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- We don't support Cabal's
new-buildyet :( - You need to recompile ghc-mod when you change GHC versions, just run
cabal install ghc-modagain and you're good. We are working on a permanent fix for this, see ghc-mod Issue: Implement worker/wrapper split, support multiple GHC versions.
Make sure the dist/setup-config file doesn't exist in your project directory (the directory also containing your *.cabal file). When this file exists ghc-mod assumes you want to use cabal-install instead of Stack.
Most ghc-mod+Stack issues have to do with a GHC version mismatch.
ghc-mod once compiled is bound to one version of GHC since we link against the GHC API library. This used to not be a very big problem but since Stack made it exceedingly easy to use more than one version of GHC without even realising.
Many users report success with starting their editors/IDEs or shells with stack exec inside the project they are working on after installing ghc-mod locally
inside that project, for example:
$ cd my/super/cool/project/
$ stack install ghc-mod
$ stack exec -- emacs
The install command only needs to be run once unless you want to upgrade the
ghc-mod version in use for that project. The stack exec command will run Emacs
(or your editor of choice) with a modified environment which (among other
things) adds the project-local binary installation directory to PATH.
ghc-mod: $HOME/.stack/snapshots/x86_64-linux/lts-2.22/7.8.4/pkgdb/package.cache: GHC.PackageDb.readPackageDb: inappropriate type (not a ghc-pkg db file, wrong file magic number)
Your Stack resolver uses a different GHC version from what ghc-mod was linked with, in this case:
$ ghc-mod --version
ghc-mod version 5.3.0.0 compiled by GHC 7.10.2
VS.
$ stack ghc -- --version
The Glorious Glasgow Haskell Compilation System, version 7.8.4
You need to recompile ghc-mod using GHC version 7.8.4 to fix this. Note that you can use the cabal install option --program-suffix=SUFFIX to append a GHC version number to ghc-mod's executable name so you can keep multiple copies of ghc-mod around without recompiling. There is no frontend support for automatically switching to the right executable though so you'll have to manage that manually using symlinks or a wrapper script. See also ghc-mod Issue: Support switching GHC versions without recompiling
ghc-mod: <command line>: cannot satisfy -package-id aeson-0.10.0.0-a37a650f6e5d5ca2347967c8f8609dfd:
aeson-0.10.0.0-a37a650f6e5d5ca2347967c8f8609dfd is unusable due to missing or recursive dependencies:
attoparsec-0.13.0.1-9f9155916734a226d3befd6aaf235548 base-4.8.2.0-0d6d1084fbc041e1cded9228e80e264d <...>
(use -v for more information)
Same root cause as above: readPackageDb: inappropriate type.
Failed to load interface for ‘Some.Module’ There are files missing in the ‘package-1.2.3’
package,try running 'ghc-pkg check'
Same root cause as above: readPackageDb: inappropriate type.
Full error message:
cabal-helper-wrapper: ghc: readCreateProcess: runInteractiveProcess: exec: does not exist (No such file or directory)
cabal-helper needs a working ghc executable at runtime to build it's wrapper component, when using only Stack's builtin GHC there is no ghc on $PATH hence this error.
To fix this simply add one of the paths in the output of the following command to your $PATH environment variable.
printf '%s\n' ~/.stack/programs/*/ghc-*/bin/