Bugs#20392: INSERT_ID session variable has weird value

sys_var_insert_id returned LAST_INSERT_ID instead of INSERT_ID.

mysql-test/r/variables.result

@@ -421,6 +421,18 @@ set tmp_table_size=100;
 set tx_isolation="READ-COMMITTED";
 set wait_timeout=100;
 set log_warnings=1;
+select @@session.insert_id;
+@@session.insert_id
+1
+set @save_insert_id=@@session.insert_id;
+set session insert_id=20;
+select @@session.insert_id;
+@@session.insert_id
+20
+set @@session.insert_id=@save_insert_id;
+select @@session.insert_id;
+@@session.insert_id
+1
 create table t1 (a int not null auto_increment, primary key(a));
 create table t2 (a int not null auto_increment, primary key(a));
 insert into t1 values(null),(null),(null);

mysql-test/t/variables.test

@@ -301,6 +301,16 @@ set tx_isolation="READ-COMMITTED";
 set wait_timeout=100;
 set log_warnings=1;
 
+#
+# Bugs: #20392: INSERT_ID session variable has weird value
+#
+select @@session.insert_id;
+set @save_insert_id=@@session.insert_id;
+set session insert_id=20;
+select @@session.insert_id;
+set @@session.insert_id=@save_insert_id;
+select @@session.insert_id;
+
 #
 # key buffer
 #

sql/set_var.cc

@@ -2578,7 +2578,7 @@ bool sys_var_insert_id::update(THD *thd, set_var *var)
 byte *sys_var_insert_id::value_ptr(THD *thd, enum_var_type type,
 				   LEX_STRING *base)
 {
-  return (byte*) &thd->current_insert_id;
+  return (byte*) &thd->next_insert_id;
 }