[DUX-1499] Support running an application

[9999years]

It's nice to run an application like a web server instead of running tests. This may require some additional hooks.

_{From SyncLinear.com | DUX-1499}

[running-grass]

@9999years

Thank you for implementing this feature. Now that the issue has been marked as completed, could you provide some guidance on how to use ghciwatch to run a server application? Specifically:

1. Are there any new configuration options or commands to enable server mode?
2. Is there documentation available on how to set up ghciwatch for running and auto-reloading a web server or similar application?
3. Are there any best practices or examples you can share for using this new functionality?

Any information on how to effectively utilize this new feature would be greatly appreciated by the community.

[9999years]

Filed a documentation ticket at #315, see #315 (comment) for an initial response (though there's still work to be done for this feature).

[LightAndLight]

This doesn't seem to work (tested on cfd9de8)

When --test-ghci is given a non-terminating IO action, the action isn't killed in response to reload/restart events. If I do something that would cause a reload/restart, then kill ghciwatch (e.g. with Ctrl+C), I see that the event was pending the termination of the --test-ghci action.

Example:

$ ghciwatch --command "cabal repl hedge-example" --watch hedge.cabal --restart-glob 'hedge.cabal' --watch src --restart-glob 'src/**/*.hs' --watch example --reload-glob 'example/Main.hs' --test-ghci main
Build profile: -w ghc-9.6.6 -O1
In order, the following will be built (use -v for more details):
 - hedge-0.1.0.0 (interactive) (exe:hedge-example) (first run)
Preprocessing executable 'hedge-example' for hedge-0.1.0.0...
GHCi, version 9.6.6: https://www.haskell.org/ghc/  :? for help

[1 of 2] Compiling Main             ( example/Main.hs, interpreted )
Ok, one module loaded.
• All good! Finished starting up in 738.02ms
• Running test command command=main
Server running on port 3000
^C
• Reloading ghci:
  • example/Main.hs

Error:   × Tasks failed:
  │ • run_ghci: channel closed

If I change main to something that terminates, then the above command works and correctly responds to changes.

[LightAndLight]

Right, GhciStdin::run_command is synchronous:

ghciwatch/src/ghci/mod.rs

Lines 921 to 923 in cfd9de8

	self.stdin
	.run_command(&mut self.stdout, command, log)
	.await?;

which calls

ghciwatch/src/ghci/stdin.rs

Lines 28 to 46 in cfd9de8

	/// Write a line on `stdin` and wait for a prompt on stdout.
	///
	/// The `line` should contain the trailing newline.
	///
	/// The `find` parameter determines where the prompt can be found in the output line.
	#[instrument(skip(self, stdout), level = "debug")]
	async fn write_line_with_prompt_at(
	&mut self,
	stdout: &mut GhciStdout,
	line: &str,
	find: FindAt,
	log: &mut CompilationLog,
	) -> miette::Result<()> {
	self.stdin
	.write_all(line.as_bytes())
	.await
	.into_diagnostic()?;
	stdout.prompt(find, log).await
	}

[9999years]

@LightAndLight Would you open a new ticket for non-terminating applications? I'd really like to hear a proposed design, too, since I'm not sure how I'd implement that. (Maybe use something to save a binding corresponding to the async action...? But I think that various commands ghciwatch runs will clear bindings...)

[LightAndLight]

#325