Stop running cancel request in the main thread

[vinistock]

Motivation

This PR is another temporary solution for #3019. It reverts the other part of #2939.

Implementation

Essentially, we go back to pushing $/cancelRequest notifications to our incoming queue, rather than executing it straight away in the main thread.

This behaviour is incorrect because it essentially means no request will ever be cancelled. The order of operations is:

1. Get a request. Push it to the queue
2. Receive a cancellation notification for that request. Push it to the queue
3. Pop the request (messages are popped in order FIFO)
4. Fully process the request even though it was cancelled. Return a response
5. Now, we see the cancellation, which is of course too late. We already responded

There's no way this sequence of operations is correct, but for whatever reason reverting back to this fixes the LSP in NeoVim.

There are clearly things I'm not understanding about request cancellation and what editor/server are expected to do, so I will need to dig deeper to understand the underlying issue and how to properly implement it.

Note

The consequence of reverting back to the old behaviour is performance. Executing a request for which cancellation happened makes the server waste time generating a response that the editor is going to ignore anyway.

[vinistock]

• Stop running cancel request in the main thread #3028 👈 (View in Graphite)
• main

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