[Discuss][Release][Go] Major Version handling for Go

[Matthew Topol <mt...@factset.com>]

It was suggested that I should advertise this in the dev mailing list as it is a significant change.

When developing Go modules, if you do a major version release you need to update the module import path to add a `v#` suffix in order for the go tooling to handle the version properly. Up until now, since we didn't have the corresponding tags, anyone using the Go library would always get the master branch whenever they downloaded or upgraded their version of the Go module. There was no way to get just version 5 unless you knew the branch name or commit hash. You couldn't just do `go get github.com/apache/arrow/go/arrow@v5`<mailto:github.com/apache/arrow/go/arrow@v5%60>.

In order to fix this, a PR was made to update the release scripts to add the necessary tags, but we also needed to update the module import path. Given the dependencies of the Parquet module on the Arrow module, it made sense to make a change. Previously they were both separate modules with their own go.mod files. In order to ensure they remain in sync when versioning, I pushed https://github.com/apache/arrow/pull/11570 which will lift the go.mod up one directory making them separate packages of a single module rather than two separate modules.

For any users there will be a one time transition they'd need to make in order to upgrade to the newest release in that their own go.mod dependency would now be `github.com/apache/arrow/go` rather than `github.com/apache/arrow/go/arrow` and in order to upgrade to version 6, in their code they would change the import path from `github.com/apache/arrow/go/arrow` to `github.com/apache/arrow/go/v6/arrow`. Their actual code wouldn't have to change beyond the import path changes (except for any breaking changes in new versions).

This also means that every major version release would also require a change like this which touches every one of the .go files and updates the go.mod to the new major version suffix.

For more reference here's a couple links:

  *   https://golang.org/doc/modules/major-version
  *   https://go.dev/blog/v2-go-modules

--Matt