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.

11 files changed, 125 insertions, 45 deletions

diff --git a/sql/CMakeLists.txt b/sql/CMakeLists.txt
index 0befcd25204..18b7cc3176d 100644
--- a/sql/CMakeLists.txt
+++ b/sql/CMakeLists.txt
@@ -132,7 +132,7 @@ SET (SQL_SOURCE
                rpl_gtid.cc rpl_parallel.cc
                semisync.cc semisync_master.cc semisync_slave.cc
                semisync_master_ack_receiver.cc
-               sql_type.cc
+               sql_type.cc sql_type_json.cc
                item_windowfunc.cc sql_window.cc
 	       sql_cte.cc
                item_vers.cc
diff --git a/sql/field.cc b/sql/field.cc
index 89b04c4d795..5289798cebf 100644
--- a/sql/field.cc
+++ b/sql/field.cc
@@ -10501,6 +10501,13 @@ bool Column_definition::fix_attributes_temporal_with_time(uint int_part_length)
 }
 
 
+bool Column_definition::validate_check_constraint(THD *thd)
+{
+  return check_constraint &&
+         check_expression(check_constraint, &field_name, VCOL_CHECK_FIELD);
+}
+
+
 bool Column_definition::check(THD *thd)
 {
   DBUG_ENTER("Column_definition::check");
@@ -10515,9 +10522,8 @@ bool Column_definition::check(THD *thd)
       DBUG_RETURN(TRUE);
   }
 
-  if (check_constraint &&
-      check_expression(check_constraint, &field_name, VCOL_CHECK_FIELD))
-      DBUG_RETURN(1);
+  if (type_handler()->Column_definition_validate_check_constraint(thd, this))
+    DBUG_RETURN(TRUE);
 
   if (default_value)
   {
diff --git a/sql/field.h b/sql/field.h
index 25d9f0e0ca4..30098afe953 100644
--- a/sql/field.h
+++ b/sql/field.h
@@ -4675,6 +4675,7 @@ public:
   bool fix_attributes_bit();
 
   bool check(THD *thd);
+  bool validate_check_constraint(THD *thd);
 
   bool stored_in_db() const { return !vcol_info || vcol_info->stored_in_db; }
 
diff --git a/sql/sql_lex.cc b/sql/sql_lex.cc
index f5e37446b58..df4d8d7b94c 100644
--- a/sql/sql_lex.cc
+++ b/sql/sql_lex.cc
@@ -9587,21 +9587,3 @@ bool LEX::sp_proc_stmt_statement_finalize(THD *thd, bool no_lookahead)
                                                        lip->get_tok_start());
   return LEX::sp_proc_stmt_statement_finalize_buf(thd, qbuf);
 }
-
-
-/**
-   Create JSON_VALID(field_name) expression
-*/
-
-Virtual_column_info *make_json_valid_expr(THD *thd, LEX_CSTRING *field_name)
-{
-  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);
-}
diff --git a/sql/sql_lex.h b/sql/sql_lex.h
index fc451b21816..3f3fef8a414 100644
--- a/sql/sql_lex.h
+++ b/sql/sql_lex.h
@@ -148,7 +148,7 @@ public:
   bool copy_or_convert(THD *thd, const Lex_ident_cli_st *str, CHARSET_INFO *cs);
   bool is_null() const { return str == NULL; }
   bool to_size_number(ulonglong *to) const;
-  void set_valid_utf8(LEX_CSTRING *name)
+  void set_valid_utf8(const LEX_CSTRING *name)
   {
     DBUG_ASSERT(Well_formed_prefix(system_charset_info, name->str,
                                    name->length).length() == name->length);
@@ -4640,6 +4640,5 @@ Item* handle_sql2003_note184_exception(THD *thd, Item* left, bool equal,
 void sp_create_assignment_lex(THD *thd, bool no_lookahead);
 bool sp_create_assignment_instr(THD *thd, bool no_lookahead);
 
-Virtual_column_info *make_json_valid_expr(THD *thd, LEX_CSTRING *field_name);
 #endif /* MYSQL_SERVER */
 #endif /* SQL_LEX_INCLUDED */
diff --git a/sql/sql_type.cc b/sql/sql_type.cc
index 1812294ed46..4906eee064d 100644
--- a/sql/sql_type.cc
+++ b/sql/sql_type.cc
@@ -66,7 +66,6 @@ Type_handler_tiny_blob   type_handler_tiny_blob;
 Type_handler_medium_blob type_handler_medium_blob;
 Type_handler_long_blob   type_handler_long_blob;
 Type_handler_blob        type_handler_blob;
-Type_handler_json        type_handler_json;
 static Type_handler_blob_compressed type_handler_blob_compressed;
 
 Type_handler_interval_DDhhmmssff type_handler_interval_DDhhmmssff;
@@ -2328,6 +2327,17 @@ Field *Type_handler_set::make_conversion_table_field(TABLE *table,
                    ((const Field_enum*) target)->typelib, target->charset());
 }
 
+
+/*************************************************************************/
+
+bool Type_handler::
+       Column_definition_validate_check_constraint(THD *thd,
+                                                   Column_definition * c) const
+{
+  return c->validate_check_constraint(thd);
+}
+
+
 /*************************************************************************/
 bool Type_handler_null::
        Column_definition_fix_attributes(Column_definition *def) const
diff --git a/sql/sql_type.h b/sql/sql_type.h
index 7216b24835d..23a3f7fccb7 100644
--- a/sql/sql_type.h
+++ b/sql/sql_type.h
@@ -78,6 +78,7 @@ struct Schema_specification_st;
 struct TABLE;
 struct SORT_FIELD_ATTR;
 class Vers_history_point;
+class Virtual_column_info;
 
 #define my_charset_numeric      my_charset_latin1
 
@@ -3280,7 +3281,6 @@ public:
     return true;
   }
   virtual bool is_scalar_type() const { return true; }
-  virtual bool is_json_type() const { return false; }
   virtual bool can_return_int() const { return true; }
   virtual bool can_return_decimal() const { return true; }
   virtual bool can_return_real() const { return true; }
@@ -3338,6 +3338,10 @@ public:
   // Automatic upgrade, e.g. for ALTER TABLE t1 FORCE
   virtual void Column_definition_implicit_upgrade(Column_definition *c) const
   { }
+  // Validate CHECK constraint after the parser
+  virtual bool Column_definition_validate_check_constraint(THD *thd,
+                                                           Column_definition *c)
+                                                           const;
   // Fix attributes after the parser
   virtual bool Column_definition_fix_attributes(Column_definition *c) const= 0;
   /*
@@ -5895,14 +5899,6 @@ public:
 };
 
 
-class Type_handler_json: public Type_handler_long_blob
-{
-public:
-  virtual ~Type_handler_json() {}
-  virtual bool is_json_type() const { return true; }
-};
-
-
 class Type_handler_blob: public Type_handler_blob_common
 {
   static const Name m_name_blob;
@@ -6231,7 +6227,6 @@ extern MYSQL_PLUGIN_IMPORT Type_handler_hex_hybrid  type_handler_hex_hybrid;
 extern MYSQL_PLUGIN_IMPORT Type_handler_tiny_blob   type_handler_tiny_blob;
 extern MYSQL_PLUGIN_IMPORT Type_handler_medium_blob type_handler_medium_blob;
 extern MYSQL_PLUGIN_IMPORT Type_handler_long_blob   type_handler_long_blob;
-extern MYSQL_PLUGIN_IMPORT Type_handler_json        type_handler_json;
 extern MYSQL_PLUGIN_IMPORT Type_handler_blob        type_handler_blob;
 
 extern MYSQL_PLUGIN_IMPORT Type_handler_bool        type_handler_bool;
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);
+}
diff --git a/sql/sql_type_json.h b/sql/sql_type_json.h
new file mode 100644
index 00000000000..6c4ee8cb2eb
--- /dev/null
+++ b/sql/sql_type_json.h
@@ -0,0 +1,38 @@
+#ifndef SQL_TYPE_JSON_INCLUDED
+#define SQL_TYPE_JSON_INCLUDED
+/*
+   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 "mariadb.h"
+#include "sql_type.h"
+
+class Type_handler_json_longtext: public Type_handler_long_blob
+{
+  Virtual_column_info *make_json_valid_expr(THD *thd,
+                                            const LEX_CSTRING *field_name)
+                                            const;
+public:
+  virtual ~Type_handler_json_longtext() {}
+  bool Column_definition_validate_check_constraint(THD *thd,
+                                                   Column_definition *c) const;
+};
+
+extern MYSQL_PLUGIN_IMPORT
+  Type_handler_json_longtext type_handler_json_longtext;
+
+#endif // SQL_TYPE_JSON_INCLUDED
diff --git a/sql/sql_yacc.yy b/sql/sql_yacc.yy
index 0a2961b8154..00566c463e8 100644
--- a/sql/sql_yacc.yy
+++ b/sql/sql_yacc.yy
@@ -68,6 +68,7 @@
 #include "sql_lex.h"
 #include "sql_sequence.h"
 #include "my_base.h"
+#include "sql_type_json.h"
 
 /* this is to get the bison compilation windows warnings out */
 #ifdef _MSC_VER
@@ -6689,10 +6690,6 @@ field_spec:
             $$= $<create_field>2;
 
             $$->check_constraint= $4;
-            if (!$4 && lex->last_field->type_handler()->is_json_type() &&
-                !($$->check_constraint= make_json_valid_expr(thd,
-                                                             &$$->field_name)))
-              MYSQL_YYABORT;
 
             if (unlikely($$->check(thd)))
               MYSQL_YYABORT;
@@ -7086,7 +7083,7 @@ field_type_lob:
         | JSON_SYM
           {
             Lex->charset= &my_charset_utf8mb4_bin;
-            $$.set(&type_handler_json);
+            $$.set(&type_handler_json_longtext);
           }
         ;
 
diff --git a/sql/sql_yacc_ora.yy b/sql/sql_yacc_ora.yy
index 3bfb8347b13..025241f8e93 100644
--- a/sql/sql_yacc_ora.yy
+++ b/sql/sql_yacc_ora.yy
@@ -68,6 +68,7 @@
 #include "sql_lex.h"
 #include "sql_sequence.h"
 #include "my_base.h"
+#include "sql_type_json.h"
 
 /* this is to get the bison compilation windows warnings out */
 #ifdef _MSC_VER
@@ -6627,10 +6628,6 @@ field_spec:
             $$= $<create_field>2;
 
             $$->check_constraint= $4;
-            if (!$4 && lex->last_field->type_handler()->is_json_type() &&
-                !($$->check_constraint= make_json_valid_expr(thd,
-                                                             &$$->field_name)))
-              MYSQL_YYABORT;
 
             if (unlikely($$->check(thd)))
               MYSQL_YYABORT;
@@ -7076,7 +7073,7 @@ field_type_lob:
         | JSON_SYM
           {
             Lex->charset= &my_charset_utf8mb4_bin;
-            $$.set(&type_handler_json);
+            $$.set(&type_handler_json_longtext);
           }
         ;