placement: make Constraints can use dict format

[nolouch]

What problem does this PR solve?

Issue Number: close #47254

Problem Summary:
The customer wants to define a cluster with 5 replicas and distributed in 3 regions, leader can be in every region. currently, the rule in SQL cannot conver it.

//  cannot be 2:2:1 distributed
MySQL > create  placement policy mydeploy FOLLOWER_CONSTRAINTS='{ "+region=us-east-1":1, "+region=us-east-2": 2, "+region=us-west-1": 1}';

// leader is located in  us-east-1
MySQL > create  placement policy mydeploy  LEADER_CONSTRAINTS='{"+region=us-east-1":1}'  FOLLOWER_CONSTRAINTS='{ "+region=us-east-1":1, "+region=us-east-2": 2, "+region=us-west-1": 1}';


// cannot create
mysql> create placement policy mydeploy221 CONSTRAINTS='{ "+region=us-east-1":2, "+region=us-east-2": 2, "+region=us-west-1": 1}';
ERROR 1105 (HY000): invalid label constraints format: 'Constraints' should be [constraint1, ...] or any yaml compatible array representation

What is changed and how it works?

supports the dict format for CONSTRAINTS

create placement policy mydeploy221 CONSTRAINTS='{ "+region=us-east-1":2, "+region=us-east-2": 2, "+region=us-west-1": 1}'

Check List

Tests

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

Release note

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None

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Codecov Report

Merging #47344 (8448ec9) into master (9e4922a) will increase coverage by 0.6150%.
The diff coverage is 91.1764%.

Additional details and impacted files

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[nolouch]

/test unit-test

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[xhebox]

Maybe we can just use error from NewRulesWithDictConstraints, instead of Unmarshal before. Retuning ErrInvalidConstraintsFormat and wrap the error in NewRules.

[nolouch]

Here do precheck to ensure that it is in the actual dict format, then wrap two errors in NewRules or return dict constraints error(definitely it's dict format), it's easier to handle errors. otherwise, we need to unwrap errors from NewRulesWithDictConstraints and handle the error to remove the repeated string in the error message.

[nolouch]

/retest-required

[CabinfeverB]

rest LGTM
I found some info in docs https://docs.pingcap.com/tidb/stable/placement-rules-in-sql.

You can either specify constraints in list format ([+disk=ssd]) or in dictionary format ({+disk=ssd: 1,+disk=nvme: 2}).

It seems support dictionary format?

[CabinfeverB]

how about " specify follower count without specify follower constraints when specify other constraints"?
because we can specify follower count only.

[nolouch]

@CabinfeverB {+disk=ssd: 1,+disk=nvme: 2} supported in FOLLOW_CONSTRAINT and LEADER_CONSTRAINT, but not avaliable for CONSTRAINT

PTAL again

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: CabinfeverB, xhebox

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2023-10-08 02:36:15.45353053 +0000 UTC m=+933373.040640675: ☑️ agreed by xhebox.
• 2023-10-10 06:39:53.437293756 +0000 UTC m=+1120791.024403885: ☑️ agreed by CabinfeverB.