Hi,

Don't review or apply this yet. I'm only sending it to the patch
tracker as this seems like a good place to keep work-in-progress
that others might want to look at or take further.

The basic point is to modernise darcs' exception handling away
from the old and deprecated non-extensible exceptions.

To maintain backwarsd compatibility with GHC 6.8, it uses the
extensible-exceptions package. This means that many of the imports
are of Control.Exception.Extensible. Once we drop GHC 6.8, these
imports should be changed to Control.Exception and the
extensible-exceptions dependency dropped.

I haven't tested it properly, or cleaned it up or considered alternative
techniques for converting the code. I have also conducted a fairly
literal conversion where some better cleanups of the existing code
may instead be possible.

Ganesh

Wed Dec 16 01:30:22 GMT 2009  Ganesh Sittampalam <ganesh@earth.li>
  * switch to extensible exceptions

Attachments

• switch-to-extensible-exceptions.dpatch
• unnamed

I've now run the tests on GHC 6.8.3, 6.10.4 and 6.12.1, and also checked the
changes more carefully and concluded that I'm happy to submit the initial
version I sent.

I think the only place where I change semantics is in a few places in
Darcs.Lock, where the code used to catch any kind of exception and now just
catches IO exceptions. Because the handlers are wrapped around an IO operation,
I think this is appropriate - in a couple of places the handler is being used to
annotate the error message with information on what file failed, and in another
place it's being used to trigger a retry. I don't think it makes sense to do
either of these things for non-IO errors.

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