I'm trying to use semantic versioning for one of my NuGet Packages (.NET Core 2).
The version looks like this: 1.0.0-my_fancy_branch.123.
As you can guess, I try to set the branch name and the current BuildId as a prerelease tag.
Unfortunately, dotnet build spews this error:
... is not a valid version string.
But why? The absolutely great documentation of dotnet push / nuget does not list any forbidden characters.
According to the reference on NuGet package versions, NuGet uses Semantic Versioning 2.0.0 starting with NuGet 4.3.0. In earlier versions only a subset of SemVer 2.0.0 is supported, but this may still give a hint where the problem with the specified version is.
In Section 9 (about pre-release versions) it is specified that
Identifiers MUST comprise only ASCII alphanumerics and hyphen
[0-9A-Za-z-].
Hence, I guess that the problems in your case are the underscores in the pre-release version.