wiki:Debugging/InstallingPackagesInplace

Version 21 (modified by domtheo, 11 months ago) (diff)

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Installing packages in your test compiler

You have your compiler built, so you can use the inplace compiler to compile test programs. This lives in $(TOP)/inplace/bin/ghc-stage2 (see Commentary/SourceTree).

Every GHC, including the inplace one, comes with the boot libraries. But sometimes a test case will require the installation of some packages from Hackage. There are two routes.

Plan A: use cabal install

This method is quick and easy, but can fail if your cabal program is out of date with respect to the GHC version you are building. Here's how to install a library against a GHC build tree:

cabal install --with-compiler=<inplace-ghc> <package>

where <inplace ghc> is the path to your inplace GHC (usually $(TOP)/inplace/bin/ghc-stage2; make sure it's absolute), and <package> is the name of the package.

Points to note:

  • This will install the package in your home directory (e.g. somewhere under ~/.cabal/lib on a Unix system), and it will register the package in your private package database, so you'll probably want to remove and unregister it by hand when you've finished.

Plan A can fail, because sometimes GHC changes require corresponding Cabal changes (this happened in GHC 6.12, and after the GHC 7.6.1 release). If the format changed you might get a message like

cabal: failed to parse output of 'ghc-pkg dump'

But incompatibility can result in other problems installing packages. In that case you need to use the Cabal code that comes with the new version of GHC (ie the one in your build tree). So use Plan B.

Plan B: use the Cabal library bundled with GHC

This method is slightly more work, but it does have the advantage of not installing anything in your home directory that you have to go and remove later.

Go to a directory where you are happy to keep the newly-downloaded code.

cabal unpack <package>
cd <package>
<inplace-ghc> --make Setup.lhs
./Setup configure --with-ghc=<inplace-ghc> --global
./Setup build
./Setup register --inplace

Points to note here:

  • The first step can be done manually, by downloading a zip file from Hackage, or by doing grabbing the source from the appropriate repository. For example:
    darcs get http://darcs.haskell.org/packages/parallel
    
    Nevertheless, cabal unpack should work for any Hackage package, even if Cabal has changed a bit. (Because fetching and unpacking is one of Cabal's less sophisticated operations.)
  • It is important to compile Setup.lhs with your shiny new inplace GHC, not your installed GHC. Your inplace GHC has the most up-to-date Cabal library, and that is what you want to link Setup.lhs against.
  • The --global flag instructs Cabal to register the package in the database in your build tree, rather than the one in your home directory (~/.ghc/...). In fact, --global is actually unnecessary (it's the default), but just in case the default changes in the future it's a good idea to get in the habit of saying whether you want --global or --user.

  • The --inplace flag to register tells Cabal not to copy the compiled package, but rather to leave it right where it is, and register this location in the package database in your GHC build tree.

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