Add explicit type for stack.yaml location

[fendor]

Also, if no stack.yaml was given, don't default to "stack.yaml"

This also fixes a regression. Assume the following setup:

> cat File.hs
module File where

foo :: Int
foo = 2
> cat hie.yaml
cradle:
  stack:
> hie-bios check File.hs

This used to work, as we simply invoked stack repl to find the project arguments

[fendor]

cc @WorldSEnder might be interesting for you. Also, this is the only way I can ask for a review from you :)

[WorldSEnder]

That's a good catch, I didn't think about standalone stack projects. I suppose there should be a testcase to document the regression.

I have a question about the usage of prependIfRelative. I was under the expression that </> already handles this, by returning the second argument if it starts with a drive letter or directory separator. Is there some windows detail I'm missing? In any case, I think it would be worth to document this with a test case (in a different PR).

[fendor]

I was under the expression that </> already handles this

You seem to be right! Then this is an oversight, and this function should not exist at all. We should remove it. Thank you for mentioning this! I was not aware that this should work.

[WorldSEnder]

There are some subtle differences, if I read the documentation correctly (I don't have a windows system to test right now). For example, isRelative "c:test" == True but "D:\\foo" </> "C:bar" == "C:bar" (i.e. handled as if "c:bar" was absolute).

But I don't see an example where isAbsolute f and (wdir </> f) /= f, so I do believe prependIfRelative is superfluous.