specify nix integration options in stack.yaml

[ghost]

Resolves #668, possibly #669.
I was able to successfully build master using this stack.yaml and running the following:

$ stack --nix --no-nix-pure install

The nix-no-pure preserves LANG and other user environment variables so the documentation files will build successfully. It may be a better nix practice to use a shell.nix as outlined here to set the LANG explicitly. An example file is here

[simonmichael]

Great. I didn't know stack had special nix support.

As I was saying on #669, we'd like to make this just work when following standard install flow if possible. Those links look useful.

[simonmichael]

@efx can you explain why this fixes your issue ? Also why is it enable:false ?

[simonmichael]

I think:

• adding pure: false to the yaml file can replace --no-nix-pure
• adding a .nix file doesn't bring any benefit
• writing --nix on the command line is required for any of this to have an effect ?

[ghost]

@simonmichael

1. This fixed my issue because it caused the entire toolchain to build successfully on my Arch Linux environment. As you had mentioned before, Arch Linux seems to have some Haskell toolchain compilation woes. I did not get anywhere toggling various ~/.stack/config settings or installing things via Arch User Repositories. After I found the stack integration links, I ran with that solution and it caused the main compiles to just work.
2. If a nix section is specified it compiles things in the nix-shell by default. I am not familiar enough with GHCI and the impact on the build chain to make the call, so I opted for a less intrusive method. We could test the settings more and prefer by default if you don't see other problems doing so.
3. Correct, this requires passing --nix when running stack install.

[simonmichael]

I know it fixed your issue on Arch Linux, but I'm hoping we'll find out how/why it did, and the full effects of these changes. It might not be worth complicating our scripts for everyone if it's just a temporary Arch-specific issue, eg.

I see, enabled:true in stack.yaml would mean "always install with nix", while enabled:false means "install with nix if user specifies --nix on command line". Thanks.

[simonmichael]

Sorry, I have been getting confused by these nix-related discussions. This seems like a good improvement for folks using nix (enabled via --nix flag or in ~/.stack/config.yaml) and low impact on non-nix users. Thanks!

[ghost]

@simonmichael no problem! I totally understand the concern for impact on the broader user base. I will be happy to further contribute in getting something that works best across environments.
I think this could be improved still, as I realized I had to pass --nix when using the various make commands.