Oddity with 'cabal install' in GHC 7.4.1

[Conal Elliott]

Since upgrading to 7.4.1, if I 'cabal install' successfully and then 'cabal install' a second time without first doing a 'ghc-pkg unregister <package-name>', I get the following complaint:

cabal: The install plan contains reinstalls which can break your GHC
installation. You can try --solver=modular for the new modular solver that
chooses such reinstalls less often and also offers the --avoid-reinstalls
option. You can also ghc-pkg unregister the affected packages and run ghc-pkg
check to see the effect on reverse dependencies. If you know what you are
doing you can use the --force-reinstalls option to override this reinstall
check.

The only path I've found so far that's willing to rebuild or even say nothing needs rebuilding (when nothing does) is to 'ghc-pkg unregister' and then 'cabal install' again. I'm getting the same behavior on Red Hat 5 and Mac OS 10.6.8, both compiled from sources.

Does anyone know what's going on here?

-- Conal

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[Andres Löh-2]

Hi Conal.

On Sun, Feb 5, 2012 at 12:36 AM, Conal Elliott <[hidden email]> wrote:
> Since upgrading to 7.4.1, if I 'cabal install' successfully and then 'cabal
> install' a second time without first doing a 'ghc-pkg unregister
> <package-name>', I get the following complaint:
>
> [...]

The warning is intended to prevent you from breaking your system
without knowing that you know that you're running a potentially
dangerous cabal invocation.

The --force-reinstalls flag should always make it build. If it
doesn't, it's a bug.

In addition, I'm planning to make the warning a little bit less
aggressive before the release.

> The only path I've found so far that's willing to rebuild or even say
> nothing needs rebuilding (when nothing does) is to 'ghc-pkg unregister' and
> then 'cabal install' again. I'm getting the same behavior on Red Hat 5 and
> Mac OS 10.6.8, both compiled from sources.

I'd be surprised if the OS matters. But as I said, I've not yet
encountered a situation where it wouldn't build given
--force-reinstalls.

Cheers,
  Andres

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[Thomas DuBuisson]

On Sat, Feb 4, 2012 at 9:51 PM, Andres Löh <[hidden email]> wrote:

> Hi Conal.
>
> On Sun, Feb 5, 2012 at 12:36 AM, Conal Elliott <[hidden email]> wrote:
>> Since upgrading to 7.4.1, if I 'cabal install' successfully and then 'cabal
>> install' a second time without first doing a 'ghc-pkg unregister
>> <package-name>', I get the following complaint:
>>
>> [...]
>
> The warning is intended to prevent you from breaking your system
> without knowing that you know that you're running a potentially
> dangerous cabal invocation.
>
> The --force-reinstalls flag should always make it build. If it
> doesn't, it's a bug.
>
> In addition, I'm planning to make the warning a little bit less
> aggressive before the release.

Before the release of what? (seeing as GHC 7.4.1 has been released)

>
>> The only path I've found so far that's willing to rebuild or even say
>> nothing needs rebuilding (when nothing does) is to 'ghc-pkg unregister' and
>> then 'cabal install' again. I'm getting the same behavior on Red Hat 5 and
>> Mac OS 10.6.8, both compiled from sources.
>
> I'd be surprised if the OS matters. But as I said, I've not yet
> encountered a situation where it wouldn't build given
> --force-reinstalls.
>
> Cheers,
>  Andres
>
> _______________________________________________
> Libraries mailing list
> [hidden email]
> http://www.haskell.org/mailman/listinfo/libraries

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[Andres Löh-2]

>> In addition, I'm planning to make the warning a little bit less
>> aggressive before the release.
>
> Before the release of what? (seeing as GHC 7.4.1 has been released)

Sorry, I should have been clear. Before the release of cabal-install.
The described behaviour only occurs in the current development version
of cabal-install. It isn't tied directly to GHC 7.4.1.

Cheers,
  Andres

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[Conal Elliott]

Hi Andres,

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"? I've been unable to avoid this error message by any other means that (a) 'ghc-pkg unregister <package>' or (b) '--force-reinstall'. So far, '--solver=modular' hasn't helped. So I'm hoping for something less aggressive. In particular, in case nothing has changed, I want 'cabal install' to succeed (exit code 0) so that my automated build & install & release processes will continue rather than get stopped.

Regards, - Conal

On Sat, Feb 4, 2012 at 9:51 PM, Andres Löh <[hidden email]> wrote:

Hi Conal.

On Sun, Feb 5, 2012 at 12:36 AM, Conal Elliott <[hidden email]> wrote:
> Since upgrading to 7.4.1, if I 'cabal install' successfully and then 'cabal
> install' a second time without first doing a 'ghc-pkg unregister
> <package-name>', I get the following complaint:
>

> [...]

The warning is intended to prevent you from breaking your system
without knowing that you know that you're running a potentially
dangerous cabal invocation.

The --force-reinstalls flag should always make it build. If it
doesn't, it's a bug.

In addition, I'm planning to make the warning a little bit less
aggressive before the release.

> The only path I've found so far that's willing to rebuild or even say
> nothing needs rebuilding (when nothing does) is to 'ghc-pkg unregister' and
> then 'cabal install' again. I'm getting the same behavior on Red Hat 5 and
> Mac OS 10.6.8, both compiled from sources.

I'd be surprised if the OS matters. But as I said, I've not yet
encountered a situation where it wouldn't build given
--force-reinstalls.

Cheers,
 Andres

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[Andres Löh-2]

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've been
> unable to avoid this error message by any other means that (a) 'ghc-pkg
> unregister <package>' or (b) '--force-reinstall'. So far, '--solver=modular'
> hasn't helped. So I'm hoping for something less aggressive. In particular,
> in case nothing has changed, I want 'cabal install' to succeed (exit code 0)
> so that my automated build & install & release processes will continue
> rather than get stopped.

The message appears, but building should work, with --force-reinstall
and no --dry-run. Can you confirm that you've tried that?

Cheers,
  Andres

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[Andres Löh-2]

>> I've been
>> unable to avoid this error message by any other means that (a) 'ghc-pkg
>> unregister <package>' or (b) '--force-reinstall'. So far, '--solver=modular'
>> hasn't helped. So I'm hoping for something less aggressive. In particular,
>> in case nothing has changed, I want 'cabal install' to succeed (exit code 0)
>> so that my automated build & install & release processes will continue
>> rather than get stopped.
>
> The message appears, but building should work, with --force-reinstall
> and no --dry-run. Can you confirm that you've tried that?

Actually, the message should not even appear if --force-reinstalls is
given. Are you using the latest development version of cabal-install
from darcs?

Cheers,
  Andres

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[Conal Elliott]

On Sun, Feb 5, 2012 at 12:43 AM, Andres Löh <[hidden email]> 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? Do you cope by habitually adding --force-reinstall during development? Perhaps that habit is the piece missing from my mental picture.

> I've been
> unable to avoid this error message by any other means that (a) 'ghc-pkg
> unregister <package>' or (b) '--force-reinstall'. So far, '--solver=modular'
> hasn't helped. So I'm hoping for something less aggressive. In particular,
> in case nothing has changed, I want 'cabal install' to succeed (exit code 0)
> so that my automated build & install & release processes will continue
> rather than get stopped.

The message appears, but building should work, with --force-reinstall
and no --dry-run. Can you confirm that you've tried that?

Cheers,
 Andres

Yes, building does work for me with --force-reinstall.

-- Conal

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[Jason Dagit-3]

On Sun, Feb 5, 2012 at 10:48 AM, Conal Elliott <[hidden email]> wrote:

> On Sun, Feb 5, 2012 at 12:43 AM, Andres Löh <[hidden email]>
> 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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[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 <[hidden email]> wrote:

On Sun, Feb 5, 2012 at 10:48 AM, Conal Elliott <[hidden email]> wrote:
> On Sun, Feb 5, 2012 at 12:43 AM, Andres Löh <[hidden email]>
> 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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