MDEV-12421 Check constraint with query crashes server and renders DB unusable

parse CHECK constraint *before* Column_definition validity checks

mysql-test/r/check_constraint.result

@@ -140,3 +140,7 @@ create table t1 (a int, b int, check(a>0));
 alter table t1 drop column a;
 ERROR 42S22: Unknown column 'a' in 'CHECK'
 drop table t1;
+create table t1 (a int check (@b in (select user from mysql.user)));
+ERROR HY000: Function or expression 'select ...' cannot be used in the CHECK clause of `a`
+create table t1 (a int check (a > @b));
+ERROR HY000: Function or expression '@b' cannot be used in the CHECK clause of `a`

mysql-test/t/check_constraint.test

@@ -86,3 +86,11 @@ create table t1 (a int, b int, check(a>0));
 --error ER_BAD_FIELD_ERROR
 alter table t1 drop column a;
 drop table t1;
+
+#
+# MDEV-12421 Check constraint with query crashes server and renders DB unusable
+#
+--error ER_GENERATED_COLUMN_FUNCTION_IS_NOT_ALLOWED
+create table t1 (a int check (@b in (select user from mysql.user)));
+--error ER_GENERATED_COLUMN_FUNCTION_IS_NOT_ALLOWED
+create table t1 (a int check (a > @b));

sql/sql_yacc.yy

@@ -6013,8 +6013,8 @@ field_list_item:
         ;
 
 column_def:
-          field_spec opt_check_constraint
-          { $$= $1;  $$->check_constraint= $2; }
+          field_spec
+          { $$= $1; }
         | field_spec references
           { $$= $1; }
         ;
@@ -6152,11 +6152,13 @@ field_spec:
             lex->init_last_field(f, $1.str, NULL);
             $<create_field>$= f;
           }
-          field_type_or_serial
+          field_type_or_serial opt_check_constraint
           {
             LEX *lex=Lex;
             $$= $<create_field>2;
 
+            $$->check_constraint= $4;
+
             if ($$->check(thd))
               MYSQL_YYABORT;