get cabal repl working

[hhefesto]

Original Issue: sfultong/stand-in-language#16

: user specified .o/.so/.DLL could not be loaded (libjumper.so: cannot open shared object file: No such file or directory)
Whilst trying to load: (dynamic) jumper
Additional directories searched: (none)

[hhefesto]

on shell.nix having sil = super.callCabal2nix "sil" ./. { gc = pkgs.boehmgc; jumper = sil_jumper; };
the cabal new-repl error is:

[nix-shell:~/src/stand-in-language]$ cabal new-repl
Build profile: -w ghc-8.6.5 -O1
In order, the following will be built (use -v for more details):
 - sil-0.1.0.0 (lib) (first run)
Preprocessing library for sil-0.1.0.0..
GHCi, version 8.6.5: http://www.haskell.org/ghc/  :? for help
<command line>: user specified .o/.so/.DLL could not be loaded (libgc.so: cannot open shared object file: No such file or directory)
Whilst trying to load:  (dynamic) gc
Additional directories searched: (none)
cabal: repl failed for sil-0.1.0.0.

using sil = super.callCabal2nix "sil" ./. { jumper = sil_jumper; }; instead gives a similar error with an extra of cabal not being updated:

[nix-shell:~/src/stand-in-language]$ cabal new-repl
Warning: The package list for 'www.stackage.org' is 103 days old.
Run 'cabal update' to get the latest list of available packages.
Resolving dependencies...
Build profile: -w ghc-8.6.5 -O1
In order, the following will be built (use -v for more details):
 - sil-0.1.0.0 (lib) (configuration changed)
Configuring library for sil-0.1.0.0..
Preprocessing library for sil-0.1.0.0..
GHCi, version 8.6.5: http://www.haskell.org/ghc/  :? for help
<command line>: user specified .o/.so/.DLL could not be loaded (libgc.so: cannot open shared object file: No such file or directory)
Whilst trying to load:  (dynamic) gc
Additional directories searched: (none)
cabal: repl failed for sil-0.1.0.0.

So it might be that the missing gc complaint comes from sil-jumper

[hhefesto]

by the way. Originally the issue says that

Whilst trying to load: (dynamic) jumper

but I get
Whilst trying to load: (dynamic) gc

[sfultong]

ghci doesn't know where to look for the right shared libraries. Maybe cabal isn't passing them in correctly or something.

so somehow we have to add to the ghci shared library path (maybe set the LD_LIBRARY_PATH environment variable? That's probably too easy)

[hhefesto]

Solved it, but not elegantly:

So pkgs.bohemgc provides libgc.so.1

I copied libgc.so.1 into a new lib directory in the root of the git repo (in my case, inside of the nix-shell, I found libgc.so.1 by running ldd `which nix` ), renamed it to libgc.so, and referenced it in sil.cabal

There should be a more elegant solution using Nix.

[hhefesto]

to reference it on sil.cabal I added extra-lib-dirs: lib under the library stanza

[hhefesto]

by adding extra-lib-dirs: lib there are two effects:
cabal new-repl works
cabal new-build fails

to get cabal build to work again, comment the extra-lib-dirs line, re-enter nix-shell and run cabal new-build

[hhefesto]

by adding extra-lib-dirs: lib there are two effects:
cabal new-repl works
cabal new-build fails

to get cabal build to work again, comment the extra-lib-dirs line, re-enter nix-shell and run cabal new-build

This is solved by giving complete path to extra-lib-dirs.

In my case:

library
  ...
  extra-lib-dirs:      /home/hhefesto/src/stand-in-language/lib

[hhefesto]

Might be able to have nix-shell sed replace a placeholder and put the appropriate extra-lib-dirs whole route (as needed).

Gitter:

@sfultong
Jul 10 15:37
oh, apparently there is a way to run a command when you enter a nix shell
https://nix.dev/tutorials/declarative-and-reproducible-developer-environments.html
see shellHook