[Haskell-cafe] uninstalling libraries

[Evan Laforge]

On Sun, Nov 12, 2017 at 8:14 PM, Brandon Allbery <allbery.b at gmail.com> wrote:
> This is something of a nasty problem, considering that storing uninstall
> information separately is not particularly robust. Perhaps ghc-pkg should,
> if it doesn't already, support extension fields that e.g. cabal can use to
> store uninstall information. (But even that potentially has problems, given
> that people are known to copy package registration information between
> package databases. If there is uninstall information in there, what happens
> if someone uninstalls via one or the other copy?)

Aren't packages only allowed to install a restricted set of things
into a restricted set of places?  We have the code (.hi, .a, .so,
etc., in import-dirs / library-dirs), possibly library-specific data
(I assume that's data-dir), and haddock (haddock-html and
haddock-interfaces, awkwardly in separate places).

One problem is that I don't fully understand what those fields mean,
is there documentation somewhere?  And then the fact that these are
all plural so presumably you could have a lot of them, what is that
for?

I'm guessing library-dirs means something like "put this on your -L
line" so it's clearly a mistake to interpret that as "here's where I
put the library", and you'll have things like /usr/local/lib if you
need to link external libraries.

Is there any more complicated install plan than put *.a, *.so, *.hi in
$root/lib/$ghc/$package-$id, put haddock in
$root/share/doc/$ghc/$package, put ad-hoc junk in
$root/share/$ghc/$package?  I assume there must be, but who's doing
that and why?  If it's OS packages, then they have their own uninstall
mechanisms, presumably not ghc's problem.