Question: custom GHC path in stack.yaml?

[rpglover64]

Is there a way to tell stack to use GHC at a specific location for a project? I don't want to put it on the path every time I run stack for that project.

[snoyberg]

No, there's no such functionality right now. The primary concern I'd have is that it would make your project tied to a specific machine's configuration.

[rpglover64]

Makes sense. It would be bad practice for release, but I think it's still useful for development.

With cabal, I could put it in a cabal.config file at the with-compiler field.

It also occurs to me that if I want to use a GHC installed at a non-standard location for all my projects, I could symlink it to where stack searches for its personal copies if I knew the exact naming scheme.

My specific usecase is that I want to use a patched 7.10.2 to build stackage nightlies and eventually LTS.

[snoyberg]

Got reminded on Reddit about this: I should have pinged this issue when #798 got merged to master, which will allow you to do something like:

extra-path:
- /path/to/ghc/bin

[rpglover64]

Awesome. I think that solves my problem.

[nh2]

I had to do this to make stack pick up my custom ghc I built from the ghc source dir:

First in my ghc source dir, cd inplace/bin && ln -s ghc-stage2 ghc to make sure my ghc executable is available as ghc.

Then in stack.yaml of the project I want to compile with my custom ghc:

extra-path:
- /path/to/ghc/checkout/inplace/bin

system-ghc: true
skip-ghc-check: true

Note: This is only for when you're hacking on GHC incrementally. If you just want to use a different bindist, see How to use different ghc builds with stack?.

[osa1]

Is there a better way to do this these days or is the comment above still the best option?

[mgsloan]

@osa1 I believe the above comment is still the best option. A more general solution to this sort of thing is tracked by #2369

[jberryman]

Trying @nh2 's technique and getting linker error partway through a big cabal build

2019-02-26 11:25:36.340359: [info] lens-4.17: configure (lib)
2019-02-26 11:25:36.341619: [debug] Run process within /home/me/Code/BOLT-experiments/lens-4.17/: /home/me/Code/NOT_MY_CODE/ghc/inplace/bin/ghc-stage2 --make -odir /home/me/Code/BOLT-experiments/lens-4.17/.stack-work/dist/x86_64-linux/Cabal-2.4.0.1/setup -hidir /home/me/Code/BOLT-experiments/lens-4.17/.stack-work/dist/x86_64-linux/Cabal-2.4.0.1/setup -i -i. -clear-package-db -global-package-db -package-db=/home/me/.stack/snapshots/x86_64-linux/lts-13.5/8.6.3/pkgdb -package-db=/home/me/Code/BOLT-experiments/.stack-work/install/x86_64-linux/lts-13.5/8.6.3/pkgdb -hide-all-packages -package-id=Cabal-2.4.1.0-IaB5GUEm19R82R9cEdbB1D -package-id=base-4.12.0.0 -package-id=cabal-doctest-1.0.6-86ieqb3MUgY7IBnRw4OXav -package-id=filepath-1.4.2.1 -optP-include -optP/home/me/Code/BOLT-experiments/lens-4.17/.stack-work/dist/x86_64-linux/Cabal-2.4.0.1/setup/setup_macros.h /home/me/Code/BOLT-experiments/lens-4.17/Setup.lhs /home/me/.stack/setup-exe-src/setup-shim-mPHDZzAJ.hs -main-is StackSetupShim.mainOverride -o /home/me/Code/BOLT-experiments/lens-4.17/.stack-work/dist/x86_64-linux/Cabal-2.4.0.1/setup/setup -threaded
2019-02-26 11:25:36.487033: [info] [1 of 2] Compiling Main             ( /home/me/Code/BOLT-experiments/lens-4.17/Setup.lhs, /home/me/Code/BOLT-experiments/lens-4.17/.stack-work/dist/x86_64-linux/Cabal-2.4.0.1/setup/Main.o )
2019-02-26 11:25:36.592745: [info] [2 of 2] Compiling StackSetupShim   ( /home/me/.stack/setup-exe-src/setup-shim-mPHDZzAJ.hs, /home/me/Code/BOLT-experiments/lens-4.17/.stack-work/dist/x86_64-linux/Cabal-2.4.0.1/setup/StackSetupShim.o )
2019-02-26 11:25:36.744372: [info] Linking /home/me/Code/BOLT-experiments/lens-4.17/.stack-work/dist/x86_64-linux/Cabal-2.4.0.1/setup/setup ...
2019-02-26 11:25:38.016434: [warn] /home/me/.stack/snapshots/x86_64-linux/lts-13.5/8.6.3/lib/x86_64-linux-ghc-8.6.3/Cabal-2.4.1.0-IaB5GUEm19R82R9cEdbB1D/libHSCabal-2.4.1.0-IaB5GUEm19R82R9cEdbB1D.a(Configure.o)(.text+0xa379): error: undefined reference to 'base_GHCziIOziException_zdfExceptionIOException4_closure'
2019-02-26 11:25:38.016565: [warn] /home/me/.stack/snapshots/x86_64-linux/lts-13.5/8.6.3/lib/x86_64-linux-ghc-8.6.3/Cabal-2.4.1.0-IaB5GUEm19R82R9cEdbB1D/libHSCabal-2.4.1.0-IaB5GUEm19R82R9cEdbB1D.a(Configure.o)(.text+0xa919): error: undefined reference to 'base_GHCziIOziException_zdfExceptionIOException4_closure'
2019-02-26 11:25:38.016622: [warn] /home/me/.stack/snapshots/x86_64-linux/lts-13.5/8.6.3/lib/x86_64-linux-ghc-8.6.3/Cabal-2.4.1.0-IaB5GUEm19R82R9cEdbB1D/libHSCabal-2.4.1.0-IaB5GUEm19R82R9cEdbB1D.a(Configure.o)(.text+0x2d1e1): error: undefined reference to 'base_GHCziIOziException_zdfExceptionIOException4_closure'
2019-02-26 11:25:38.016678: [warn] /home/me/.stack/snapshots/x86_64-linux/lts-13.5/8.6.3/lib/x86_64-linux-ghc-8.6.3/Cabal-2.4.1.0-IaB5GUEm19R82R9cEdbB1D/libHSCabal-2.4.1.0-IaB5GUEm19R82R9cEdbB1D.a(Configure.o)(.data+0x5468): error: undefined reference to 'base_GHCziIOziException_zdfExceptionIOException4_closure'
2019-02-26 11:25:38.017922: [warn] collect2: error: ld returned 1 exit status
2019-02-26 11:25:38.018562: [warn] `gcc' failed in phase `Linker'. (Exit code: 1)

[nh2]

@jberryman Can you clean and rebuild just to make sure you aren't suffering from .o file corruption?

Also, which of the two techniques I mentioned are you using the one for

hacking on GHC incrementally

or the other one?

[jberryman]

@nh2 sorry, yes "hacking on ghc". Yeah I've tried clean --full, as well as setting extra-lib-dirs to inplace/lib/.

[nh2]

@jberryman Hmm, then I'm not sure, especially given that you apparently have a missing symbol in something as basic as GHC.Exception, but it pops up only as late as lens.

[jberryman]

Thanks it's a multiproject stack repo with some random libraries stack unpack-ed into it (including lens). I edited my original post above with better output.

I wonder if you can repro with stack unpack lens-4.17 && stack build lens.

It seems to be related to lens's use of a custom-setup section in the lens cabal file. If I remove that section I can build the library successfully. EDIT: although now I'm getting a similar error during configure on shakespeare which uses a build-type: Simple...

Appreciate the tip. I'm going to move on for now, and don't want to clutter this ticket anymore.

EDIT2: I wonder if it has something to do with the ordering of package dbs (inplace ghc's are last):

stack/src/Stack/GhcPkg.hs

Line 181 in 3bb2a02

mkGhcPackagePath :: Bool -> Path Abs Dir -> Path Abs Dir -> [Path Abs Dir] -> Path Abs Dir -> Text

[nh2]

@jberryman I care about this workflow working, so I'd be happy to help with it.

But can you make me some detail instructions on what to do?

I wonder if you can repro with stack unpack lens-4.17 && stack build lens.

With what exact stack.yaml?