Expose the prelease part of SemVerPadded

[sunsided]

For dnx/dnu-based builds (#647), I'm required to set the DNX_BUILD_VERSION environment, which will replace the placeholder asterisk in project.json. An DNX_BUILD_VERSION=unstable1234 with a 1.0.0-* setting would result in a 1.0.0-unstable1234 build and NuGet package.

In order to circle around incompatibilites with dnx-based, GitVersion and v2-based NuGet feeds, the prerelease and padded prerelease part (e.g. unstableXXXX of LegacySemVerPadded) is required as a separate export.

Alternatively a GitVersion.DnxBuildVersion could be exposed.

[sunsided]

For the record, I worked around this at the moment using a powershell script in TeamCity to split the version number and then pad it manually. The script can be found in this gist.

[JakeGinnivan]

I am struggling to find where DNX_BUILD_VERSION and such is documented. Does it automatically remove the - for you if no build version is specified?

[asbjornu]

Woudn't GitVersion.DnxBuildVersion be the cleanest and most consistent way to expose this?

[sunsided]

@JakeGinnivan there's probably no point searching for any documentation at the moment, it's still in the process of being written for very large parts. But yes, indeed, it's as you suspect. Have a look at my comments on #647.
@asbjornu I personally dislike this option as it implies the usage. As such, it might underly some constraints the user's not aware of if he requires the same information elsewhere. If the tag part of the nuget version is all he needs, why not use that. That said, I'm fine with either option.

[JakeGinnivan]

I am leaning towards @sunsided's idea, I wasn't a massive fan of NuGetVersion because GitVersion was supposed to be agnostic but it did make it more discoverable. For DNX I'm not so sure as it is far more lightweight and hopefully doesn't have all the issues NuGet has.

We should just expose BuildNumber which is normally commit count, and also expose BuildNumberPadded. I also think we should have PreReleaseDash or something for doing manual concatenation rather than PreReleaseTagWithDash

[asbjornu]

@JakeGinnivan Sounds good! 👍

[JakeGinnivan]

I think this is covered by existing variables plus #742

Am I missing anything?