#2491: ghc-pkg unregister should complain about breaking dependent packages
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Reporter: duncan | Owner:
Type: feature request | Status: new
Priority: normal | Component: Compiler
Version: 6.8.3 | Severity: normal
Keywords: | Testcase:
Architecture: Unknown | Os: Unknown
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Currently it is easy to silently break installed packages. This is
particularly bad when users unregister things like 'old' versions of Cabal
or bytestring (usually after having installed a new version) because this
breaks packages like the ghc api package which cannot be re-installed.
So ghc-pkg unregister should report an error if there are packages that
depend on the package being unregistered (at least within the same package
db). The error message should report which packages still need the package
that the user was trying to unregister and should mention that if they're
really really sure that they want to break other said packages that they
can run the command again with `--force`. With `--force` inplace it should
probably still print the warning (for the benefit of log files in
packaging systems that may need to use `--force` if they do not guarantee
an order of unregistering).
Example user interaction:
{{{
$ ghc-pkg unregister bytestring-0.9.0.1
ghc-pkg: bytestring-0.9.0.1 should not be unregistered
because the following registered packages depend on it:
ghc-6.8.2.
Use --force to unregister anyway and break these packages.
You can use ghc-pkg check at any time to see what packages
in the broken state due to missing dependencies.
$ ghc-pkg unregister bytestring-0.9.0.1 --force
ghc-pkg: Warning: due to the forced unregistering of the
package bytestring-0.9.0.1, the following packages are now
in the broken state:
ghc-6.8.2
}}}
Incidentally, we should also install a package.conf.shipped to help people
recover their ghc installations after they've unwisely and over-zealously
gone round unregistering 'old' packages. Debian and Gentoo already do this
and it's saved many users.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2491>
GHC <http://www.haskell.org/ghc/>
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