expression: fix Invalid JSONs

[b41sh]

What problem does this PR solve?

fix Invalid JSONs #10468

What is changed and how it works?

check json is valid before UnmarshalJSON

Check List

Tests

• Unit test
• Integration test

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@7bf3d69). Click here to learn what that means.
The diff coverage is 80%.

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  Hits              ?      70105           
  Misses            ?      12805           
  Partials          ?       5193

[bb7133]

Thanks for contributing!

[bb7133]

LGTM

[XuHuaiyu]

Is it possible to make the error message be more similar to MySQL?

[b41sh]

Is it possible to make the error message be more similar to MySQL?

ok, Let me try

[zz-jason]

LGTM

[zz-jason]

/run-all-tests

[bb7133]

Hi @b41sh Unfortunately a corner case is triggered in some TiDB internal tests:

MySQL 5.7:

mysql> select CAST(CAST('1234abcd' AS BINARY) AS JSON);
+------------------------------------------+
| CAST(CAST('1234abcd' AS BINARY) AS JSON) |
+------------------------------------------+
| "base64:type253:MTIzNGFiY2Q="            |
+------------------------------------------+
1 row in set (0.01 sec)

TiDB in this PR:

tidb> select CAST(CAST('1234abcd' AS BINARY) AS JSON);
ERROR 3140 (22032): Invalid JSON text: The document root must not be followed by other values.

TiDB before this PR:

tidb> select CAST(CAST('1234abcd' AS BINARY) AS JSON);
+------------------------------------------+
| CAST(CAST('1234abcd' AS BINARY) AS JSON) |
+------------------------------------------+
| 1234                                     |
+------------------------------------------+
1 row in set (0.00 sec)

As is shown, there is another compatibility issue about JSON(possibly related to #9996) in TiDB. But it was hidden in previous tests because although the result was WRONG, no error was raised.

I think we may: comment related test cases to make this PR merged firstly, or wait until the binary(or say, base64) related issue is solved.

PTAL @zz-jason @XuHuaiyu

[bb7133]

I marked 'DNM' temporarily before we make the decision.

[bb7133]

/run-all-tests

[bb7133]

Thanks for contributing! @b41sh