[Haskell-cafe] Version constraints and cabal.config files

[Michael Snoyman]

On Wed, Mar 25, 2015 at 7:35 PM Anthony Cowley <acowley at gmail.com> wrote:

>
>
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> On Mar 25, 2015, at 11:03 AM, Michael Snoyman <michael at snoyman.com> wrote:
>
>
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> On Wed, Mar 25, 2015 at 4:58 PM Anthony Cowley <acowley at gmail.com> wrote:
>
>>
>>
>> On Mar 25, 2015, at 10:51 AM, Michael Snoyman <michael at snoyman.com>
>> wrote:
>>
>>
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>> On Wed, Mar 25, 2015 at 4:30 PM Anthony Cowley <acowley at seas.upenn.edu>
>> wrote:
>>
>>> On Wed, Mar 25, 2015 at 10:24 AM, Michael Snoyman <michael at snoyman.com>
>>> wrote:
>>> >
>>> >
>>> > On Wed, Mar 25, 2015 at 4:17 PM Anthony Cowley <acowley at seas.upenn.edu
>>> >
>>> > wrote:
>>> >>
>>> >> The suggestion to use "cabal install --dependencies-only ..." instead
>>> >> of "cabal freeze" in that issue is really nicely presented. "cabal
>>> >> freeze" is close to the right thing, but it's just not as fully
>>> >> featured as "cabal install" (e.g. taking flags).
>>> >>
>>> >> As for Stackage, I think it would be helpful to cache the full build
>>> >> plans computed for each package in Stackage. This is most of the work
>>> >> my Nix tooling currently does, so it would be a big time saver.
>>> >>
>>> >>
>>> >
>>> > By "full build plans," do you mean the dist/setup-config file, or
>>> something
>>> > else? That file would be problematic since it's Cabal-library-version
>>> > specific IIRC. If you're looking for the full listing of deep
>>> dependencies
>>> > and versions, we can extract that from the .yaml file using the
>>> technique I
>>> > mentioned earlier.
>>> >
>>> > Michael
>>>
>>> Yes, I meant the full listing of deep dependencies.
>>>
>>>
>>>
>> I've put together a Gist with an executable that does what I described:
>>
>> https://gist.github.com/snoyberg/5b244331533fcb614523
>>
>> You give it three arguments on the command line:
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>> * LTS version, e.g. 1.14
>> * Name of package being checked
>> * true == only include dependencies of the library and executable,
>> anything else == include test and benchmark dependencies as well
>>
>> If that's useful, I can package that up and put it on Hackage.
>>
>> Michael
>>
>>
>> This is very helpfulness, thanks! There is a bootstrapping issue, though,
>> which is, I imagine, why both Miëtek and I have been writing much more bash
>> than we'd like. But perhaps this becomes part of a cabal-install-like
>> bootstrap.sh script to get things going.
>>
>> Anthony
>>
>
> Oh, that's actually a great idea. What if we had a program that:
>
> 1. takes a set of packages that needs to be installed, and an LTS version
> 2. computes the dependency tree
> 3. writes out a shell script (possibly batch program?) to wget, tar xf,
> and runghc Setup.hs in the correct order to get all of those packages
> installed
>
> As you can tell from the program I just threw together, stackage-types
> supports this kind of thing pretty trivially.
>
> Michael
>
>
> Yes, that's what the Nix tooling does. The extra bits are building up
> package databases suitable for each build without copying files all over
> the place. That has the extra benefit of being able to reuse builds when
> the recipe is unchanged. It is definitely not hard, but getting the build
> plans from stackage in a portable way would be valuable.
>
> Anthony
>

OK, I've updated the Gist so that it produces a shell script that will
install all necessary packages. It also has a nicer optparse-applicative
interface now.

https://gist.github.com/snoyberg/5b244331533fcb614523

One thing I didn't do here is add support for custom GHC package databases.
I assume you'll need that, but wasn't sure exactly how you're doing that in
Nix.

If this is useful for you, I'll start a stackage-bootstrap repo, clean up
this code a bit, and we can continue improving it from there.

Michael
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