[VSCode] Allow to stop cargo on command

[jmg-duarte]

I've started developing some macros and recently I've hit a bug in my code which produced an infinite loop.
Once rust-analyzer starts running cargo the only way to stop it is to stop VSCode, this really hurts development, since VSCode now has the lock for the repo.
I should not need to stop the IDE to kill an external program from running, neither should I be expected to kill it with kill.
And even if I do kill it with kill, VSCode just restarts it...

A solution could be adding a button in the following dialog, which sends a SIGTERM signal to cargo?

[kjeremy]

I think the steps to solve this would be as follows:

1. Mark the flyweight progress tasks as cancellable and send that to the client. This would allow the client to present a UI suitable for cancellation
   https://github.com/rust-analyzer/rust-analyzer/blob/4d4f11925f793c45560c45c088d4b3139c2c171c/crates/rust-analyzer/src/lsp_utils.rs#L64-L76
2. Respond to cancel notifications from the client (fix Respond to WorkDoneProgressCancel notification #6782)
3. Murder the cargo check progress in cold blood.

We would probably need to store a map of progress tokens -> tasks somewhere.

[jmg-duarte]

@kjeremy thank you for the swift and comprehensive reply!
I'll try to look into it as I'd love to help.

[DJMcNab]

An alternative approach could be to add a concept of 'weak' processes to cargo itself. That is a 'weak' process, such as cargo check from within rust-analyzer would stop when cargo build is executed (using some method - creating a file?). That however is significantly more involved, and would be tangential to the suggested solution.