Problem within repl in a stack project with multiple packages.

[meditans]

Hi, I have three undesired behaviours when using a repl in a stack project which makes use of a package on github in the packages section (in my case, a modified version of the hint package).

Firstly, I get this behaviour with stack ghci, or using haskell-mode inside emacs: When loading the package (eg. stack ghci) I get a lot of errors like this one:

In file included from <command-line>:10:0: /home/meditans/code/haskell/provaHint/.stack-work/downloaded/0075423eecf6de8b6352671754046c16f71edae18522ac5564debf553494bcea.git/.stack-work/dist/x86_64-linux/Cabal-1.22.4.0/build/autogen/cabal_macros.h:171:0: …
     warning: "CURRENT_PACKAGE_KEY" redefined
     #define CURRENT_PACKAGE_KEY "hint_KPuxWkEhUYP3oLnQwZzhof"
     ^

Secondly, inside emacs, I don't seem to be able to use ghc-mod, because of:

cannot satisfy -package-id hint-0.4.2.3-5d4875935ddea3fc0ae920904280faf4

Thirdly, as I am using a modified version of hint, a source code interpreter, the code of my program is unable to analyze imports outside of base, like Control.Lens, while the same program using the unmodified hint package could.

Is there a way to correct or mitigate these (probably interconnected) problems?

[mgsloan]

My guess is that this is caused by having cabal_macros.h from multiple packages. The best way to mitigate stuff like this is to run stack ghci on just one target. For example, stack ghci my-package:lib.

What's your stack version? Do these issues persist if you stack upgrade --git to use the current development version?

[PierreR]

I have the exact same problem when using a local package, though I cannot pinpoint exactly what triggers it.

[creichert]

I have this problem as well with no luck finding the root cause. It would be a big deal for my team if it was fixed since we have a hard time using ghci with stack at all. FWIW, the problematic project has a lot of git dependencies.

@mgsloan that suggestion works but is more difficult to use from an an editor (emacs). I think other issues arise when using stack ghci my-package:lib and trying to load files from another project.

I'll upgrade and try to provide some version numbers if the problem persists.

[mgsloan]

@creichert It might be helpful to put extra-dep: True on those git dependencies - see #1217

Most of the problems come from attempting to use ghci on multiple packages at once, which isn't really a very principled thing to do. See this ghc ticket on the subject: https://ghc.haskell.org/trac/ghc/ticket/10827

There may still be some bugs where stack could invoke ghci with a better options, but in general loading multiple packages / components is just something that can work, but there are numerous things that can break it.

The default behavior of stack ghci is to try to load everything, which is the most likely to not not work. Maybe stack ghci should just run ghci without loading any local packages.

For editor integration, maybe it would be useful to have stack ghci some/file/Path.hs, which will determine the cabal component to load based on the filepath.

[meditans]

@mgsloan I was using the latest stack, and the issue persisted after the upgrade to the git version.

However, all my issues were fixed adding extra-dep: True. I didn't know about that option, I think it would be useful to add it in the Stack guide!

[mgsloan]

Sounds like everyone's problems are resolved, closing. Feel free to open other issues about this stuff.