MDEV-15620 Crash when using "SET @@NEW.a=expr" inside a trigger

The problem resided in this branch of the "option_value_no_option_type" rule:

| '@' '@' opt_var_ident_type internal_variable_name equal set_expr_or_default

Summary:

1. internal_variable_name initialized tmp.var to trg_new_row_fake_var (0x01).
2. The condition "if (tmp.var == NULL)" did not check
   the special case with trg_new_row_fake_var,
   so Lex->set_system_variable(&tmp, $3, $6) was
   called with tmp.var pointing to trg_new_row_fake_var,
   which created a sys_var instance pointing to 0x01 instead of
   a real system variable.
3. Later, at the trigger invocation time, this method was called:
   sys_var::do_deprecated_warning (this=0x1, thd=0x7ffe6c000a98)
   Notice, "this" is equal to trg_new_row_fake_var (0x01)

Solution:

The old implementation with separate rules
internal_variable_name (in sql_yacc.yy and sql_yacc_ora.yy) and
internal_variable_name_directly_assignable (in sql_yacc_ora.yy only)
was too complex and hard to follow.

Rewriting the code in a more straightforward way.

1. Changing LEX::set_system_variable()

from:

bool set_system_variable(struct sys_var_with_base *, enum_var_type, Item *);

to:

bool set_system_variable(enum_var_type, sys_var *, const LEX_CSTRING *, Item *);

2. Adding new methods in LEX, which operate with variable names:

bool set_trigger_field(const LEX_CSTRING *, const LEX_CSTRING *, Item *);
bool set_system_variable(enum_var_type var_type, const LEX_CSTRING *name,
                         Item *val);
bool set_system_variable(THD *thd, enum_var_type var_type,
                         const LEX_CSTRING *name1,
                         const LEX_CSTRING *name2,
                         Item *val);
bool set_default_system_variable(enum_var_type var_type,
                                 const LEX_CSTRING *name,
                                 Item *val);
bool set_variable(const LEX_CSTRING *name, Item *item);

3. Changing the grammar to call the new methods directly
   in option_value_no_option_type,
   Removing rules internal_variable_name and
   internal_variable_name_directly_assignable.

4. Removing "struct sys_var_with_base" and trg_new_row_fake_var.

Good side effect:

- The code in /sql reduced from 314 to 183 lines.
- MDEV-15615 Unexpected syntax error instead of "Unknown system variable" ...
  was also fixed automatically

4 files changed, 46 insertions, 4 deletions

diff --git a/mysql-test/suite/compat/oracle/r/func_misc.result b/mysql-test/suite/compat/oracle/r/func_misc.result
index 0e2ba0c6f50..f285423b446 100644
--- a/mysql-test/suite/compat/oracle/r/func_misc.result
+++ b/mysql-test/suite/compat/oracle/r/func_misc.result
@@ -35,7 +35,7 @@ CALL p1('SELECT 1');
 Error1: 0 normal, successful completition
 CALL p1('xxx');
 'Error2: ' || SQLCODE || ' ' || SQLERRM
-Error2: 1193 Unknown system variable 'xxx'
+Error2: 1064 You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near '' at line 1
 CALL p1('SELECT 1');
 1
 1
diff --git a/mysql-test/suite/compat/oracle/r/parser.result b/mysql-test/suite/compat/oracle/r/parser.result
new file mode 100644
index 00000000000..29588a68045
--- /dev/null
+++ b/mysql-test/suite/compat/oracle/r/parser.result
@@ -0,0 +1,18 @@
+SET sql_mode=ORACLE;
+#
+# MDEV-15620 Crash when using "SET @@NEW.a=expr" inside a trigger
+#
+CREATE TABLE t1 (a INT);
+CREATE TRIGGER tr1 BEFORE INSERT ON t1 FOR EACH ROW SET @@NEW.a=0;
+ERROR HY000: Unknown structured system variable or ROW routine variable 'NEW'
+DROP TABLE t1;
+#
+# MDEV-15615 Unexpected syntax error instead of "Unknown system variable" inside an SP
+#
+DECLARE
+a INT;
+BEGIN
+SET GLOBAL a=10;
+END;
+$$
+ERROR HY000: Unknown system variable 'a'
diff --git a/mysql-test/suite/compat/oracle/r/trigger.result b/mysql-test/suite/compat/oracle/r/trigger.result
index f77a56546fa..7c24c78bba6 100644
--- a/mysql-test/suite/compat/oracle/r/trigger.result
+++ b/mysql-test/suite/compat/oracle/r/trigger.result
@@ -1,10 +1,10 @@
 set sql_mode=ORACLE;
 :NEW.a := 1;
-ERROR 42000: You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'a := 1' at line 1
+ERROR 42000: You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near ':NEW.a := 1' at line 1
 :OLD.a := 1;
-ERROR 42000: You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'a := 1' at line 1
+ERROR 42000: You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near ':OLD.a := 1' at line 1
 :OLa.a := 1;
-ERROR 42000: You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'a := 1' at line 1
+ERROR 42000: You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near ':OLa.a := 1' at line 1
 SELECT :NEW.a;
 ERROR 42000: You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'a' at line 1
 SELECT :OLD.a;
diff --git a/mysql-test/suite/compat/oracle/t/parser.test b/mysql-test/suite/compat/oracle/t/parser.test
new file mode 100644
index 00000000000..5aa37c1cd33
--- /dev/null
+++ b/mysql-test/suite/compat/oracle/t/parser.test
@@ -0,0 +1,24 @@
+SET sql_mode=ORACLE;
+
+--echo #
+--echo # MDEV-15620 Crash when using "SET @@NEW.a=expr" inside a trigger
+--echo #
+
+CREATE TABLE t1 (a INT);
+--error ER_UNKNOWN_STRUCTURED_VARIABLE
+CREATE TRIGGER tr1 BEFORE INSERT ON t1 FOR EACH ROW SET @@NEW.a=0;
+DROP TABLE t1;
+
+--echo #
+--echo # MDEV-15615 Unexpected syntax error instead of "Unknown system variable" inside an SP
+--echo #
+
+DELIMITER $$;
+--error ER_UNKNOWN_SYSTEM_VARIABLE
+DECLARE
+  a INT;
+BEGIN
+  SET GLOBAL a=10;
+END;
+$$
+DELIMITER ;$$