Non-terminating "test" actions

[LightAndLight]

I'd like to run a non-terminating --test-ghci command (a warp web server).

Currently this doesn't work as expected, because ghciwatch waits for the test action to finish before continuing to process events. I want events to be processed while the test action is running, so that the test action can be killed if a reload/restart event comes in.

[LightAndLight]

#143 (comment):

I'd really like to hear a proposed design, too, since I'm not sure how I'd implement that.

Abstractly, I want to:

1. Run the test action concurrently with the rest of the program
2. On the GHCi session thread, wait for the first of: {watcher event received, test action terminated}
3. Kill the test action if a watcher event is received before the test action has terminated

I could do this quite easily in Haskell. Much less sure of how to do it in Rust+Tokio. What follows is a sketch of how I'd start, but since I don't know much about the codebase or Tokio I mostly expect it to start the brainstorming.

The first thing I'd try is spawning the test call instead of awaiting it:

ghciwatch/src/ghci/mod.rs

Line 904 in cfd9de8

self.test(log).await?;

and returning a JoinHandle from finish_compilation and Ghci::initialize. The JoinHandle would be returned from Ghci::initialize in run_ghci:

ghciwatch/src/ghci/manager.rs

Lines 68 to 75 in cfd9de8

	tokio::select! {
	_ = handle.on_shutdown_requested() => {
	ghci.stop().await.wrap_err("Failed to quit ghci")?;
	}
	startup_result = ghci.initialize(&mut log, [LifecycleEvent::Startup(hooks::When::After)]) => {
	startup_result?;
	}
	}

and could then be waited on here:

ghciwatch/src/ghci/manager.rs

Lines 86 to 94 in cfd9de8

	let event = tokio::select! {
	_ = handle.on_shutdown_requested() => {
	ghci.lock().await.stop().await.wrap_err("Failed to quit ghci")?;
	break;
	}
	ret = receiver.recv() => {
	ret.ok_or_else(|| miette!("ghci event channel closed"))?
	}
	};

If an event happens before the test action task completes, the JoinHandle can be aborted.