Preserve ModifyIndex for unchanged entry in KVS TXN

[a-zagaevskiy]

These changes are made to preserve ModifyIndex for entries that are left untouched in the KVStore during a transaction.

[freddygv]

Hi @a-zagaevskiy, can you please add a test to /agent/consul/state/txn_test.go?

It would be based on this following test, but would run multiple KVSet operations instead of running every possible operation once:

consul/agent/consul/state/txn_test.go

Line 510 in 57096f8

func TestStateStore_Txn_KVS(t *testing.T) {

[a-zagaevskiy]

Hi @freddygv ! Is it okay?

To be honest, I'm not sure that I chose an appropriate name for the test. And there are some doubts about how I've set up that commits. But I would be glad for your help.

[freddygv]

This looks good, I made one other minor comment.

[freddygv]

Thanks for the issue and fix in a PR @a-zagaevskiy. This is good to merge now!

[a-zagaevskiy]

Glad I could help a little!

And what about the corresponding issue? Should I close it manually right now? It looks like I didn't link it properly with this PR.

[freddygv]

Ah yep. In order to auto-close issues the PR description needs contain:
Fixes #7826

I just closed the issue though. Thanks for the reminder.