Extend plugin API to support a list of values

[cr0]

At the moment the plugin API does not support the restriction of possible input values, i.e. a user can enter anything he wants. Basically, supporting enums should fix this problem.

[binwiederhier]

What for? Use case?

[cr0]

We can use that, for instance, at the s3 plugin to let a user choose his storage location. The entered setting isn't validated anywhere at the moment.

[binwiederhier]

That is indeed a use case. However, in particular for this use case, new zones can be added or removed. Frankfurt (eu-central-1) was added very recently. So in this case, we'd need a "suggestion box" -- much like a browser bar.

However, this is so low priority I can't even tell you how low this should be on our list :)

[cr0]

I strongly disagree that this should be a suggestion box because that won't bring any advantages over plain strings.
In your example: If a server is added, we patch the plugin and that's it. What happens if a user makes a typo like eu-centrel-1? With lists we can simply prohibit these kind of errors. However, I see your point that this is really minor.