Keep `isSuccess` consistent when refetching after an error

[markerikson]

This PR:

• Makes a further tweak to the logic for calculating isSuccess, such that we don't flip from false to true temporarily when refetching after an error

Fixes #4240

Investigation

Per #4240, if you have a sequence where:

• The initial fetch succeeds
• The first refetch fails
• You run a second refetch that also fails

the observed behavior is:

      [
        // Initial renders
        { id: 1, isFetching: true, isSuccess: false, isError: false },
        { id: 1, isFetching: true, isSuccess: false, isError: false },
        // Data is returned
        { id: 1, isFetching: false, isSuccess: true, isError: false },
        // Started first refetch
        { id: 1, isFetching: true, isSuccess: true, isError: false },
        // First refetch errored
        { id: 1, isFetching: false, isSuccess: false, isError: true },
        // Started second refetch <-------- `isSuccess` flips true here!
        { id: 1, isFetching: true, isSuccess: true, isError: false },
        // Second refetch errored
        { id: 1, isFetching: false, isSuccess: false, isError: true },
      ]

The issue is that isSuccess was false when the first refetch settled, but then flips to true when we start the second refetch. This does seem unintuitive and buggy.

Similar to #4731 , I think the logic for calculating isSuccess isn't sufficient. In this case:

• We know the current cache entry is not in a success state because it's fetching
• we are fetching and we do technically have cached data...
• but we know that the last request actually failed

Given that, I think the right thing to do is include && !lastResult?.isError, leaving us with:

    const isSuccess =
      currentState.isSuccess ||
      (hasData &&
        ((isFetching && !lastResult?.isError) || currentState.isUninitialized))

I see that flip the second refetch case to stay with isSuccess: false as I'd hope.

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1. entry point: @reduxjs/toolkit/query/react (cjs, production.min.cjs)	24.45 KB (-0.34% 🔽)
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3. createApi (react) (.modern.mjs)	15.66 KB (+0.06% 🔺)