Add Elm Section

[ajlende]

Thanks for you pull-request!

Please, make sure you've read CONTRIBUTING.md before submitting this PR.

Description

This adds support for Elm since #253 hasn't been touched in almost a year. I'm making a companion section for getting information for individual projects in #527.

I added some tests as well, but this is my first time doing tests for shell scripts, so let me know if I've done those correctly.

Screenshot

Please, attach a screenshot, if possible.

[salmanulfarzy]

This is one of the comprehensive feature PR I've seen in this repo, awesome @ajlende 👏

What do you think about this,

Also, is the Elm version changes so often that it needs to be shown in prompt? Would it be useful for users and make the clutter in prompt? Is there any Elm version management systems, like nvm for Node.js?

From #253 (comment)

[ajlende]

Is there any Elm version management systems, like nvm for Node.js?

No, I've been handling needing multiple versions by having differently named binaries. Similar to how Python has python3 vs python, I have elm vs elm18. That was my personal solution to working with both versions. As far as I know, there isn't an official recommended way to handle multiple versions of Elm.

Is the Elm version changes so often that it needs to be shown in prompt?

Historically, a new version of Elm has been released every 6-9 months. However, Elm still hasn't hit the first stable version, so each has had pretty significant backwards-incompatible changes.

Would it be useful for users and make the clutter in prompt?

I originally had this built into #527 (elm_project) because it seemed a little strange to me to show the project's needed Elm version without the installed Elm version. But after seeing #253 and because the configuration was getting out of hand, I decided to break this out into a separate thing. I can merge this back with elm_project if you think it fits better bundled as one.

@salmanulfarzy Thanks for scrutinizing new features to this. To me, that means I'll be able to keep using spaceship-prompt knowing that it's not going to get bloated with useless features.

[salmanulfarzy]

Some minor suggestion about code formatting and tests

[salmanulfarzy]

Just noted the following from #527 (comment)

is the Elm version changes so often that it needs to be shown in prompt? Would it be useful for users and make the clutter in prompt?

Recently, Elm updated to 0.19.0, so I (and I'd expect many others) still have quite a few 0.18.0 projects and some 0.17.0 (or earlier) projects. Elm doesn't have an equivalent to nvm, so I've personally handled the different versions by just having differently named binaries. This would allow me to see at a glance which elm binary I need to run for a particular project.

This does look like good use case to display version information.

I can merge this back with elm_project if you think it fits better bundled as one.

I think they are better as separate sections. @denysdovhan prefers each section as atomic as possible -- #340 (comment)

[salmanulfarzy]

LGTM. Merging this as previously approved

[salmanulfarzy]

Thank you for contributing @ajlende 🎉