[darcs-users] GHC 6.10 compatibility patches

David Roundy droundy at darcs.net
Fri Oct 17 16:50:37 UTC 2008

On Fri, Oct 17, 2008 at 09:28:48AM -0700, J. Garrett Morris wrote:
> Hello everyone,
> In the process of testing the franchise build on Vista, I discovered
> that GHC 6.10 complains about several warnings which stop the build
> process because of -Werror.  They are: -fffi is deprecated, and unused
> imports.  I've attached a patch which resolves these issues.  I don't
> know when -XForeignFunctionInterface was introduced though, or how to
> make the GHC flags dependent on GHC version, so this might be the
> wrong idea.

Note that you can run

./setup.hs configure --disable-Werror

to compile in spite of warnings.  But I appreciate that you didn't do
this (since we do want to fix the warnings)!

Your first patch for the -fffis looks fine and compiles here on ghc
6.8.2.  We'll see when the tests run on ghc 6.6 whether
-XForeignFunctionInterface is sufficiently portable.  Otherwise we'll
have to figure out something tricky, probably specifying -fffi in the
setup.hs file, which would mean that all files would be compiled with
-fffi.  I don't see how this would hurt, but it seems a bit wrong.

The second patch, however, removing the import of system from
src/Exec.lhs seems very, very odd.  It certainly causes the compile to
fail for me, and I don't see how it could work for you with this
patch, since system is definitely used in this file.  Do you have an
explanation for this? Does it really compile for you with the patch
you sent?

The obvious answer would be that the difference involves #ifdefs that
differ between your machine and mine, but so far as I can see the
system is used in Windows in the definition of exec_interactive at
line 141.  My only guess is that ghc 6.10 is doing something seriously
weird to cause this not to call System.Cmd.system, but I don't have a
good guess as to what that weird behavior might be.

> I hope I got the patches attached correctly - this is my first shot at this.

The patch looks great (apart from the above trouble with the import
removal patch), thanks! I've applied the first one, but it'll be a
little while before we see if it passes tests on ghc 6.6 and the push
to the central repository succeeds.


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