I'm about to start modernization of a very old Eclipse RCP application, which uses Eclipse Helios (2011) as an IDE and runs on Java 1.6.
The first step I'd like to do is to take a newer version of Eclipse IDE and force it to load that ancient project. What I came across is the following problem: old plugin dependencies are present:
org.eclipse.ui (3.203.100.v20230417-1307)
but their minor versions have gone through a lot, too. What I need, for the example above, is:
org.eclipse.ui (3.6.2.M20110203-1100)
Is it really the case, that I can't get core plugin versions in any version I desire, only in the one bundled with the IDE?
You use a "Target Platform" to specify which version of plug-ins to use. It is recommended that you always do this even when developing for the current Eclipse as it give you better control of exactly what is available.
Target Platforms are set up in the Preferences (Settings on macOS) in the "Plug-in Development > Target Platform" page. You can have multiple target platforms but only one is active at a time.
The Eclipse archive has downloads for every version of Eclipse. These can be used as target platforms.
Don't try and mix plug-ins from different Eclipse versions.