Use version from annotated tag

[mockitoguy]

There are teams that prefer to cut release "on demand", rather than with every change on master (example: linkedin/li-apache-kafka-clients, mockito-kotlin). Those teams are not supported cleanly by our plugin.

Problem statement: how do we enable teams to release on demand and provide automated changelog?

❓ Options

• a) keep shipkit-auto-version simple, let other plugins solve this use case. Problem: allegro/axion-release-plugin does not expose previous version information cleanly and it is necessary for automated changelog.
• b) enhance shipkit-auto-version to support picking the version directly from annotated tag.

💡Solution discussion:

• a) is preferred to keep shipkit-auto-version laser focused and reduce future maintenance. However, I was not able to cleanly enhance axion plugin to expose previous version information.
• b) can be designed as a simple enhancement to shipkit-auto-version ⬇️

🌱 Implementation overview:

• missing version.properties file or missing version property is allowed and signals simplified behavior of our plugin (currently, the file and property are required).
• our plugin deducts current version this way:
  • if we checked out a tag (git checkout 1.2.3), pick that version: 1.2.3
    • To find out if git repo is checked out to a tag, we can run git describe --tags
  • if we checkout out a branch (git checkout main), pick the highest tag
  • no counting commits logic is necessary in this simplified behavior

🌎 Long term goals:

• should we deprecate functionality ⬆️ when axion plugin supports previous version information? No. Shipkit-auto-version will continue to support the basic use case described in this ticket. We endorse axion plugin for complex use cases not supported out of the box by shipkit-auto-version. However, we encourage build experts to keep their automation simple (KISS 💋).

[mockitoguy]

@shestee, do you want to take a stab at it?

[shestee]

Thank you for asking. I'll check this out.

[nipafx]

Just a note:

• missing version.properties file or missing version property is allowed and signals simplified behavior of our plugin

When I experimented with #72 I explored passing the project version via command line, which also makes version.properties superfluous, I discovered that the file is required nonetheless. This seems to contradict the docs, which say:

• if the gradle project already has a set version (e.g. from the command line), use that version
• if no file or wrong format fail

[mockitoguy]

@nipafx, I clarified that in the description (we're changing this behavior). Thx!