(graphcache) - Reenable cumulative optimistic updates

[kitten]

This was discovered in this Discussions thread: #1073

Summary

In #866 we previously disallowed optimistic updates to read other optimistically written data, which meant to prevent conflicts between these data layers that will later trickle down into permanent layers. This isn't a concern anymore because optimistic layers will never contribute to concrete, non-optimistic data and are thrown away, if they're for optimistic mutations.

The edge case we aimed to prevent is also not possible anymore because we now never apply concrete updates on top of optimistic ones since #750, namely:

• Block refetching of operations that have active optimistic updates and keep track of them (see above)
• Keep track of optimistic mutation that are pending at the same time, and flush their results simultaneously, also erasing the optimistically updated (i.e. blocked) dependencies at the same time

I'm not 100% sure anymore at this time, why we deemed this unsafe before, but it shouldn't be.

Set of changes

• Allow optimistic updates to see other optimistically written data
• Rename currentIgnoreOptimistic to just currentOptimistic
• Fix getNode to allow currentOptimistic to remain true so that updatePersist doesn't queue up noop updates for optimistic mutations

[changeset-bot]

🦋 Changeset detected

Latest commit: db86066

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@urql/exchange-graphcache	Patch

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[JoviDeCroock]

Great find!