Ghc-pkg cannot unregister/expose/hide packages in non-first package databases

[batterseapower]

I was in this situation:

$ ghc-pkg list
/usr/local/lib/ghc-6.8.2/package.conf:
    Cabal-1.2.3.0, Cabal-1.5.1, Finance-Quote-Yahoo-0.4.1,
    GLUT-2.1.1.1, HTTP-3001.0.4, HTTP-Simple-0.1, HUnit-1.2.0.0,
    OpenAL-1.3.1.1, QuickCheck-1.1.0.0, array-0.1.0.0, base-3.0.1.0,
    binary-0.4.1, bytestring-0.9.0.1, cgi-3001.1.5.1,
    containers-0.1.0.1, directory-1.0.0.0, fgl-5.4.1.1,
    filepath-1.1.0.0, (ghc-6.8.2), haskell-src-1.0.1.1,
    haskell98-1.0.1.0, hpc-0.5.0.0, html-1.0.1.1, hxt-7.4, mtl-1.1.0.0,
    network-2.1.0.0, old-locale-1.0.0.0, old-time-1.0.0.0,
    packedstring-0.1.0.0, parallel-1.0.0.0, parsec-2.1.0.0,
    plugins-1.0, plugins-1.1, pretty-1.0.0.0, process-1.0.0.0,
    random-1.0.0.0, readline-1.0.1.0, regex-base-0.72.0.1,
    regex-compat-0.71.0.1, regex-posix-0.72.0.2, rts-1.0, stm-2.1.1.0,
    template-haskell-2.2.0.0, time-1.1.2.0, unix-2.3.0.0,
    xhtml-3000.0.2.1, zlib-0.4.0.4
/Users/mbolingbroke/.ghc/i386-darwin-6.8.2/package.conf:
    Cabal-1.4.0.0, GLUT-2.1.1.1, HDBC-1.1.4, MaybeT-0.1.1,
    MonadRandom-0.1.1, OpenGL-2.2.1.1, Stream-0.2.3, arrows-0.4,
    category-extras-0.53.4, haddock-2.1.0

And from there I can do this:

$ ../../../../ghc.plugins/utils/ghc-pkg/ghc-pkg-inplace describe pan-plugin-annotations
name: pan-plugin-annotations
version: 1.0
license: BSD3
copyright: (c) Sean Seefried 2008
maintainer: sseefried@cse.unsw.edu.au
stability: stable
homepage:
...

But not this!

$ ../../../../ghc.plugins/utils/ghc-pkg/ghc-pkg-inplace expose pan-plugin-annotations-1.0
ghc-pkg-inplace: cannot find package pan-plugin-annotations-1.0

Or this:

$ ../../../../ghc.plugins/utils/ghc-pkg/ghc-pkg-inplace hide pan-plugin-annotations-1.0
ghc-pkg-inplace: cannot find package pan-plugin-annotations-1.0

The reason is that ghc-pkgs modifyPackage function only looks in the FIRST package database in the list. In my opinion, it should look in all databases and either:

1. Perform the modification requested by the user to the first database that contains the relevant package

2. Show a smart error message indicating to the user that they need to use some flags to bring that package to the front of the package stack if they want to do that, rather than just saying "not found"

I've attached a patch that implements behaviour 1.

[batterseapower]

Patch implementing behaviour 1

[duncan]

Similarly we notice in #haskell that frequently people are very confused by ghc-plg list saying that a package is installed but then unregistering fails (because they do not understand the --user issue). This confusion is on the rise because cabal-install now does per-user installs by default which means there are more people with per-user packages registered and since they never had to use the --user flag in the first place they are unaware of the whole concept of global vs user package dbs..

Either different default behaviour or a better error message would be an improvement. For example at least the error message should note that the package is in the --user db and that if they should use that flag.

[simonmar]

Fixed. I modified the submitted patch to do the right thing, and fixed up some other bogosity that I found along the way. Also I added a test to the testsuite.

Thu Aug 14 13:53:48 BST 2008  Simon Marlow <marlowsd@gmail.com>
  * Fix #2441 (unregister/expose/hide packages in non-first package databases)