expression: add builtin function JSON_DEPTH

[pingyu]

What problem does this PR solve?

Add json builtin function JSON_DEPTH described in #7546

What is changed and how it works?

Add struct builtinJSONDepthSig, and add GetElemDepth to BinaryJSON

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)

mysql> SELECT JSON_DEPTH('{}'), JSON_DEPTH('[]'), JSON_DEPTH('true');
+------------------+------------------+--------------------+
| JSON_DEPTH('{}') | JSON_DEPTH('[]') | JSON_DEPTH('true') |
+------------------+------------------+--------------------+
| 1 | 1 | 1 |
+------------------+------------------+--------------------+
1 row in set (0.00 sec)

mysql> SELECT JSON_DEPTH('[10, 20]'), JSON_DEPTH('[[], {}]');
+------------------------+------------------------+
| JSON_DEPTH('[10, 20]') | JSON_DEPTH('[[], {}]') |
+------------------------+------------------------+
| 2 | 2 |
+------------------------+------------------------+
1 row in set (0.00 sec)

mysql> SELECT JSON_DEPTH('[10, {"a": 20}]');
+-------------------------------+
| JSON_DEPTH('[10, {"a": 20}]') |
+-------------------------------+
| 3 |
+-------------------------------+
1 row in set (0.00 sec)

mysql> SELECT JSON_DEPTH(NULL);
+------------------+
| JSON_DEPTH(NULL) |
+------------------+
| NULL |
+------------------+
1 row in set (0.00 sec)

mysql> SELECT JSON_DEPTH('a');
ERROR 3140 (22032): Invalid JSON text: invalid character 'a' looking for beginning of value
mysql> SELECT JSON_DEPTH('{}') 'Result';
+--------+
| Result |
+--------+
| 1 |
+--------+
1 row in set (0.00 sec)

mysql> SELECT JSON_DEPTH('{"Name": "Homer"}') 'Result';
+--------+
| Result |
+--------+
| 2 |
+--------+
1 row in set (0.00 sec)

mysql> SET @DaTa = '{
'> "Person": {
'> "Name": "Homer",
'> "Age": 39,
'> "Hobbies": ["Eating", "Sleeping"]
'> }
'> }';
Query OK, 0 rows affected (0.00 sec)

mysql> SELECT JSON_DEPTH(@DaTa) 'Result';
+--------+
| Result |
+--------+
| 4 |
+--------+
1 row in set (0.00 sec)

Code changes

• Has exported function/method change
  Add GetElemDepth to BinaryJSON in types/json/binary_functions.go

Side effects

• NO

Related changes

• NO

---

This change is 

[sre-bot]

Hi contributor, thanks for your PR.

This patch needs to be approved by someone of admins. They should reply with "/ok-to-test" to accept this PR for running test automatically.

[CLAassistant]

All committers have signed the CLA.

[shenli]

/ok-to-test

[shenli]

@pingyu Thanks!

[shenli]

/run-all-tests

[shenli]

/run-integration-common-test

[pingyu]

@shenli With pleasure. I'm quite new to Go & contributing. Just tell me if I did something wrong. Thank you :)

[winoros]

lgtm
Please add tests in expression package too.

[shenli]

@XuHuaiyu PTAL
@pingyu Please address @winoros's comment.

[pingyu]

@winoros tests in expression package added. PTAL. Thanks.
Modified expression/builtin_json_test.go ONLY. Others codes rebased from latest master.

[pingyu]

@eurekaka PTAL. Thanks.
But I have no idea of how to manually test. And no new UT codes in distsql_builtin_test.go either. No similar codes existed made much difficulties to me. I'm still reading the distsql package.
Any suggestion ?

[eurekaka]

Currently, UT in distsql_builtin_test.go only covers Constant and Column expression, you can reference the TestEval to add the test for ScalarFunction.

[pingyu]

@eurekaka Got it. Thanks.

[zz-jason]

function json_depth() only accepts a single argument: https://github.com/pingcap/tidb/blob/master/expression/builtin.go#L596

how about:

bf := newBaseBuiltinFuncWithTp(ctx, args, types.ETInt, types.ETJson)

[pingyu]

OK.

[pingyu]

@eurekaka @zz-jason PTAL. Thanks.

[zz-jason]

LGTM

[eurekaka]

LGTM

[eurekaka]

/run-all-tests

[zz-jason]

/run-common-test

[zz-jason]

Reviewed 3 of 4 files at r1, 3 of 3 files at r3.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @eurekaka)

[eurekaka]

Reviewed 3 of 4 files at r1, 3 of 3 files at r3.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @eurekaka)