Add conversion from cabal files

[yamadapc]

Adds modules Hpack.Convert and Hpack.Convert.Run for reading a
GenericPackageDescription onto a Package and running the user-facing
conversion routine.

The user-facing option is exposed through:

$ hpack --convert [cabal-file|project-dir]

---

Also adds tests testing we can read cabal files generated from some of
the README examples and hpack's into package.yamls that look like the
original ones.

Everything should be supported, including converting conditionals.

I really need feedback on how to make Hpack.Config Package related
ToJSON instances cleaner. That's the ugly bit of the code.

There some cases where we run into problems in conversion. For example,
the Cabal library does not expose in its data-structures if buildable
was specified or not. To keep the output clean, I initially striped it
from sections if it was true, but then empty conditional blocks could be
generated. Right now it'll only output buildable if it's not
redundant based on context. It'll also remove any empty conditional
branches.

This closes #63.

[yamadapc]

Tests are failing because of a key sorting and an encoding issue. I'll fix later today.

[mgsloan]

Awesome!!

[sol]

If it's me, I would try to avoid this kind of logic here and instead do things like this in a conversion step.

[sol]

Hey, this looks really useful. But it's quite some code and my bandwidth is still limited. @yamadapc would you be willing to maintain this as a separate package?

We would then add prominent references to the README etc., so that discoverability is not an issue.

I think even if I would do it myself, I would at least go for two separate executables (UNIX style).

[yamadapc]

I'm fine with doing that.

I started it and ran into a couple of problems:

• I need to expose HasFieldNames from Hpack.Config
• I need to expose Hpack.GenericsUtil and Hpack.Util

Those are the ones I can solve with a fork/PR, no biggie.

---

And then there's one which I can't understand:

        Couldn't match type ‘Rep SourceRepository’
                       with ‘GHC.Generics.M1 GHC.Generics.D d1 m1’
        The type variables ‘d1’, ‘m1’ are ambiguous
        In the expression: genericToJSON_
        In an equation for ‘toJSON’: toJSON = genericToJSON_
        In the instance declaration for ‘ToJSON SourceRepository’

In all uses of the genericToJSON_ function. I think it has to do with the typeName stuff only working for data types defined in the current module. I'm not familiar with GHC.Generics.

Maybe it's what these guys are talking about..

Ideas?

[soenkehahn]

@yamadapc: Do you have a wip branch where we can take a look at the code producing that Generics type error?

[yamadapc]

@soenkehahn This gives you the error: https://github.com/yamadapc/hpack-convert-separate-package-with-hpack-dependency

But talking with Simon, we had reached the conclusion that it'd be easier to leave hpack-convert on a separate package that'd just fork hpack. I just need to do the laundry on this enhancement/63-convert-cabal-files branch and update the executable/README.

EDIT A gist of the full output https://gist.github.com/9479f0bd3843e81a20ebfbd771614d1d

[soenkehahn]

@yamadapc: I see. Looking forward to this. :)

[yamadapc]

Ok, it has been published on Hackage as hpack-convert and is on my GitHub account as an hpack fork in https://github.com/yamadapc/hpack-convert.

People can choose to:

• Install from source
• Download a binary
• curl -F "cabalfile=@./echo *.cabal" https://hpack-convert.herokuapp.com

I'll keep it on my todo list to make it clean and have it merged back upstream. Even though it's a fork it's not hard to just cherry-pick commits back here at any point.

---

Closing this in favor of this approach.

[sol]

We may still want to add it to the README. PRs welcome!

Sent from mobile

On 9 Aug 2016, at 6:55 PM, Pedro Tacla Yamada [email protected] wrote:

Closed #114.

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[soenkehahn]

@yamadapc: Just tried this out, awesome work!