Add --version flag

[jimafisk]

It would be great if users could see which version of plenti they are using: plenti --version

Currently releases are created automatically based on the git tag used, it would be ideal if the cmd could autodiscover that tag and use it. I would like to avoid having to manually increment versions every deploy because I'm likely to forget.

Potentially use https://github.com/christopherhein/go-version

[jimafisk]

Discussion on automatically updating git tag versions: https://www.reddit.com/r/golang/comments/4cpi2y/question_where_to_keep_the_version_number_of_a_go/

Since we're already using go generate that seems like an approachable way to accomplish this. This article describes the steps:

1. Tag your git repository with a version number (ideally based on the semantic versioning specification e.g. v0.0.0): git tag -a v0.0.0 -m "First tag."
2. Push the version number to the remote repository: git push --tags
3. Generate an up-to-date version_PLATFORM.go file (normally done by your CI server): go generate (The version_PLATFORM.go file gets automatically updated with data from the tag)
4. Build as normal: go build

[jimafisk]

Looks like the example repo from the article above now recommends using ldflags instead: https://www.atatus.com/blog/golang-auto-build-versioning/

[jimafisk]

When enabling "Run" on the rootCmd I was having trouble optionally printing the default info if no --version flag was passed. I could have set up a separate command for "version" (run like plenti version) but I thought this worked better as a flag (run like plenti --version or plenti -v). This post shows you can simply print the default using cmd.Help(). That allows you to continue running plenti to find basic information about the project and how to use it.

[jimafisk]

Helpful article from DO: https://www.digitalocean.com/community/tutorials/using-ldflags-to-set-version-information-for-go-applications

Locally I can set values available in rootCmd like so: go install -ldflags="-X 'plenti/cmd.Version=test'"

[jimafisk]

Needed to fix the build command to use following format:

go install -ldflags="-X 'plenti/cmd.Version=$(git describe --tags)'"

[jimafisk]

It seems .goreleaser.yml is reading the -ldflags as a string, so running plenti -v just prints "git describe --tags" and not the evaluated output of that expression (e.g. v0.2.31). I also tried using backtics but had the same result:

go install -ldflags="-X 'plenti/cmd.Version=`git describe --tags`'"

[jimafisk]

Looks like we can use a Name Template for this: https://goreleaser.com/customization/templates/

Something like -X main.version={{.Tag}} should work.