[Haskell-cafe] writing a good Setup.hs is *hard* (was: broken on install encoding 0.6.6)

[Antoine Latter]

Ccing cabal-dev.

On Aug 17, 2011 9:12 AM, "Rogan Creswick" <creswick at gmail.com> wrote:
>
> On Wed, Aug 17, 2011 at 6:29 AM, Gang <yugang.bj at gmail.com> wrote:
> >
> > sorry to bother
> >
>
> Not in the least!
>
> I was trying to figure out what problem you were encountering, and I
> learned a lot.  I never did recreate your problem, but in the process
> I ran into a whole host of other annoyances and strange situations
> relating to slightly broken cabal files and cabal build intricacies
> that confound our existing tools.
>
> I don't mean to pick on encoding or HaXml - I've seen the same kinds
> of issues in many, many Haskell packages (including most of the
> packages I've written myself) these are just the ones I ran into
> today. (and I am quite serious when I say that writing a good Setup.hs
> is very, very, difficult).  My objective is just to motivate a minor
> change to cabal that would help to make this easier.
>
> On to the build problems:
>
> encoding-0.6.6 uses it's own source during the build process! It
> actually has to be partially compiled before the build tool can build
> encoding (!).  I'm *amazed* that this actually works at all
> (impressed, too), and indeed, it doesn't work with cabal-dev, which is
> unfortunate: cabal-dev would have identified one of the dependency
> issues in HaXml 1.19 (pretty is an undocumented dependency, although I
> am unsure if that was true at the time 1.19 and encoding-0.6.6 were
> released.  I haven't tracked the pretty dependency down to the exact
> source - it could be a transitive dep introduced by a recent version
> of something HaXml 1.19 needs.  Per my subject line - this is
> amazingly difficult - keep in mind that we're not talking about
> building *packages*, this is just to build the *build tool*, and none
> of this is documented.  How long before it is effectively impossible
> to recreate the circumstances that result in a successful
> encoding-0.6.6 build?).
>
> cabal-dev can't build encoding-0.6.6 because the encoding source that
> is referenced from encoding's Setup.hs depends on (at least) HaXml >=
> 1.19 && < 1.22.5; this is OK with cabal, since cabal-install installs
> a necessary HaXml into your user package db prior to building
> encoding's Setup.hs (modulo the missing upper version bound).
> Therefore HaXml "just happens" to be visible when cabal builds
> Setup.hs -- a build step that cabal-dev isn't capable of controlling
> (and probably never will be -- we could intercept system calls, but
> that's difficult when only supporting one OS, much less three).
>
> You can, of course, manually install HaXml to your local package db
> and then cabal-dev install encodings, but that's somewhat of a hack
> (and you'll find that the current HaXml won't work for the current
> encodings release, as Gang Yu did).
>
> Adding a section to the cabal file that specifies build dependencies
> for Setup.hs would make some very important parts of this process
> obvious - and it would *greatly* assist in debugging failing builds,
> not to mention allowing us to make use of the extensive libraries on
> hackage to write more expressive build systems.  (We could actually
> use openshake in Setup.hs, once it's released, for example!)
>
> I've floated the idea past a number of Haskell programmers with
> positive responses, and there is a GSOC ticket that provides some more
> details (the project was not selected - no students proposed to work
> on it):
>
> http://hackage.haskell.org/trac/summer-of-code/ticket/1602
>
> --Rogan
>
> > Regards
> > Gang
> > On 08/17/2011 04:59 PM, Gang Yu wrote:
> >
> > hi, cafe:
> >
> >     I go through to the encoding package installation problem again.
> >
> >  cabal install encoding
> > Resolving dependencies...
> > /tmp/encoding-0.6.68093/encoding-0.6.6/dist/setup/setup: 4: Syntax
error:
> > ";" unexpected
> >
> > when I have a check on the this issue, I get:
> >
> > file
> > ~/.cabal/packages/
hackage.haskell.org/encoding/0.6.6/encoding-0.6.6/dist/setup/setup
> > /home/gang/.cabal/packages/
hackage.haskell.org/encoding/0.6.6/encoding-0.6.6/dist/setup/setup:
> > ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked
> > (uses shared libs), for GNU/Linux 2.6.27, not stripped
> >
> > My machine is:
> >
> > gang at gang-laptop:~$ uname -a
> > Linux gang-laptop 2.6.38-8-generic #42-Ubuntu SMP Mon Apr 11 03:31:50
UTC
> > 2011 i686 i686 i386 GNU/Linux
> >
> > is this related? How can I manually install the package from scratch?
Any
> > helps or directs will be appreciated
> >
> > Thanks
> > Gang
> >
> >
> > _______________________________________________
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> >
> >
>
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