Refactor ObservableQuery#getCurrentResult to reenable immediate delivery of warm cache results.

[benjamn]

The crucial commit is the final one, which fixes #6659 and #6686 by making the getCurrentResult method of ObservableQuery return a result with loading: false when the cache provides complete data, assuming the FetchPolicy is cache-first or cache-only (the two policies that allow for non-loading results from the cache).

The general principle here is that getCurrentResult should return either the result most recently delivered to the ObservableQuery, or (if no result has been delivered yet) the next result that will be delivered. In cases where the cache is already primed with the necessary data (perhaps by a parent UI component), that next result can have loading: false, so it's important that getCurrentResult also returns a loading: false result in those cases.

Since queryInfo.networkStatus defaults to NetworkStatus.loading when QueryInfo objects are first initialized in QueryManager#watchQuery, getCurrentResult code was confused by queryInfo.networkStatus, and missed the opportunity to deliver non-loading results when the cache is warm.

I've never been happy with getCurrentResult and getCurrentQueryResult, so I also took this opportunity to unify those methods and simplify the surrounding logic.

[benjamn]

Always updating this.lastResult makes more sense now that ApolloQueryResult contains the partial boolean field. We last considered this logic in #6417.

[hwillson]

Fantastic @benjamn - everything looks great, and thanks very much for retiring ApolloCurrentQueryResult at the same time! 🙇‍♂️

[jimrandomh]

Thanks for this! I'll give this branch a try (and I expect several others will as well).

There's one more case, which a quick skim of the code suggests might not be handled correctly: when fetchPolicy is cache-and-network, but it isn't going to be fetched because of ssrForceFetchDelay or disableNetworkFetches (as described in #4814).

[trompx]

In which version is this supposed to be fixed? With version 3.1.5 and this:

const { user, loading } = useMe();
if (loading) {
  return <>Loading</>;
}

When I reload the pageI get the warning Warning: Text content did not match. Server: "Hello" Client: "Loading"
If I switch to:

const { user, loading } = useMe();
if (!user) {
  return <>Loading</>;
}

like mentionned here, that works

I also don't get the warning if I set apollo client fetchPolicy to no-cache.
Update : just tried version v3.2.0-rc.0 and still having this issue.

[arvindell]

@trompx I am experiencing the same behavior in AC3.3