[DUX-2916] Single file with `--enable-eval` errors

[cideM]

What happened?

Given this file foo.hs

myGreeting :: String
myGreeting = "Hello"

-- $> putStrLn (myGreeting <> " " <> myGreeting)

I get the following output

❯ ghciwatch foo.hs --enable-eval --clear
GHCi, version 9.6.6: https://www.haskell.org/ghc/  :? for help
[1 of 2] Compiling Main             ( foo.hs, interpreted )
Ok, one module loaded.
• All good! Finished starting up in 6.09s
• foo.hs:4:7: putStrLn (myGreeting <> " " <> myGreeting)
[1 of 2] Compiling Main             ( foo.hs, interpreted )
Ok, one module loaded.
Error:   × Tasks failed:
  │ • run_ghci: Couldn't convert /Users/fbs/private/advent_of_code/aoc2024-haskell/foo to
  │ module name

What did you expect to happen?

See the output from the example:

• src/MyLib.hs:9:7: putStrLn (myGreeting <> " " <> myGreeting)
Hello Hello

Steps to reproduce the issue

No response

The version of ghciwatch with the bug

ghciwatch 1.0.2

_DUX-2916

[9999years]

Thanks for the report! Looks like ghciwatch is trying to convert foo.hs to a module name in the GHCi search paths, which isn't working because we're not in a cabal project.

Related: #69, #238

Not sure how easy this would be to fix, but you're welcome to take a stab at it. Maybe the :module + *MODULE_NAME syntax doesn't work with paths? If it's not possible to make that work, there's a few options:

• Print a warning explaining why it won't work instead of failing the whole program.
• Maybe print a warning explaining that unexported top-level bindings won't be available and skip the :module + *MODULE_NAME command?

Here's the responsible code:

ghciwatch/src/ghci/mod.rs

Lines 571 to 584 in 2d61403

	// If the `module` was already compiled, `ghci` may have loaded the interface file instead
	// of the interpreted bytecode, giving us this error message when we attempt to
	// load the top-level scope with `:module + *{module}`:
	//
	// module 'Mercury.Typescript.Golden' is not interpreted
	//
	// We use `:add *{module}` to force interpreting the module. We do this here instead of in
	// `add_module` to save time if eval commands aren't used (or aren't needed for a
	// particular module).
	self.interpret_module(&path, log).await?;
	let module = self.search_paths.path_to_module(&path)?;
	self.stdin
	.eval(&mut self.stdout, &module, &command.command, log)
	.await?;

ghciwatch/src/ghci/stdin.rs

Line 159 in 2d61403

self.write_line(stdout, &format!(":module + *{module_name}\n"), log)