Pressing ^C at the right moment can trash GHC's package list

[igloo]

In  http://www.haskell.org/pipermail/libraries/2007-December/008727.html Peter Gammie says

To my surprise, if you type ^C at the right moment you can trash GHC's
(system-wide) package list.

I'm not sure if this is in ghc-pkg or ghc, but we should check that this can't happen with either program.

[simonmar]

I haven't quite finished working on this yet

[simonmar]

Fixed:

Thu Dec 13 07:40:56 PST 2007  Simon Marlow <simonmar@microsoft.com>
  * FIX #1963: catch Ctrl-C and clean up properlyFri Dec 14 04:33:45 PST 2007  Simon Marlow <simonmar@microsoft.com>
  * always try to remove the new file before restoring the old one (#1963)

On Unix I think this is robust now. On Windows I occasionally get a "permission denied" failure when ghc-pkg tries to restore the old package database after Ctrl-C, but I don't know why this happens, or how to avoid it.

[igloo]

Merged

[duncan]

Instead of the dodgy backing up of the old file, it should use the writeFileAtomic from Cabal. On Unix it is genuinely atomic (assuming ^{C is turned into an exception) and on Windows there is a very narrow race condition but it's probably a good deal narrower than in ghc-pkg's current impl.}

[igloo]

writeFileAtomic sounds like it belongs in base, not Cabal.

[duncan]

Replying to igloo:

writeFileAtomic sounds like it belongs in base, not Cabal.

Yeah it does. See #2298.

[simonmar]

Fixed:

Wed Aug 13 15:37:38 BST 2008  Simon Marlow <marlowsd@gmail.com>
  * FIX #1963: use Cabal's writeFileAtomic to write the new package.conf
  This depends on #2298 also being fixed, which I'll do shortly