[Haskell-cafe] some problem with Cabal

[Daniel Fischer]

On Wednesday 09 March 2011 02:51:35, qiqi wrote:
> I used cabal install xmobar --flags="all_extensions" .

Whoa:

In order, the following would be installed:
containers-0.3.0.0 (new version)
filepath-1.1.0.4 (new version)
directory-1.1.0.0 (reinstall) changes: filepath-1.2.0.0 -> 1.1.0.4
hinotify-0.3.1 (new package)
mtl-1.1.1.1 (new version)
network-2.2.1.10 (new version)
process-1.0.1.5 (reinstall) changes: filepath-1.2.0.0 -> 1.1.0.4
stm-2.2.0.1 (new package)
syb-0.3 (new package)
X11-1.5.0.0 (new package)
time-1.1.4 (new version)
random-1.0.0.3 (reinstall) changes: time-1.2.0.3 -> 1.1.4
haskell98-1.1.0.1 (reinstall)
utf8-string-0.3.6 (new package)
X11-xft-0.3 (new package)
libmpd-0.5.0 (new package)
xmobar-0.12 (new package)

I haven't looked further, but libmpd is at least partially responsible, it 
depends on filepath < 1.2, time < 1.2 and a couple other old packages.

> Is it true that every package installed from hackage should not install
> any package, which already exists in the global with the same version
> number , in the local db?

Generally, it shouldn't (and doesn't), but here some packages have to be 
reinstalled because they have to be built against different dependencies.

I'd prefer cabal install to refuse here (overridable with a --force flag) 
because reinstalling boot libs (containers, filepath, directory, process, 
time) tends to be a bad idea.

However, xmobar is an executable and no library, so if you unregister the 
packages (from the user db!) after installing before they can cause 
trouble, you should be fine (but no guarantees).