Allow "--ghc-options -hpcdir" to be selectively disabled via CLI

[adinapoli]

Hello folks,

first of all I'm not expecting this to be considered a stack issue, as I'm not sure it is. I'm writing this down as this project is highly maintained and having this kind of reports might help others in the future. I have ported a snap project I have at work to use stack. So far so good, pretty much smooth sailing. If you are not familiar with snap it supports automatic recompilation leveraging hint. I have therefore enabled the "dev" mode calling:

stack install --flag chronos:development

Which built just fine. Upon startup though, I realised that hint was trying to look for packages in my global package index and, unable to find my deps, was failing. This is similar to an issue someone reported here:

http://hub.darcs.net/jcpetruzza/hint/issue/5

Dutifully, I tried something like this:

GHC_PACKAGE_PATH=$(stack path --local-pkg-db) chronos

Which generated:

o port specified, defaulting to port 8000
Listening on http://0.0.0.0:8000/
chronos: Unknown interpreter error:

flags: '-hpcdir .stack-work/dist/x86_64-osx/Cabal-1.18.1.5/hpc/.hpc/' not recognized

And this is because - I suspect - stack is passing such flag dowstream and Hint's interpreter code is choking on it. Is Hint right here?

The project seems quite abandoned (but I might be totally wrong!) and unless someone knows better than me Snap's plan for 1.0 release, they seems to still leverage hint for automatic recompilation. This means this problem will hinder Stack's adoption for people using Snap.

Of course if I have missed something completely trivial and/or Snap is ditching hint in 1.0 I guess this issue is moot, but I thought would have been useful to share anyway!

Alfredo

[snoyberg]

I wouldn't see a problem with modifying stack such that it only sets that flag when actually doing coverage builds, but I could be mistaken (@mgsloan, could you weigh in?).

@adinapoli would you be up for sending a PR to make that change?

[adinapoli]

@snoyberg Happy to do that, if @mgsloan says 👍

[snoyberg]

As a side note, it may be interesting to see if Snap applications work with https://github.com/urbanslug/wai-devel

[mgsloan]

Sounds good to me! You'll probably want to pass in BuildOpts to extraBuildOptions. Then, toCoverage (boptsTestOpts bopts) tells you if coverage is enabled.