MDEV-13313 JSON type alias is insufficiently compatible

make JSON an alias for LONGTEXT CHARACTER SET utf8mb4 COLLATE utf8mb4_bin

(same collation that item_jsonfunc.cc is using internally)

mysql-test/r/type_json.result

@@ -2,19 +2,21 @@ create or replace table t1(a json);
 show create table t1;
 Table	Create Table
 t1	CREATE TABLE `t1` (
-  `a` text DEFAULT NULL
+  `a` longtext CHARACTER SET utf8mb4 COLLATE utf8mb4_bin DEFAULT NULL
 ) ENGINE=MyISAM DEFAULT CHARSET=latin1
-create or replace table t1(a json character set utf8 default '{a:1}');
+create or replace table t1(a json character set utf8);
+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 'character set utf8)' at line 1
+create or replace table t1(a json default '{a:1}');
 show create table t1;
 Table	Create Table
 t1	CREATE TABLE `t1` (
-  `a` text CHARACTER SET utf8 DEFAULT '{a:1}'
+  `a` longtext CHARACTER SET utf8mb4 COLLATE utf8mb4_bin DEFAULT '{a:1}'
 ) ENGINE=MyISAM DEFAULT CHARSET=latin1
-create or replace table t1(a json binary not null check (json_valid(a)));
+create or replace table t1(a json not null check (json_valid(a)));
 show create table t1;
 Table	Create Table
 t1	CREATE TABLE `t1` (
-  `a` text CHARACTER SET latin1 COLLATE latin1_bin NOT NULL CHECK (json_valid(`a`))
+  `a` longtext CHARACTER SET utf8mb4 COLLATE utf8mb4_bin NOT NULL CHECK (json_valid(`a`))
 ) ENGINE=MyISAM DEFAULT CHARSET=latin1
 insert t1 values ('[]');
 insert t1 values ('a');
@@ -24,7 +26,7 @@ create or replace table t1(a json default(json_object('now', now())));
 show create table t1;
 Table	Create Table
 t1	CREATE TABLE `t1` (
-  `a` text DEFAULT json_object('now',current_timestamp())
+  `a` longtext CHARACTER SET utf8mb4 COLLATE utf8mb4_bin DEFAULT json_object('now',current_timestamp())
 ) ENGINE=MyISAM DEFAULT CHARSET=latin1
 insert t1 values ();
 select * from t1;

mysql-test/t/type_json.test

@@ -5,10 +5,13 @@
 create or replace table t1(a json);
 show create table t1;
 
-create or replace table t1(a json character set utf8 default '{a:1}');
+--error ER_PARSE_ERROR
+create or replace table t1(a json character set utf8);
+
+create or replace table t1(a json default '{a:1}');
 show create table t1;
 
-create or replace table t1(a json binary not null check (json_valid(a)));
+create or replace table t1(a json not null check (json_valid(a)));
 show create table t1;
 insert t1 values ('[]');
 --error ER_CONSTRAINT_FAILED

sql/sql_yacc.yy

@@ -6478,8 +6478,11 @@ field_type:
           { $$.set(MYSQL_TYPE_SET); }
         | LONG_SYM opt_binary
           { $$.set(MYSQL_TYPE_MEDIUM_BLOB); }
-        | JSON_SYM opt_binary
-          { $$.set(MYSQL_TYPE_BLOB); }
+        | JSON_SYM
+          {
+            Lex->charset= &my_charset_utf8mb4_bin;
+            $$.set(MYSQL_TYPE_LONG_BLOB);
+          }
         ;
 
 spatial_type: