The package database should be a directory of files instead of a single file

[simonmar]

This would help package systems that want to install packages by just unpacking a bunch of files onto the filesystem, amongst other things.

See:  http://www.haskell.org//pipermail/glasgow-haskell-users/2006-March/009838.html

[simonmar]

Comments from Duncan Coutts:

One downside to using a dir approach is that it makes it harder to optimise the format of these files (since they do take a little while to parse).

One could use a binary format for the installed files, but it still means opening several small files. That's probably the sweet-spot for performance/effort. It might be possible to keep the package.conf files in the nice cabal text formal and then build a cache. However it's not obvious where such a cache would go. It could go in the users ~/.ghc directory but that will not work well for the root user. For example on gentoo and debian updating such a cache would cause a sandbox violation during a build.

So for example we could use ghc-pkg to install into a given package db dir and it could write the binary format file:

ghc-pkg register foo.pkg -f buildtmp/package.conf.d/ --force

On a related note, we sadly have to use --force in this instance since we're installing into a temp dir so the directories do not exist yet in the real root file system. We could avoid --force with {{{--pkg-root= ${DESTDIR}}}} or something, but it'd need more complexity in ghc-pkg.

[greenrd@…]

I'm packaging Haskell stuff for rPath Linux, and I'm going to look into implementing at least the splitting out part of this task.

[simonmar]

See also #593

[simonmar]

The package DB is now a directory of files by default (the old text-file format is still supported).

Thu Sep 10 03:27:03 PDT 2009  Simon Marlow <marlowsd@gmail.com>
  * Change the representation of the package database
  Ignore-this: 7c9b38ded7f753d5bb95743695700dbc
  
   - the package DB is a directory containing one file per package
     instance (#723)
  
   - there is a binary cache of the database (#593, #2089)
  
   - the binary package is now a boot package
  
   - there is a new package, bin-package-db, containing the Binary
     instance of InstalledPackageInfo for the binary cache.
  
  Also included in this patch
  
   - Use colour in 'ghc-pkg list' to indicate broken or hidden packages
    
     Broken packages are red, hidden packages are 
    
     Colour support comes from the terminfo package, and is only used when
      - not --simple-output
      - stdout is a TTY
      - the terminal type has colour capability
  
   - Fix the bug that 'ghc-pkg list --user' shows everything as broken