Alternative (per-project) package database

[Dimitry Golubovsky]

Hi,

Summarizing my findings (I couldn't find solution to this problem
anywhere; maybe somebody else gets interested as well).

Experimental setting:

A simple package targeting a hello-world like application. We will
keep all dependent upon packages in a subdir named .private-pkg
All commands are run from within this project directory.

Bootstrapping:

Initialize packages database

ghc-pkg init .private-pkg

Clone few initial packages from the existing installation:

ghc-pkg describe <package name here> |
(GHC_PACKAGE_PATH=`pwd`/.private-pkg/ ghc-pkg register -)

These packages are (in this order): ffi, rts, ghc-prim, integer-gmp,
base-4.2.0.1 (or whatever base-4 you have)

If just "base" is specified, ghc-pkg will attempt to dump the
description of base-3.x.x.x package which is not what we need.

Check that packages are installed without problems.

$ GHC_PACKAGE_PATH=`pwd`/.private-pkg/ ghc-pkg list
/home/dima/src/hello-pvt/.private-pkg/
   base-4.2.0.1
   ffi-1.0
   ghc-prim-0.2.0.0
   integer-gmp-0.2.0.1
   rts-1.0

Try to install some package (for simplicity, choose `bytestring' as it
has only base in dependencies).

(export GHC_PACKAGE_PATH=`pwd`/.private-pkg/; cabal install bytestring
--package-db=$GHC_PACKAGE_PATH --prefix=`pwd`)

$ GHC_PACKAGE_PATH=`pwd`/.private-pkg/ ghc-pkg list
/home/dima/src/hello-pvt/.private-pkg/
   base-4.2.0.1
   bytestring-0.9.1.7
   ffi-1.0
   ghc-prim-0.2.0.0
   integer-gmp-0.2.0.1
   rts-1.0

Our test executable looks like this:

---------------------------------------------------------------------------
module Main where

import System.Directory

main = do
  putStrLn "Hello Private World"
  getDirectoryContents "." >>= putStrLn . show
---------------------------------------------------------------------------

So we have to include `directory' as dependency in the project's cabal
file. Let's build the executable:

(export GHC_PACKAGE_PATH=`pwd`/.private-pkg/; cabal install
--package-db=$GHC_PACKAGE_PATH --prefix=`pwd`)

Resolving dependencies...
Configuring filepath-1.1.0.4...
Preprocessing library filepath-1.1.0.4...
Building filepath-1.1.0.4...
[1 of 3] Compiling System.FilePath.Windows (
System/FilePath/Windows.hs, dist/build/System/FilePath/Windows.o )
[2 of 3] Compiling System.FilePath.Posix ( System/FilePath/Posix.hs,
dist/build/System/FilePath/Posix.o )
[3 of 3] Compiling System.FilePath  ( System/FilePath.hs,
dist/build/System/FilePath.o )
Registering filepath-1.1.0.4...
Installing library in /home/dima/src/hello-pvt/lib/filepath-1.1.0.4/ghc-6.12.2
...............................
Building directory-1.0.1.1...
[1 of 1] Compiling System.Directory ( System/Directory.hs,
dist/build/System/Directory.o )
Registering directory-1.0.1.1...
Installing library in
/home/dima/src/hello-pvt/lib/directory-1.0.1.1/ghc-6.12.2
Registering directory-1.0.1.1...
Configuring hello-pvt-0.1...
Preprocessing executables for hello-pvt-0.1...
Building hello-pvt-0.1...
Linking dist/build/hello-pvt/hello-pvt ...
Installing executable(s) in /home/dima/src/hello-pvt/bin
....................
$ GHC_PACKAGE_PATH=`pwd`/.private-pkg/ ghc-pkg list
/home/dima/src/hello-pvt/.private-pkg/
   base-4.2.0.1
   bytestring-0.9.1.7
   directory-1.0.1.1
   ffi-1.0
   filepath-1.1.0.4
   ghc-prim-0.2.0.0
   integer-gmp-0.2.0.1
   old-locale-1.0.0.2
   old-time-1.0.0.5
   rts-1.0
   unix-2.4.0.2

Thus, everything needed got compiled and installed under the project's
directory. So it will be easy to clean everything up just by removing
bin, lib, and .private-pkg subdirs (or choose a better prefix for
cabal install, so everything will install in a single location).

So, cabal does work in project-private mode. Maybe developers of
cabal-install would consider adding such mode to the program, so all
these extra options will not be needed. Of course votes from other
users will increase the chance of such addition ;)

Thanks.

-- 
Dimitry Golubovsky

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