JSON "Unsupported functions" already in server

[kolbe]

The documentation for a long time has included several items in the "Unsupported functions" section of the "JSON Functions" documentation.

File: /release-6.1/functions-and-operators/json-functions.md

But these functions have actually been in the server for quite a while... since 5.1.0 or 5.2.0!

5.7.25-TiDB-v5.1.0 (root) [test]> select tidb_version()\G
*************************** 1. row ***************************
tidb_version(): Release Version: v5.1.0
Edition: Community
Git Commit Hash: 8acd5c88471cb7b4d4c4a8ed73b4d53d6833f13e
Git Branch: heads/refs/tags/v5.1.0
UTC Build Time: 2021-06-24 07:08:50
GoVersion: go1.16.4
Race Enabled: false
TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306
Check Table Before Drop: false
1 row in set (0.001 sec)

5.7.25-TiDB-v5.1.0 (root) [test]> select json_pretty('{"doc":"JSON_PRETTY"}')\G
*************************** 1. row ***************************
json_pretty('{"doc":"JSON_PRETTY"}'): {
  "doc": "JSON_PRETTY"
}
1 row in set (0.001 sec)

5.7.25-TiDB-v5.2.0 (root) [test]> select tidb_version()\G
*************************** 1. row ***************************
tidb_version(): Release Version: v5.2.0
Edition: Community
Git Commit Hash: 05d2210647d6a1503a8d772477e43b14a024f609
Git Branch: heads/refs/tags/v5.2.0
UTC Build Time: 2021-08-27 05:54:47
GoVersion: go1.16.5
Race Enabled: false
TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306
Check Table Before Drop: false
1 row in set (0.001 sec)

5.7.25-TiDB-v5.2.0 (root) [test]> select json_merge_patch('{"a":0}','{"a":1}');
+---------------------------------------+
| json_merge_patch('{"a":0}','{"a":1}') |
+---------------------------------------+
| {"a": 1}                              |
+---------------------------------------+
1 row in set (0.001 sec)

5.7.25-TiDB-v5.2.0 (root) [test]> select json_arrayagg(c) from (select 1 as c union select 2 union select 3);
+------------------+
| json_arrayagg(c) |
+------------------+
| [3, 2, 1]        |
+------------------+
1 row in set (0.001 sec)

[TomShawn]

@lcwangchao Could you please update this document? Thanks~

[dveeden]

I think #8762 fixed this for the master branch
@kolbe could you check https://docs.pingcap.com/tidb/dev/json-functions ?

If things in the master branch are fine then the next thing we need is to backport this to the right release branches.

[kolbe]

Yes, you're very right that the master branch does include this content, I'm sorry I didn't mention that in my original report. Note that not all the functions were added to the server at the same time, so the backport/cherry-pick will need to be done carefully so that historical documentation versions are accurate.

[TomShawn]

@dveeden Can we cherry-pick #8762 to v5.4, v5.3, v5.2, and v5.1, and make sure every cherry-pick is accurate to that version?