Building GHC using cabal repl

Moritz Angermann moritz at
Tue Apr 3 01:45:18 UTC 2018

Hi Joachim,

I believe this might be due to the recent changes
that try to keep the source tree pristine instead
of generating data in-place.  This is partially
the result of making ghc relocatable: hadrian#445[1].
It included changes to cabal and ghc and the final
bits have been merged in the form of hadrian#531[2]
just a few days ago into hadrian.  The make based
build system does not take advantage of this.

As `Config.hs` is a generated file it no resides in
the build folder; as such I believe your changes to
be correct.

Does hadrian have a load all of ghc into ghci?  I'm
afraid I don't think it does yet. I've opened
hadrian#551[3] for this.



> On Apr 2, 2018, at 11:50 PM, Joachim Breitner <mail at> wrote:
> Hi,
> when hacking on most Haskell projects these days, I enjoy having a
> shell with
>   ghcid -c 'cabal new-repl -w ghc-8.2'
> open. I wondered if I can achieve the same when hacking on GHC. The
> compiler/ directory has a Cabal file.
> It does not work out-of-the box (in a fully built tree):
>   $ cabal new-repl -w ../inplace/bin/ghc-stage2  -fstage2
>   Build profile: -w ghc-8.5.20180320 -O1
>   In order, the following will be built (use -v for more details):
>    - ghc-8.5 (lib) (first run)
>   Preprocessing library for ghc-8.5..
>   cabal: can't find source for Config in backpack, basicTypes, cmm, codeGen,
>   coreSyn, deSugar, ghci, hsSyn, iface, llvmGen, main, nativeGen, parser,
>   prelude, profiling, rename, simplCore, simplStg, specialise, stgSyn, stranal,
>   typecheck, types, utils, vectorise,
>   /home/jojo/build/haskell/ghc/compiler/dist-newstyle/build/x86_64-linux/ghc-8.5.20180320/ghc-8.5/build/autogen,
>   /home/jojo/build/haskell/ghc/compiler/dist-newstyle/build/x86_64-linux/ghc-8.5.20180320/ghc-8.5/build/global-autogen
>   cabal: repl failed for ghc-8.5.
> It seems that the stage2/build directory is not registered as a source
> directory:
>   $ find -name Config.hs
>   ./stage2/build/Config.hs
>   ./stage1/build/Config.hs
> But if I extend the section
>        if flag(stage2)
>            Include-Dirs: stage2
> with these lines
>            Include-Dirs: stage2/build
>            hs-source-dirs: stage2/build
>            ghc-options: -DSTAGE=2
>            ghc-options: -fobject-code
> and call cabal like so, it actually works:
>   cabal new-repl -w ../inplace/bin/ghc-stage2  -fstage2
> If I now make hdevtools use this line, then hacking on GHC will have a
> bit less friction…
> (BTW, does Hadrian have a “load all of GHC in GHCi” mode?)
> Cheers,
> Joachim
> -- 
> Joachim “nomeata” Breitner
>  mail at
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> ghc-devs at

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