)
 {
   if (type == OPT_SESSION)

sql/set_var.h

@@ -325,19 +325,31 @@ class sys_var_thd_enum :public sys_var_thd
 protected:
   ulong SV::*offset;
   TYPELIB *enum_names;
+  sys_check_func check_func;
 public:
   sys_var_thd_enum(const char *name_arg, ulong SV::*offset_arg,
 		   TYPELIB *typelib)
-    :sys_var_thd(name_arg), offset(offset_arg), enum_names(typelib)
+    :sys_var_thd(name_arg), offset(offset_arg), enum_names(typelib),
+    check_func(0)
   {}
   sys_var_thd_enum(const char *name_arg, ulong SV::*offset_arg,
 		   TYPELIB *typelib,
 		   sys_after_update_func func)
-    :sys_var_thd(name_arg,func), offset(offset_arg), enum_names(typelib)
+    :sys_var_thd(name_arg,func), offset(offset_arg), enum_names(typelib),
+    check_func(0)
+  {}
+  sys_var_thd_enum(const char *name_arg, ulong SV::*offset_arg,
+		   TYPELIB *typelib, sys_after_update_func func,
+                   sys_check_func check)
+    :sys_var_thd(name_arg,func), offset(offset_arg), enum_names(typelib),
+    check_func(check)
   {}
   bool check(THD *thd, set_var *var)
   {
-    return check_enum(thd, var, enum_names);
+    int ret= 0;
+    if (check_func)
+      ret= (*check_func)(thd, var);
+    return ret ? ret : check_enum(thd, var, enum_names);
   }
   bool update(THD *thd, set_var *var);
   void set_default(THD *thd, enum_var_type type);

sql/share/errmsg.txt

@@ -5421,3 +5421,5 @@ ER_NO_REFERENCED_ROW_2 23000
 	eng "Cannot add or update a child row: a foreign key constraint fails (%.192s)"
 ER_SP_BAD_VAR_SHADOW 42000
 	eng "Variable '%-.64s' must be quoted with `...`, or renamed"
+ER_CANT_CHANGE_TX_ISOLATION 25001
+	eng "Transaction isolation level can't be changed while a transaction is in progress"

sql/sql_yacc.yy

@@ -8002,8 +8002,7 @@ sys_option_value:
         | option_type TRANSACTION_SYM ISOLATION LEVEL_SYM isolation_types
 	{
 	  LEX *lex=Lex;
-          if ($1)
-            lex->option_type= $1;
+	  lex->option_type= $1;
 	  lex->var_list.push_back(new set_var(lex->option_type,
                                               find_sys_var("tx_isolation"),
                                               &null_lex_str,