Migrate to dhall 1.26.1 and merge types and terms

[clementd-fretlink]

The latest dhall version allows to have types and terms in a given record. That allows to use records as proper modules without having separate files for types and terms.

Since all the files are small here, I merged related types and terms. I think it improves clarity (by improving locality)

Things to look at

I've loosely followed the conventions used in Prelude (https://github.com/dhall-lang/dhall-lang/tree/master/Prelude):

• a package.dhall file per dir
• when a module exports both an eponymous type and values, the type is exported under Type

What I did not follow:

• for Addon and Config, the type is defined inline instead of in a separate file. The multiple files containing a single line made navigating our codeconfigbase tedious, so improving locality is a net improvement imo
• all files have a .dhall extension (omitting it would break our tooling or would require brittle config rules)

ToDo

I'd like to test an end-to-end

[cyrilfretlink]

Shouldn’t exports.dhall be named package.dhall to comply with the convention in Dhall prelude?

[clementd-fretlink]

ah great point, I wasn't aware of this convention. I'll make the change

[clementd-fretlink]

(if there are other conventions I'm not following, please tell me)

[paulrbr-fl]

I don't really like files without extensions (it can be confusing for new people coming on the dhall codebase) would you mind keeping all dhall files with the .dhall extension?

[clementd-fretlink]

« je vois que nous en sommes arrivés à la même conclusion, avec cependant un léger avantage pour moi : j'ai remis les .dhall » (extremely OSS117 voice)

[paulrbr-fl]

Looks good, I'll approve but please try to do an end-to-end test before merging :)

[ismaelbouyaf]

That’s a nice change!

[clementd-fretlink]

Yeah, I'm quite happy with it :-)

[paulrbr-fl]

I will happily approve now that an end-to-end test was performed (and succeeded)