Fix an issue where incorrect results are returned when changing variables and skipping

[jerelmiller]

Fixes #12458

If a query changed variables and simultaneously skipped a query, QueryInfo would get updated with the right variables, but the previous cache.watch was active. This was a problem when the fetchPolicy changed to standby as a result of skipping the query while changing variables. If something else cache a cache update during the period while the query was in standby, the diff was updated to the result from the previous variables which meant the next time queryInfo.getDiff() was called, it used the already stored wrong result.

This change cancels a cache.watch if variables change so that cache updates while a query is skipped don't update QueryInfo.

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Latest commit: fba44bf

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@apollo/client	Patch

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[github-actions]

size-limit report 📦

Path	Size
dist/apollo-client.min.cjs	41.27 KB (+0.05% 🔺)
import { ApolloClient, InMemoryCache, HttpLink } from "@apollo/client" (CJS)	50.72 KB (+0.04% 🔺)
import { ApolloClient, InMemoryCache, HttpLink } from "@apollo/client" (production) (CJS)	47.8 KB (+0.05% 🔺)
import { ApolloClient, InMemoryCache, HttpLink } from "@apollo/client"	36.27 KB (+0.06% 🔺)
import { ApolloClient, InMemoryCache, HttpLink } from "@apollo/client" (production)	33.66 KB (+0.06% 🔺)
import { ApolloProvider } from "@apollo/client/react"	1.26 KB (0%)
import { ApolloProvider } from "@apollo/client/react" (production)	1.24 KB (0%)
import { useQuery } from "@apollo/client/react"	5.21 KB (0%)
import { useQuery } from "@apollo/client/react" (production)	4.29 KB (0%)
import { useLazyQuery } from "@apollo/client/react"	4.78 KB (0%)
import { useMutation } from "@apollo/client/react"	3.62 KB (0%)
import { useMutation } from "@apollo/client/react" (production)	2.84 KB (0%)
import { useSubscription } from "@apollo/client/react"	4.42 KB (0%)
import { useSubscription } from "@apollo/client/react" (production)	3.48 KB (0%)
import { useSuspenseQuery } from "@apollo/client/react"	5.89 KB (0%)
import { useSuspenseQuery } from "@apollo/client/react" (production)	4.55 KB (0%)
import { useBackgroundQuery } from "@apollo/client/react"	5.38 KB (0%)
import { useBackgroundQuery } from "@apollo/client/react" (production)	4.04 KB (0%)
import { useLoadableQuery } from "@apollo/client/react"	5.47 KB (0%)
import { useLoadableQuery } from "@apollo/client/react" (production)	4.12 KB (0%)
import { useReadQuery } from "@apollo/client/react"	3.43 KB (0%)
import { useReadQuery } from "@apollo/client/react" (production)	3.37 KB (0%)
import { useFragment } from "@apollo/client/react"	2.36 KB (0%)
import { useFragment } from "@apollo/client/react" (production)	2.31 KB (0%)

[jerelmiller]

This is one of the core issues at heart. When variables change and skipping a query (which sets the fetchPolicy to standby), getDiff is not called, which meant that updateWatch in QueryInfo was not called with the new variables. If a cache update occurred while the query was in standby (line 1697 in this test), the lastDiff was updated with the result from old variables. QueryInfo.getDiff() then just returned that lastDiff from that point forward because it didn't think variables had changed.

[jerelmiller]

I was able to whittle this reproduction down to skip and variables without the need for another query to reproduce. The trick is writing to change variables and set skip at the same time, then issue cache updates while the query is in standby to reproduce this behavior.

[phryneas]

Phew, that one looks like it was tricky to find - good call!