Add Elm.gitignore

[marcelbuesing]

http://elm-lang.org/

[jasonkuhrt]

Please LGTM

[chendrix]

👍

[Apanatshka]

Complete information:

The Elm programming language is on elm-lang.org.
This gitignore ignores build artefacts and downloaded dependencies. The directory name was decided on here.

(copied from my PR, I didn't notice this one)

[bbugh]

Shouldn't this re-include elm-stuff/exact-dependencies.json, like so? If I understand correctly, that file is significant, much like Gemfile.lock.

elm.js
elm-stuff/*
!elm-stuff/exact-dependencies.json

(but I'm relatively new to Elm and could be wrong)

[chendrix]

I think it's a matter of if you're publishing a library or a "final application".

E.g. even the Ruby gitignore tells you

# for a library or gem, you might want to ignore these files since the code is
# intended to run in multiple environments; otherwise, check them in:
# Gemfile.lock
# .ruby-version
# .ruby-gemset

If you're writing a final application you may want to check in exact-dependencies.json, a library? nope.

[bbugh]

That should probably be specified in the .gitignore then, the way the Ruby one does. It's pretty important.

[shiftkey]

Closing in favour of #1610 which has some extra rules around the REPL.