On Sat, Feb 4, 2012 at 9:51 PM, Andres Löh wrote:

Hi Conal.

On Sun, Feb 5, 2012 at 12:36 AM, Conal Elliott 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

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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 wrote:

Hi Conal.

On Sun, Feb 5, 2012 at 12:36 AM, Conal Elliott 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

...

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

On Sun, Feb 5, 2012 at 10:48 AM, Conal Elliott wrote:

On Sun, Feb 5, 2012 at 12:43 AM, Andres Löh 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