AC3: Memory leak in `watchQuery` retains `context` object in memory even after `unsubscribe`

Intended outcome:

Object passed as context to watchQuery method should be released when unsubscribe is called, instead of being retrained in memory.

I’m opening this because this seems like another symptom of a related issue, but with a testable reproduction, and including the heap snapshots files.

I believe this is very related to what @Torsten85 posted here: https://github.com/apollographql/apollo-client/issues/6985#issuecomment-701240849

Actual outcome: context object are retained in memory by AC3:

How to reproduce the issue: Use watchQuery with context set. Apollo keeps reference to that object even if query has done, and unsubscribe has been called (and all references has been destructed).

You can find a complete reproduction (as a Jest test + instructions) here: https://github.com/dotansimha/apollo-very-pessimism

Versions >=3

[benjamn]

Thanks to @dotansimha’s reproduction and @kamilkisiela’s proposed solution, I’m confident this leak is fixed in @apollo/client@3.2.4 and @apollo/client@3.3.0-beta.12. Thanks a ton!

[benjamn]

@dotansimha As a side note, the weak reference approach you used in your reproduction (using weak-napi) is 🤯 —definitely using that the next time I need to write a memory leak regression test that runs in Node!