Implement support for server initiated $/progress

[ebkalderon]

Background

This task was split from #176.

According to the relevant section in the specification, server initiated progress is defined as follows:

1. The server sends a window/workDoneProgress/create request (with a server-generated WorkDoneToken) to the client.
2. If it succeeds, the server sends $/progress begin/report/end notifications to the client using the same WorkDoneToken.
3. If it fails, the server must not send progress notifications using that WorkDoneToken at all.
4. The client may send a window/workDoneProgress/cancel notification to the server, requesting the $/progress notification stream with the given WorkDoneToken be canceled.

Implementation

To support this type of $/progress, we should do the following:

• [ ] Complete #380 first.
• [ ] Add a Client::server_progress() method which performs the following steps:
  1. Generates a new unique WorkDoneToken (either an incrementing integer ID or GUID would work).
  2. Sends a window/workDoneProgress/create request to the client with this WorkDoneToken attached.
  3. If it succeeds, the method simply delegates to Client::progress() with the server-generated WorkDoneToken.
  4. If it fails, it short-circuits with an Err(_) and no $/progress stream may be initiated for that token ever again.
• [ ] Add a LanguageServer::work_done_progress_cancel() trait method (corresponding to window/workDoneProgress/cancel), from which the server may cancel ongoing progress.
  • Cancellation is as simple as not doing anything with the OngoingProgress again. Simply dropping it should be sufficient.

[ematipico]

Any chance we could help here?