Building GHC using cabal repl

[Joachim Breitner]

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 joachim-breitner.de
  https://www.joachim-breitner.de/
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