expression: move random_bytes from deferred to unfoldable functions

[kennytm]

What problem does this PR solve?

Issue Number: close #37412

Problem Summary: RANDOM_BYTES was marked as deferred by #16367. However, this is insufficient to prevent const-folding across rows.

What changed and how does it work?

Mark RANDOM_BYTES to unfoldable rather than deferred, in the same league as RAND and UUID.

(Thanks to suggestion from @‌unconsolable)

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No need to test

  • I checked and no code files have been changed.

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

When a query involving RANDOM_BYTES() returned multiple rows, the function is re-evaluated for every row in every invocation, ensuring randomness across the entire result set.

[sre-bot]

All committers have signed the CLA.

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[tiprow]

Hi @kennytm. Thanks for your PR.

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[kennytm]

/ok-to-test

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 72.8941%. Comparing base (74034d4) to head (443cb6e).

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #53795        +/-   ##
================================================
- Coverage   73.3645%   72.8941%   -0.4705%     
================================================
  Files          1624       1675        +51     
  Lines        448069     526378     +78309     
================================================
+ Hits         328724     383699     +54975     
- Misses        99207     120871     +21664     
- Partials      20138      21808      +1670     

Flag	Coverage Δ
integration	48.8924% <ø> (?)

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Components	Coverage Δ
dumpling	52.8766% <ø> (-0.0713%)	⬇️
parser	∅ <ø> (∅)
br	47.6277% <ø> (+2.1147%)	⬆️

[kennytm]

🤔 The failure is legit. The typeinfer_test requires that:

• RANDOM_BYTES(5) has type VARBINARY(1024) NOT NULL
• RANDOM_BYTES('123') has type VARBINARY(1024) NOT NULL
• RANDOM_BYTES('abc') has type VARBINARY(1024) NULL

Because this PR removed the const-folding, #23172 is not triggered and thus cannot mark RANDOM_BYTES(5) and RANDOM_BYTES('123') as NOT NULL (note that on MySQL the type is always BLOB NULL).

There are two paths to go next:

1. We declare that RANDOM_BYTES() always return VARBINARY(1024) NULL and change the test case
   • Because RANDOM_BYTES(NULL) is a thing, we cannot declare the function return type to be VARBINARY(1024) NOT NULL always.
2. We maintain the test case, which in turn requires creating a new category between "unfoldable" and "deferred" --- the type information is foldable but the value is not.

[hawkingrei]

/ok-to-test

[tiprow]

@kennytm: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
fast_test_tiprow	443cb6e	link	true	/test fast_test_tiprow

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[ti-chi-bot]

@kennytm: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
idc-jenkins-ci-tidb/build	443cb6e	link	true	/test build
idc-jenkins-ci-tidb/check_dev_2	443cb6e	link	true	/test check-dev2
idc-jenkins-ci-tidb/unit-test	443cb6e	link	true	/test unit-test

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