Fix weight calculation of decideRebalance when explain

[HUSTERGS]

Description

The explain api POST _cluster/allocation/explain, explains how an allocation decision is made, but during the calculation of currentWeight in

OpenSearch/server/src/main/java/org/opensearch/cluster/routing/allocation/allocator/LocalShardsBalancer.java

Line 209 in 399188f

MoveDecision decideRebalance(final ShardRouting shard) {

, it uses original weight function which does not consider allocation/rebalance constraint:

OpenSearch/server/src/main/java/org/opensearch/cluster/routing/allocation/allocator/LocalShardsBalancer.java

Lines 234 to 238 in 399188f

	// balance the shard, if a better node can be found
	final String idxName = shard.getIndexName();
	final float currentWeight = weight.weight(this, currentNode, idxName);
	final AllocationDeciders deciders = allocation.deciders();
	Decision.Type rebalanceDecisionType = Decision.Type.NO;

However the following calculation uses the new weightWithRebalanceConstraints, which is correct

OpenSearch/server/src/main/java/org/opensearch/cluster/routing/allocation/allocator/LocalShardsBalancer.java

Lines 250 to 254 in 399188f

	// that should be on each node on average (both taking the cluster as a whole into account
	// as well as shards per index)
	final float nodeWeight = weight.weightWithRebalanceConstraints(this, node, idxName);
	// if the node we are examining has a worse (higher) weight than the node the shard is
	// assigned to, then there is no way moving the shard to the node with the worse weight

So change the former calculation of currentNode weight to use the new weightWithRebalanceConstraints function

Related Issues

Resolves #[Issue number to be closed when this PR is merged]

Check List

• Functionality includes testing.
• API changes companion pull request created, if applicable.
• Public documentation issue/PR created, if applicable.

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[github-actions]

❌ Gradle check result for 01331d5: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[alchemist51]

The changes looks good to me!

[github-actions]

❌ Gradle check result for 01331d5: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[github-actions]

❕ Gradle check result for 01331d5: UNSTABLE

Please review all flaky tests that succeeded after retry and create an issue if one does not already exist to track the flaky failure.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 72.53%. Comparing base (399188f) to head (01331d5).
Report is 17 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main   #17720      +/-   ##
============================================
+ Coverage     72.46%   72.53%   +0.06%     
- Complexity    65855    65921      +66     
============================================
  Files          5322     5322              
  Lines        305477   305477              
  Branches      44312    44312              
============================================
+ Hits         221359   221572     +213     
+ Misses        66023    65729     -294     
- Partials      18095    18176      +81     

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