Backporting srcLoc to the GHC 7.10 branch

Eric Seidel eric at
Mon Mar 23 18:14:16 UTC 2015

IIRC the patch doesn't directly depend on -fwarn-redundant-constraints,
but I think I ran into some merge conflicts that had to be resolved. I
agree with Austin that backporting it should be doable, and would be
happy to help if there's interest.

Also, I still mean to submit a follow-on patch that uses the new srcLoc
infrastructure to add locations to explicitly-failing functions (i.e.
error, undefined, and maybe assert). I don't know if this will be
palatable to GHC-HQ as it changes base, but I think it's at least a
discussion worth having. Unfortunately I got sidetracked by school stuff
and haven't had a chance to throw the patch together yet..

On Mon, Mar 23, 2015, at 10:50, Austin Seipp wrote:
> Hi Michael,
> I actually tried to adopt this patch into 7.10, because I thought it
> was needed for another dependent patch we wanted. Unfortunately, the
> backtrace-via-implicit-params patch seems to depend on some prior work
> by Simon PJ in the typechecker (-fwarn-redundant-constraints, a rather
> large patch), which we *did not* want in 7.10 (the *textual* diff
> applied fine, but there were some API changes the backtrace patch
> needed, so it failed to build). So, in the end, it was easier to
> surgically remove this patch from the one that depended on it, and it
> had a much lower 'surface area' of changes, than adopting both. Hope
> that makes sense.
> Also, as Simon said, we don't normally do big changes like this in
> point releases, so I think this is unlikely to happen.
> So the short story is "afraid not". But a backport should be possible,
> if you're willing to get your hands a bit dirty (any conflict will
> likely be fairly easy to fix, but it will involve some textual
> munging).
> On Mon, Mar 23, 2015 at 6:49 AM, Michael Snoyman <michael at>
> wrote:
> > It looks like the srcLoc change[1] is something that some of our (FP
> > Complete's) customers would be quite interested in getting access to sooner
> > rather than later. Would there be any possibility of getting that patch
> > merged into the 7.10 branch of GHC? I'm not sure if I'd try my luck at
> > actually including it in 7.10.1, but would it be on the table for 7.10.2?
> >
> > We do of course have the option of backporting it ourselves and including it
> > in a custom GHC we provide customers, but we generally try to stay as close
> > to upstream as possible.
> >
> > [1]
> >
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> >
> >
> -- 
> Regards,
> Austin Seipp, Haskell Consultant
> Well-Typed LLP,
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