ClassCastException when ctrl+hover over a 'case' literal

[nlisker]

public class Hover {

	void do2() {
		record R(int i, long l) {}

		R r = new R(1, 1);
		switch (r) {
			case R(_, long l) -> {}
			case R r2 -> {}
		}
	}
}

Hold Ctrl and hover over the second case literal. The case will become clickable as if it's a method or parameter, which is wrong. Then, while still holding Ctrl, move the mouse to the first case label. A bunch of these errors will be thrown:

Unhandled event loop exception

java.lang.ClassCastException: class org.eclipse.jdt.core.dom.VariableDeclarationFragment cannot be cast to class org.eclipse.jdt.core.dom.SingleVariableDeclaration (org.eclipse.jdt.core.dom.VariableDeclarationFragment and org.eclipse.jdt.core.dom.SingleVariableDeclaration are in unnamed module of loader org.eclipse.osgi.internal.loader.EquinoxClassLoader @17a0846)
	at org.eclipse.jdt.core.dom.TypePattern.getPatternVariable(TypePattern.java:242)
	at org.eclipse.jdt.internal.corext.dom.ASTFlattener.visit(ASTFlattener.java:2021)
	at org.eclipse.jdt.internal.corext.dom.ASTFlattener.visitPattern(ASTFlattener.java:1451)
	at org.eclipse.jdt.internal.corext.dom.ASTFlattener.visit(ASTFlattener.java:1427)
	at org.eclipse.jdt.core.dom.RecordPattern.accept0(RecordPattern.java:231)
	at org.eclipse.jdt.core.dom.ASTNode.accept(ASTNode.java:3312)
	at org.eclipse.jdt.internal.corext.dom.ASTFlattener.visit(ASTFlattener.java:1669)
	at org.eclipse.jdt.core.dom.SwitchCase.accept0(SwitchCase.java:212)
	at org.eclipse.jdt.core.dom.ASTNode.accept(ASTNode.java:3312)
	at org.eclipse.jdt.internal.corext.dom.ASTNodes.asString(ASTNodes.java:366)
	at org.eclipse.jdt.internal.ui.javaeditor.JavaElementHyperlinkDetector.findSwitchCaseTarget(JavaElementHyperlinkDetector.java:290)
	at org.eclipse.jdt.internal.ui.javaeditor.JavaElementHyperlinkDetector.detectHyperlinksCached(JavaElementHyperlinkDetector.java:116)
	at org.eclipse.jdt.internal.ui.javaeditor.JavaElementHyperlinkDetector.lambda$0(JavaElementHyperlinkDetector.java:84)
	at org.eclipse.jdt.internal.core.JavaModelManager.cacheZipFiles(JavaModelManager.java:5694)
	at org.eclipse.jdt.internal.core.JavaModelManager.callReadOnly(JavaModelManager.java:5683)
	at org.eclipse.jdt.core.JavaCore.callReadOnly(JavaCore.java:6150)
	at org.eclipse.jdt.internal.ui.javaeditor.JavaElementHyperlinkDetector.detectHyperlinks(JavaElementHyperlinkDetector.java:84)
	at org.eclipse.ui.texteditor.HyperlinkDetectorRegistry$HyperlinkDetectorDelegate.detectHyperlinks(HyperlinkDetectorRegistry.java:81)
	at org.eclipse.jface.text.hyperlink.HyperlinkManager.findHyperlinks(HyperlinkManager.java:289)
	at org.eclipse.jface.text.hyperlink.HyperlinkManager.findHyperlinks(HyperlinkManager.java:262)
	at org.eclipse.jface.text.hyperlink.HyperlinkManager.mouseMove(HyperlinkManager.java:457)
	at org.eclipse.swt.widgets.TypedListener.handleEvent(TypedListener.java:229)
	at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:91)
	at org.eclipse.swt.widgets.Display.sendEvent(Display.java:4368)
	at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1173)
	at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:4166)
	at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3754)
	at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$5.run(PartRenderingEngine.java:1151)
	at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:339)
	at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.run(PartRenderingEngine.java:1042)
	at org.eclipse.e4.ui.internal.workbench.E4Workbench.createAndRunUI(E4Workbench.java:153)
	at org.eclipse.ui.internal.Workbench.lambda$3(Workbench.java:663)
	at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:339)
	at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:570)
	at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:173)
	at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:178)
	at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:208)
	at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:143)
	at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:109)
	at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:439)
	at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:271)
	at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
	at java.base/java.lang.reflect.Method.invoke(Method.java:580)
	at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:668)
	at org.eclipse.equinox.launcher.Main.basicRun(Main.java:605)
	at org.eclipse.equinox.launcher.Main.run(Main.java:1481)

From the stack trace, I'm not sure if this is a bug in jdt.core or jdt.ui, but the exception itself happens in core.

eclipse.buildId=4.34.0.I20241101-1800
java.version=22
java.vendor=Oracle Corporation
BootLoader constants: OS=win32, ARCH=x86_64, WS=win32, NL=en_US

[srikanth-sankaran]

@subyssurendran666 would you like to work on this ?

[subyssurendran666]

With pleasure! Could you please assign this to me?

@subyssurendran666 would you like to work on this ?

[subyssurendran666]

I believe this issue is related to JDT.UI

In Java 22, a new feature called unnamed variables and patterns has been introduced. To accommodate this, certain changes have been incorporated into JDT.Core. For example, in a case literal like case R(_, long l) -> {}, the first parameter of the record is an unnamed pattern (_). In JDT.Core DOM, unnamed patterns are handled by TypePattern. Here, the PatternVariable of the TypePattern is a VariableDeclarationFragment (since it has no type). However, the visit method in ASTFlattener attempts to cast the patternVariable to SingleVariableDeclaration through getPatternVariable(), which is applicable only for Java version below 22.

This issue has been addressed by implementing a new method called getPatternVariable2(). I believe the code below, or a similar approach, should resolve the issue.

 public boolean visit(TypePattern node) {
		if (ASTHelper.isPatternSupported(node.getAST())) {
                         if (node.getAST().apiLevel() < ASTHelper.JLS22) {
			    node.getPatternVariable().accept(this);
                         } else {
                              node.getPatternVariable2().accept(this);
                         }
		}
		return false;
}

[nlisker]

So should this be transferred to jdt.ui?

[srikanth-sankaran]

@subyssurendran666 - the code you cite is in jdt-core, no ?

[subyssurendran666]

No @srikanth-sankaran, the ASTFlattener(which is in JDT.UI) is calling the getPatternVariable() API from the DOM.

[srikanth-sankaran]

@noopur2507 - Can you confirm this is a JDT.UI problem ? TIA

[noopur2507]

Hold Ctrl and hover over the second case literal. The case will become clickable as if it's a method or parameter, which is wrong.

The 'case' becoming clickable is a feature that allows you to click the 'case' to jump to the corresponding 'switch' keyword. This is useful for quickly jumping to the beginning of a long switch-case.

Then, while still holding Ctrl, move the mouse to the first case label. A bunch of these errors will be thrown:

To be fixed.

[noopur2507]

I believe this issue is related to JDT.UI

Thanks for the analysis, Suby. I will make the corresponding change in UI.

However, few changes are required in JDT Core as well:

• The Javadoc of both APIs i.e. TypePattern.getPatternVariable() and TypePattern.getPatternVariable2() is same and not clear regarding this difference.
• The methods in JDT UI's ASTFlattener are kept in sync with JDT Core's org.eclipse.jdt.internal.core.dom.NaiveASTFlattener. Hence, the change should be done in NaiveASTFlattener as well and then synced to ASTFlattener.

[subyssurendran666]

I believe this issue is related to JDT.UI

Thanks for the analysis, Suby. I will make the corresponding change in UI.

However, few changes are required in JDT Core as well:

• The Javadoc of both APIs i.e. TypePattern.getPatternVariable() and TypePattern.getPatternVariable2() is same and not clear regarding this difference.
• The methods in JDT UI's ASTFlattener are kept in sync with JDT Core's org.eclipse.jdt.internal.core.dom.NaiveASTFlattener. Hence, the change should be done in NaiveASTFlattener as well and then synced to ASTFlattener.

Thank you, @noopur2507 for your insights on JDT.Core. I'll make the necessary arrangements in JDT.Core.

[nlisker]

The 'case' becoming clickable is a feature that allows you to click the 'case' to jump to the corresponding 'switch' keyword. This is useful for quickly jumping to the beginning of a long switch-case.

What an interesting feature. Didn't know about it.

[subyssurendran666]

I believe this issue is related to JDT.UI

Thanks for the analysis, Suby. I will make the corresponding change in UI.

However, few changes are required in JDT Core as well:

• The Javadoc of both APIs i.e. TypePattern.getPatternVariable() and TypePattern.getPatternVariable2() is same and not clear regarding this difference.
• The methods in JDT UI's ASTFlattener are kept in sync with JDT Core's org.eclipse.jdt.internal.core.dom.NaiveASTFlattener. Hence, the change should be done in NaiveASTFlattener as well and then synced to ASTFlattener.

@noopur2507 this has been implemented though eclipse-jdt/eclipse.jdt.core#3261

[iloveeclipse]

Reopening, after the change was reverted via eclipse-jdt/eclipse.jdt.core#3529