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