expression, planner: make the Value field of the Constant struct private | tidb-test=pr/2355

[YangKeao]

What problem does this PR solve?

Issue Number: close #53504

Problem Summary:

Using .Value directly can easily cause wrong result and dangerous bug, especially for plan cache. We have found #53504 #53505 (and potentially many others). It's not possible to depend on test cases to avoid making mistakes in the future. Therefore, I propose to make .Value private.

What changed and how does it work?

However, it's not simple to make .Value private, because:

1. The Constant is always constructed directly, like Constant{Value:..., ...}. If we avoid using .Value directly, all these codes need to be changed.
2. The expression pkg is too big, and we also need to ensure the codes in expression pkg cannot access the .Value. However, golang allows the codes in the same package to access the private field.

Therefore, I wrote a linter to filter out all selector expression to get the .Value.

It's also hard to keep the correctness. I've considered the following three situations:

1. I just want to get the .Value field, and I'm sure it's not a parameter and deferred function.
2. I want to get the .Value field. If the current context is not in plan cache, evaluating parameter and deferred function is also fine.
3. I want to evaluate the parameter, deferred function, or simply return the value.

For most of the codes in optimizing stage, it should call 2. For the code in executing stage, it usually should call 3. We provide GetValue(), GetValueWithoutOverOptimization(), and .Eval for these three circumstances.

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.

Release note

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

Fix the issue that in some situation, the result is different if the query is using plan cache.

[ti-chi-bot]

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[codecov]

Codecov Report

Attention: Patch coverage is 23.16716% with 262 lines in your changes missing coverage. Please review.

Project coverage is 50.8441%. Comparing base (1469fcf) to head (8a1cd57).
Report is 936 commits behind head on master.

Additional details and impacted files

@@                Coverage Diff                @@
##             master     #54244         +/-   ##
=================================================
- Coverage   74.7940%   50.8441%   -23.9499%     
=================================================
  Files          1523       1643        +120     
  Lines        361510     608416     +246906     
=================================================
+ Hits         270388     309344      +38956     
- Misses        71504     275391     +203887     
- Partials      19618      23681       +4063     

Flag	Coverage Δ
integration	23.0266% <23.1671%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
dumpling	55.1994% <ø> (ø)
parser	∅ <ø> (∅)
br	48.6053% <ø> (+0.6375%)	⬆️

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@YangKeao: 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	8a1cd57	link	true	/test fast_test_tiprow

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[ti-chi-bot]

@YangKeao: 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
pull-mysql-client-test	8a1cd57	link	true	/test pull-mysql-client-test
idc-jenkins-ci-tidb/mysql-test	8a1cd57	link	true	/test mysql-test
idc-jenkins-ci-tidb/check_dev	8a1cd57	link	true	/test check-dev
idc-jenkins-ci-tidb/unit-test	8a1cd57	link	true	/test unit-test
idc-jenkins-ci-tidb/check_dev_2	8a1cd57	link	true	/test check-dev2

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[ti-chi-bot]

PR needs rebase.

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