Fix observeFragment triggering unhandled rejections on network error

[XiNiHa]

This PR fixes an issue where observeFragment triggers unhandled rejections on network error, which happens because of the dangling promise created and dropped.

[captbaritone]

Thanks for the PR. Is it possible to construct a regression test?

[XiNiHa]

Thanks for the PR. Is it possible to construct a regression test?

You can now switch to 4e2c53a and see the test failing :)

btw, while working on the test, I realized that the current behavior is somewhat unnatural since it doesn't notify the observer at all when network errors occur. While I also think that it's inappropriate to return network errors from fragment observation, I believe it should fallback to returning missing data at least 🤔

[captbaritone]

Good catch that we don't model query errors as fragment errors. Given that's existing behavior, maybe we can tackle that as a second PR. Mind opening an issue?

[facebook-github-bot]

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[XiNiHa]

Good catch that we don't model query errors as fragment errors. Given that's existing behavior, maybe we can tackle that as a second PR. Mind opening an issue?

#4888 ✅