Policy for minimum supported GMT versions

[seisman]

With GMT 6.5.0 released, now PyGMT supports three GMT minor versions, 6.3, 6.4 and 6.5, although old GMT versions may have some bugs and miss some features. Supporting multiple GMT versions is a big burden for us maintainers, so we need to decide our policy for the minimum supported GMT versions.

Here are a few options:

1. No policy, i.e., try our best to support the oldest GMT version, unless there is no way or very difficult to be backward-compatible
2. Follow SPEC 0's recommendations for Python versions (Migrate from NEP 029 to SPEC 0 #2863), and support for GMT versions to be dropped 3 years after their initial release.
3. Follow SPEC 0's recommendations for core package dependencies (Migrate from NEP 029 to SPEC 0 #2863), and support for GMT versions to be dropped 2 years after their initial release.

FYI, GMT usually has one release per year (https://github.com/GenericMappingTools/gmt/tags).

• GMT 6.3.0 was released on Nov 19, 2021
• GMT 6.4.0 was released on Jun 16, 2022
• GMT 6.5.0 was released on Jan 7, 2024

[weiji14]

We can probably support about 2-3 minor GMT versions at a time, so maybe go with Option 2 (drop GMT versions after 3 years)? That's assuming that GMT continues to have a minor release every year, which means PyGMT will support at least 2 (or more) GMT minor versions at a time.

[seisman]

I'm also in favor of option 2. Ping @GenericMappingTools/pygmt-maintainers for comments.

[seisman]

Ping @yvonnefroehlich @willschlitzer @michaelgrund for comments. Otherwise, we will go with option 2.

[yvonnefroehlich]

I feel PyGMT should support the last 2-3 GMT versions. From my experience, many users are not updating GMT immediately after a new release. I personally prefer to stay with the same GMT version for a publication, which can easily take a year (or more) to be finally published. So, I think option 2 is a fair compromise between supporting older GMT versions and the work for developers and maintainers.

[seisman]

I think we will go for option 2. Need to document the policy in README, doc/maintenance.md, doc/minversions.rst and also need to update the release checklist. Let's wait for #3056 and #3059 first.