eclipse external tools configurations -> referenced library in classpath does not exist: org.eclipse.swt

Question

After updating to the latest eclipse mars release

Version: Mars Release Candidate 1 (4.5.0RC1)
Build id: 20150521-1252

I am not able to start any Ant Script. It always results in the following error:

First I checked if the path is really correct, and made sure that the specific jar org.eclipse.swt.win32.win32.x86_64_3.104.0.v20150513-1901.jar exists at the given location, which it does. After some digging I noticed the following within the external tools configurations:

Somehow I think eclipse is not able to resolve the classpath with the given '%20' tag within the url to the library. Usually there is just a blank. Restoring the defaults always fills in the '%20' for this specific library.

So I created a copy of eclipse at a location without blanks and all works fine again.

Unfortunatly I would prefer keeping the location at it is, so is there a way to correctly resolve the classpath for Additional Tasks & Support?

Answer 1

There is one other "fix" that's basically an easier workaround.

If you go to your Ant build configuration (under External Tools, then highlight your configuration and select the JRE tab) and change from running an external JRE to the top button, that is, "Run in the same JRE as the workspace", this will make it work.

Answer 2

This is a known bug in Eclipse Mars:

https://bugs.eclipse.org/bugs/show_bug.cgi?id=470390

Update: Eclipse 4.5.1 was released on October the 2nd and the bug has been fixed. An Eclipse update will resolve this issue.