PVP proposal: no upper bounds on non-upgradeable packages

[Antoine Latter]

I haven't tested this with the new cabal-install solver, but with the old
one the user would get much worse error messages if 'template-haskell' had
bounds - cabal-install would start trying to install the old version and
fail, sending the user off on a wild goose chase trying to figure out how
to make that install work.

If you have no bounds then the error is much easier to diagnose - the
library needs to be modified to work with the version of template-haskell
currently installed.

I'm +1 on this policy, even though I would prefer the fix be in
cabal-install itself.



On Wed, Apr 9, 2014 at 3:24 PM, Michael Snoyman <michael at snoyman.com> wrote:

> At Herbert's request, I'm splitting off this part of the PVP proposal I
> made[1] to its own separate proposal. Same discussion period of three
> weeks. The proposal is:
>
> Upper bounds should not be included on non-upgradeable packages, such as
> base and template-haskell (are there others?). Alternatively, we should
> establish some accepted upper bound on these packages, e.g. many people
> place base < 5 on their code.
>
> The purpose (elaborated in my blog post[2]) is that these upper bounds
> virtually never provide for a successful build. Instead, they are purely
> about what error messages the user receives. With this change:
>
> * Some build plans that would have previously been impossible are now
> possible, without resorting to the nuclear option of --allow-newers.
> * Instead of cabal version bound error messages, users get GHC compiler
> errors that can be fed back upstream to help get packages fixed more
> expediently.
>
> Downsides I'm aware of:
>
> * If you consider the cabal error messages more user friendly, then the
> error message quality goes down.
> * Users may find out later than they do right now about a failing build.
>
> [1] http://www.haskell.org/pipermail/libraries/2014-April/022529.html
> [2] http://www.yesodweb.com/blog/2014/04/proposal-changes-pvp
>
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