Raise the minimum supported version of Gradle to 4.10

[wilkinsona]

In 2.1, we raised the minimum supported version of Gradle to 4.4. We should raise it again in 2.2. We currently test against 12 different versions (seven 4.x versions and five 5.x versions) which is broader than I would like. I think it may be too aggressive to drop support for 4.x completely in 2.2, but we should be able to drop some older 4.x releases. We should even consider deprecating 4.x support in 2.2 with a view to dropping it in 2.3. This would clear the way a little for supporting Gradle 6 without being hampered by trying to support 3 different major versions at the same time.

@eriwen @jlstrater do you have any data points that you are happy to share that would help to guide us here? The move to 4.4 as a minimum in 2.1, that was based on your advice, seemed to go almost unnoticed. Anything you can share that might help us to repeat that would be much appreciated.

[big-guy]

For Jan, Feb, March and April (so far), the top downloaded version of Gradle was 4.10.x with about 20% of all downloads. The 5.x releases bounce around a lot and take another 20%.

4.1 is the oldest top 10 release (~3% of all downloads), then 4.4/4.4.1 (~7%) and then 4.6 (~6%). Other than 4.10.x, no other 4.x version reaches the top 10 and hasn't for awhile.

I would consider 4.10.x, but that may be too aggressive for some.

[wilkinsona]

Thanks, @big-guy. So 40% of downloads are for Gradle 4.10.x or later. Of the other 4.x versions in the top 10 we don't support 4.1, and 4.4 and 4.6 account for a combined 13% of downloads. While 4.10.x may be a little bit aggressive, I don't think it's prohibitively so. After all, we'd happily move to the latest minor version of other dependencies in a minor release of Spring Boot.

Flagging for team attention to see if anyone disagrees and to discuss whether we should deprecate support for 4.x to encourage Spring Boot users to move to Gradle 5.

[snicoll]

@wilkinsona given the pace of releases I am +1 with that plan.