Using a development snapshot of happy

[Moritz Angermann]

This dependency on alex and happy to boot ghc has been annoying, but
wasn't  that terrible until a while ago when some
ghc versions needed happy <= 1.19.11 and others happy >= 1.19.12. If
happy was part of ghc, this would not have been an issue.
As such I'd be on board with adding happy *and* alex as submodules
into the `utils` folder. And thereby reducing the external
boot dependencies of ghc!

I believe
- `compiler/ghc.cabal.in` would need to get a `build-tool-depends:`
stanza for happy and alex,
- `utils/genprimopcode/genprimopcode.cabal` same
- `utils/hpc/hpc-bin.cabal` same for happy only.
For `hadrian`, you'd need to make it aware of happy and alex packages
in `hadrian/src/Packages.hs`.
(Just follow other "util"s in there, e.g. unlit or touchy).

In general hadrian should follow cabal dependencies properly.

cheers,
 Moritz

On Sun, Aug 2, 2020 at 3:43 PM Vladislav Zavialov <vladislav at serokell.io> wrote:
>
> Hi ghc-devs,
>
> I’m working on the unification of parsers for terms and types, and one of the things I’d really like to make use of is a feature I implemented in ‘happy’ in October 2019 (9 months ago):
>
>   https://github.com/simonmar/happy/pull/153
>
> It’s been merged upstream, but there has been no release of ‘happy’, despite repeated requests:
>
>   1. I asked for a release in December: https://github.com/simonmar/happy/issues/164
>   2. Ben asked for a release a month ago: https://github.com/simonmar/happy/issues/168
>
> I see two solutions here:
>
>   a) Find a co-maintainer for ‘happy’ who could make releases more frequently (I understand the current maintainers probably don’t have the time to do it).
>   b) Use a development snapshot of ‘happy’ in GHC
>
> Maybe we need to do both, but one reason I’d like to see (b) in particular happen is that I can imagine introducing more features to ‘happy’ for use in GHC, and it’d be nice not to wait for a release every time. For instance, there are some changes I’d like to make to happy/alex in order to implement #17750
>
> So here are two questions I have:
>
>   1. Are there any objections to this idea?
>   2. If not, could someone more familiar with the build process guide me as to how this should be implemented? Do I add ‘happy’ as a submodule and change something in the ./configure script, or is there more to it? Do I need to modify make/hadrian, and if so, then how?
>
> Thanks,
> - Vlad
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