A cleanup for MDEV-13916 Enforce check constraint on JSON type

1. Renaming Type_handler_json to Type_handler_json_longtext
   There will be other JSON handlers soon, e.g. Type_handler_json_varchar.

2. Making the code more symmetric for data types:

- Adding a new virtual method
  Type_handler::Column_definition_validate_check_constraint()
- Moving JSON-specific code from sql_yacc.yy to
  Type_handler_json_longtext::Column_definition_validate_check_constraint()

3. Adding new files sql_type_json.cc and sql_type_json.h
   and moving Type_handler+JSON related code into these files.

1 files changed, 55 insertions, 0 deletions

diff --git a/sql/sql_type_json.cc b/sql/sql_type_json.cc
new file mode 100644
index 00000000000..f53a247d816
--- /dev/null
+++ b/sql/sql_type_json.cc
@@ -0,0 +1,55 @@
+/*
+   Copyright (c) 2019, MariaDB
+
+   This program is free software; you can redistribute it and/or
+   modify it under the terms of the GNU General Public License
+   as published by the Free Software Foundation; version 2 of
+   the License.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA
+*/
+
+#include "sql_type_json.h"
+#include "sql_class.h"
+
+
+Type_handler_json_longtext  type_handler_json_longtext;
+
+
+/**
+   Create JSON_VALID(field_name) expression
+*/
+
+Virtual_column_info *
+Type_handler_json_longtext::make_json_valid_expr(THD *thd,
+                                                 const LEX_CSTRING *field_name)
+                                                 const
+{
+  Lex_ident_sys_st str;
+  Item *field, *expr;
+  str.set_valid_utf8(field_name);
+  if (unlikely(!(field= thd->lex->create_item_ident_field(thd, NullS, NullS,
+                                                          &str))))
+    return 0;
+  if (unlikely(!(expr= new (thd->mem_root) Item_func_json_valid(thd, field))))
+    return 0;
+  return add_virtual_expression(thd, expr);
+}
+
+
+bool Type_handler_json_longtext::
+       Column_definition_validate_check_constraint(THD *thd,
+                                                   Column_definition * c) const
+{
+  if (!c->check_constraint &&
+      !(c->check_constraint= make_json_valid_expr(thd, &c->field_name)))
+    return true;
+  return Type_handler::Column_definition_validate_check_constraint(thd, c);
+}