Launch Configurations: Determine launcher classpath and/or launcher class

[bdorninger]

Hi

I have a target platform made up from a very very old Eclipse application (org.eclipse.core.runtime 3.2.0) plus a few own bundles/plugins.
It serves as a base for applications with additional custom plugins, which still need to be maintained.
Customer used a very old Eclipse IDE for maintaining up to now, but wants to switch to a newer version

Thus I installed a bare Eclipse 12/24 for Plugin developers and added my target platform.
Default target JVM is Java 17, Eclipse itself runs with the provided Open JDK 21

However, when I create a launch configuration for an Eclipse Application, Eclipse uses the launcher lib of the installed IDE (-classpath "C:\eclipse1224\plugins\org.eclipse.equinox.launcher_1.6.900.v20240613-2009.jar;"), but on the other hand determines the launcher class to be "org.eclipse.core.launcher.Main".
But that library only contains a class "org.eclipse.equinox.launcher.Main"

How does Eclipse determine the launcher classpath and the main class defaults in a Eclipse Application launch config, as a user cannot set these values?

So I end up with a ClassNotFoundException, no matter if i set a classpath in the launch configuration (either program od VM args) or try the same in the target platform configuration.

Error: Could not find or load main class org.eclipse.core.launcher.Main
Caused by: java.lang.ClassNotFoundException: org.eclipse.core.launcher.Main

The only workaround: In my custom Installed JRE for Java 17 I added the -Xbootclasspath/a:path/to/my/other/launcher/lib.jar, which contains a "org.eclipse.core.launcher.Main". Then everything works as expected

See the non-working "Show Command Line" output below

C:\Program Files\Java\jdk-17\bin\javaw.exe
--add-opens=java.base/java.net=ALL-UNNAMED
-Dpmp.dtr.config=datatypesSM.ini
-Declipse.pde.launch=true
--add-modules=ALL-SYSTEM
-Dfile.encoding=UTF-8
-Dstdout.encoding=UTF-8
-Dstderr.encoding=UTF-8
-classpath "C:\eclipse1224\plugins\org.eclipse.equinox.launcher_1.6.900.v20240613-2009.jar;"
-XX:+ShowCodeDetailsInExceptionMessages org.eclipse.core.launcher.Main
-launcher "C:\Users\lzu\eclipse1224-workspace\.metadata\.plugins\org.eclipse.pde.core\.bundle_pool\eclipse.exe"
-name Eclipse
-showsplash 600
-application at.foo.pmp.Scheduler
-data "C:\Users\lzu\eclipse1224-workspace/../runtime-LZU-SM"
-configuration file:C:/Users/lzu/eclipse1224-workspace/com.foo.test.config/configuration/
-debug