(graphcache) - Increase structural (deep) equality in normalized query results

[kitten]

Resolve #1860

Summary

This change enables Graphcache to compare new query results (from its normalized cache) with previous query results. While we previously had some remaining logic to reuse field values for mutations, we now extended the concept to queries as well. Graphcache will query each field and check whether it has changed, only creating new objects when a selection set has actually changed. This creates structural / deep referential equality in more parts of the query as it changes and potentially helps UI frameworks (e.g. React with useMemo and React.memo) to avoid more work.

In testing, I've noticed that currently (this isn't super optimized yet) this sacrifices about -10% of performance compared to the main branch. However, given that rendering may be much more expensive than querying our normalized cache we currently even deem this worth it. For typical queries we'd expect to see performance drop from an order of 20K operations per second to 18K, which means this won't be noticeable in typical use, but help development a lot.

I've checked the minzipped change of sizes ($ cat exchanges/graphcache/dist/*.min.mjs | gzip-size) and am seeing a change from 9.38kB to 9.61kB, a delta of 230B.

⚠️ Limitation: We're still focusing on UI update performance here, and not strict structural equality. This means that two different queries requesting the same entity with the same selection set will not be referentially equal.

Set of changes

• Store references to previously queried results in cacheExchange
• Pass previous references to query operations
• Refactor query operations (e.g. readSelection) to reuse references as much as possible

[changeset-bot]

🦋 Changeset detected

Latest commit: 10feac2

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	Minor

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[kitten]

We've released initial prerelease versions:

Package	Version
@urql/exchange-graphcache@deepeql	4.3.0-deepeql.0

This will automatically enable this PR's patch.