Bug 570059 - ClassCastException in SelectionServiceListener
Summary: ClassCastException in SelectionServiceListener
Status: RESOLVED FIXED
Alias: None
Product: Platform
Classification: Eclipse Project
Component: UI (show other bugs)
Version: 4.14   Edit
Hardware: All All
: P3 normal (vote)
Target Milestone: ---   Edit
Assignee: Jens Lideström CLA
QA Contact:
URL:
Whiteboard:
Keywords: regression
Depends on:
Blocks:
 
Reported: 2021-01-04 13:40 EST by Hans-Erik Floryd CLA
Modified: 2021-01-09 14:24 EST (History)
2 users (show)

See Also:

Attachments
Sample plugin project (15.08 KB, application/zip)
2021-01-04 13:40 EST, Hans-Erik Floryd CLA 		no flags Details
View All Add an attachment (proposed patch, testcase, etc.)

Note You need to log in before you can comment on or make changes to this bug.
Description Hans-Erik Floryd CLA 2021-01-04 13:40:35 EST 
Created attachment 285170 [details]
Sample plugin project

The following code works for versions < 4.14:

		IObservableValue<Object> observe = WorkbenchProperties.singleSelection().observe(getSite().getService(ISelectionService.class));

		ISideEffect.create(new Runnable() {			
			@Override
			public void run() {			
				Object value = observe.getValue();
				System.out.println(value);
			}
		});

With version 4.14 and newer a ClassCastException is thrown when fireChanged is called in SelectionServiceListener.java as a result of clicking on e.g. the Project Explorer view:

java.lang.ClassCastException: class org.eclipse.ui.navigator.resources.ProjectExplorer cannot be cast to class org.eclipse.ui.ISelectionService(org.eclipse.ui.navigator.resources.ProjectExplorer is in unnamed module of loader org.eclipse.osgi.internal.loader.EquinoxClassLoader @1a25ef08; org.eclipse.ui.ISelectionService is in unnamed module of loader org.eclipse.osgi.internal.loader.EquinoxClassLoader @79316697)
	at org.eclipse.ui.internal.databinding.SelectionServiceListener.selectionChanged(SelectionServiceListener.java:64)
	at org.eclipse.ui.internal.e4.compatibility.SelectionService.notifyListeners(SelectionService.java:240)
	at org.eclipse.ui.internal.e4.compatibility.SelectionService.handleSelectionChanged(SelectionService.java:94)
	at org.eclipse.ui.internal.e4.compatibility.SelectionService.lambda$0(SelectionService.java:68)
	at org.eclipse.e4.ui.internal.workbench.SelectionAggregator$1.run(SelectionAggregator.java:123)
	at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:45)
[...]

This change in behaviour was introduced by commit d3c22327f2bdf89bebd15219c8f0f1d6671eb036.
Comment 1 Eclipse Genie CLA 2021-01-05 15:16:58 EST 
New Gerrit change created: https://git.eclipse.org/r/c/platform/eclipse.platform.ui/+/174299
Comment 2 Jens Lideström CLA 2021-01-05 15:17:35 EST 
Hello HE, and thanks for reporting with a such clear demonstration of the bug.

The problem is because SelectionListener uses a non-standard value as the source
argument to fireChange. This was not taken into consideration when adding type parameters, leading to ClassCastExceptions.

A fix has been pushed.
Comment 3 Hans-Erik Floryd CLA 2021-01-07 05:25:07 EST 
Hi Jens! Thanks for the quick fix. I see the build is failing although it seems unrelated to this patch?
Comment 4 Jens Lideström CLA 2021-01-07 05:38:32 EST 
(In reply to Hans-Erik Floryd from comment #3)
> I see the build is failing although it seems unrelated to this patch?

It seems like they have introduced a feature that fails builds during the master branch freeze time.

There is a master branch freeze time during a short period before each major release.