Hi Tony,
I suspect that in your original message you have the wrong link still - that may be the cause of some of the confusion that seems to be in this conversation. The commit you reference is a change only to tests and I assume that you are not shipping tests nor really need to rerun them as part of your RCP application. The platform change that actually changes the version of Ant that is shipped is
https://git.eclipse.org/r/163228 - along with some earlier updates that point at newer orbit URLs that include the new ant version.
If you are building your own app, your app probably has its own .target or equivalent in the pom file and in that file you can point at the new orbit (2020-06), along with the older platform (4.15) version. You may need some version constraints in your .product file to make sure that only the correct version of ant is included.
On to some of your other questions in case you have this or other reasons to rebuild the platform:
> Still just wondering if it is expected that such a change would be needed.
I think the change is needed as once a version of Eclipse is released its branch is left in a somewhat broken state because the I-build deps are deleted. It may be nice if the branches for completed versions were left in a buildable state, but that is not a priority for active developers, so someone would have to do that work. Please note that this problem exists whenever you want to build an older version of Eclipse. For example with the multi-repo builds of Eclipse it can be quite hard to build an old version of Eclipse to, for example, run git bisect to identify a problem. During development lots of old I-builds are left so that you can do that, but once a release is done those are removed.
I hope the above helps. Let me know if I have misunderstood the direction you are aiming for.
Jonah
