Oddity with 'cabal install' in GHC 7.4.1

[Conal Elliott]

Ah -- so use cabal-dev for development and cabal-install when a version
stabilizes?  -- Conal

On Sun, Feb 5, 2012 at 4:20 PM, Jason Dagit <dagitj at gmail.com> wrote:

> On Sun, Feb 5, 2012 at 10:48 AM, Conal Elliott <conal at conal.net> wrote:
> > On Sun, Feb 5, 2012 at 12:43 AM, Andres Löh <andres.loeh at googlemail.com>
> > wrote:
> >>
> >> Hi Conal.
> >>
> >> > Thanks for the reply! Note that I get this message even running 'cabal
> >> > install' a second time after changing nothing. Is that scenario an
> >> > example
> >> > of what you mean by a "potentially dangerous cabal invocation"?
> >>
> >> The check currently is entirely ad-hoc. Any reinstallation of an
> >> existing package triggers the warning. There's no hash comparison.
> >
> >
> > I'm confused. Isn't package re-installation an extremely common thing in
> > cabal while developing software?
>
> I would say, "You should never mutate your user or global package
> database" and recommend using cabal-dev.  The way cabal-install does
> destructive updates is evil. In particular, it likes to mutate your
> global or user package database.  You run the risk of building
> something and then breaking it later by mutating its dependencies.
>
> With cabal-dev it would be more like this:
> # Suppose you're in the source of bar
> # Further suppose you just changed
> # dependency 'foo' that you're also developing
> cabal-dev add-source ../foo
> cabal-dev install --reinstall foo
>
> Technically this still mutates a package database but, it's a
> throwaway package database in the bar directory.  I lose very little
> when I 'rm -rf cabal-dev dist' and my user and global package
> databases stay in tact.  I feel as though I can't sing the
> sandboxed-build praise loudly enough.  The time my computer takes to
> rebuild packages is negligible to the human time spent dealing with
> broken package databases..
>
> I hope that helps,
> Jason
>
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