"inappropriate type (not a ghc-pkg db file)"

[thomasjm]

I run stack ide start in my project and I get the following error:

{"tag":"ResponseWelcome","contents":[0,1,1]}
{"tag":"ResponseUpdateSession","contents":{"tag":"UpdateStatusCrashRestart","contents":"External exception: /Users/tomm/.stack/snapshots/x86_64-osx/lts-2.16/7.8.4/pkgdb/package.cache: GHC.PackageDb.readPackageDb: inappropriate type (not a ghc-pkg db file, wrong file magic number). Local exception: user error (IdeSession.RPC.Stream ended, causing demandInput: not enough bytes)"}}

[mgsloan]

My guess is that the ide-backend-server on your path is using a newer version of GHC. ResponseWelcome really ought to give more info about GHC versions and such. I've created this issue to track that: #43

stack ide does not yet streamline making sure that the right version of ide-backend-server is used, and does not yet automate its installation. So for now, that part of things is manual. Relevant stack issue: commercialhaskell/stack#662

If I'm right about the cause, there are two approaches to resolve this:

• Run stack --stack-yaml=stack-7.8.yaml install in the ide-backend or stack-ide repo. This will install a version that uses ghc 7.8.
• Run stack install in the ide-backend or stack-ide repo. Update your project to use a very recent nightly resolver (such as nightly-2015-08-06), so that you're using ghc-7.10.2 for your project.

(NOTE: you'll also want to pull both of these repos, I updated all the stack.yaml resolvers a few minutes ago)

[thomasjm]

You're right about that, ide-backend-server was installed with GHC 7.10 but my project uses GHC 7.8. I upgraded my project to use 7.10 as well and it worked. Thanks!

[erikkaplun]

How about if I need the project to use GHC 7.8.x? I also have another project that needs GHC 7.10.x.

So is there currently no way to use stack-ide on projects with different GHC versions?