planner: add mutable and immutable ft implementation

[AilinKid]

What problem does this PR solve?

Issue Number: ref #51664

Problem Summary:

What changed and how does it work?

Introduce mutable interface{immutable interface{basic structure}} embedded level
From an inheritance perspective: it goes down like the below:

// currently the Mutable and Immutable and basic ft is organized as multi level interface wrapping.
// why use interface embedding is for no-loss downcast and upcast between mutable pointer and the
// immutable one.
//
//		    type ImmutableFieldType interface { // grandparent -----+            <------+
//			// GET methods & makeImmutable                      |                   |
//		     }                                                      | (downcast)        | (upcast)
//			                                                    |                   |
//		    type MutableFieldType interface {   // parent      <----+            <------+
//		        ImmutableFieldType                                  |                   |
//	                // SET methods & makeMutable                        |                   |
//		    }                                                       |                   |
//	                                                                    | (downcast)        | (upcast)
//		    type FieldType struct {             // son              |                   |
//		        ...                                                 |                   |
//		    }                                                  <----+            -------+

Holding a mutable pointer, you can get access to all SET methods, and implicit upcast as immutable allows it to get access to all GET methods (just like write lock is a superset of read lock, while with all functionality the latter has)[upcast is no loss, implicit]

Holding an immutable pointer, you can only get access to all GET methods. The only way you can change a thing is to make a mutableRef from the current immutable pointer, we do this with golang.(type) declaration inside, because the basic structure has implemented both of them. [downcast is no loss, explicit]. mutableCopy is another way to make a brand-new copy of itself with mutability.

what's the difference between the interface embedding and structure embedding, the former can use golang.(type) to do no-loss downcast and upcast, while the latter can hardly do that, even with structure pointer embedding, when you hold an internal structure pointer(say immutable here), if you want to convert it into a mutable one(son type), the only way you can do that is to create a new mutable structure again and wrap current parent pointer, actually it costs unsafe.size(8) comparatively to create a mutable structure with pointer-type element inside. It even costs more if additional elements are defined in your mutable structure.

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.

None

[tiprow]

Hi @AilinKid. Thanks for your PR.

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[codecov]

Codecov Report

Merging #51916 (782c7f3) into master (af76c2f) will decrease coverage by 15.8703%.
Report is 27 commits behind head on master.
The diff coverage is 75.0000%.

Additional details and impacted files

@@                Coverage Diff                @@
##             master     #51916         +/-   ##
=================================================
- Coverage   70.7202%   54.8500%   -15.8703%     
=================================================
  Files          1477       1590        +113     
  Lines        438443     612543     +174100     
=================================================
+ Hits         310068     335980      +25912     
- Misses       108950     253266     +144316     
- Partials      19425      23297       +3872     

Flag	Coverage Δ
integration	36.7674% <0.0000%> (?)
unit	70.6612% <75.0000%> (+0.1426%)	⬆️

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Components	Coverage Δ
dumpling	53.9957% <ø> (ø)
parser	∅ <ø> (∅)
br	51.2048% <ø> (+5.3300%)	⬆️

[AilinKid]

/test check-dev2

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[AilinKid]

/ok-to-test

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[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: hawkingrei
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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-03-20 12:06:53.088049502 +0000 UTC m=+1464840.110295890: ☑️ agreed by hawkingrei.

[hawkingrei]

/retest

[AilinKid]

After discussion with the team, the current TiDB implementation is bottlenecked with the mutable reference-related problem, like the current *ft pointer stored in multiple operators(kind of sharing), one changed, and the other is unaware of, thus causing some data and field type miss matching panic at runtime.

Even after this exploration, the multi-reference to the same mutable reference(or from x-casted) also existed, so nothing meaningful. We don't deal with too many language-related problems, here is related to mutable implementation in Golang, being safe is only guaranteed with ref-count. Otherwise, caution with coding is the responsibility that the owner should take.

If you want to explore a perfect solution to mutable ref(ban multi-mut ref), this pull request is not enough; otherwise, from the encapsulation prospect of mutable and immutable usage of the protected core structure, this PR is adequate. So it's a choice problem.