"Can't find common super class" error

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1

I’m trying to obfuscate an Eclipse RCP and the following error is popping up:

[proguard] Unexpected error while performing partial evaluation:
[proguard] Class = [stQuote/disCurve/j]
[proguard] Method = [chartMouseMoved(Lorg/jfree/chart/ChartMouseEvent;)V]
[proguard] Exception = [proguard.evaluation.IncompleteClassHierarchyException] (Can't find common super class of [org.jfree.experimental.swt.SWTGraphics2D] (with 1 known super classes: org.jfree.experimental.swt.SWTGraphics2D) and [stCore.db.Security] (with 4 known super classes: stCore.db.Security, java.lang.Object, java.util.Observable, stCore.db.PersistentObject))

The SWTGraphics2D and Security classes have nothing in common (except for the Java Object super-class, of course). The latter is one of our own classes and the former is from the jFreeChart library, that comes from a .jar.

Our plugins structure, simplified here, is this:
+ main feature
| - stCore plugin
| - stQuote plugin : the plugin being obfuscated
| - stLibs plugin : the plugin where jFreeChart .jar is

The point on our code that those two classes are used is a method that receives a Security as a parameter and instantiates a SWTGraphics2D. For testing purposes, if I modify this method to remove the Security paramater, the obfuscation works as expected.

Any ideas of what might be happening here, or how I could dig deeper to discover the source of this strange behavior?

2

Follow up to add some more information.
I made a change on our code and now the error is gone.

Our original code, simplified:
private ourMethod( Security theSecurity ) {
// some smart code

TextTitle text = new TextTitle();
text.setText( theSecurity.getDescription() );
Graphics2D g2d = new SWTGraphics2D();
Size2D size = text.arrange( g2d );
g2.dispose();

// more smart code
}

The refactored code:

private ourMethod( Security theSecurity ) {
// some smart code

TextTitle text = new TextTitle();
text.setText( theSecurity.getDescription() );
Size2D size = getSize( text )

// more smart code
}

private Size2D getSize( TextTitle text ) {
Graphics2D g2d = new SWTGraphics2D();
Size2D size = text.arrange( g2d );
g2.dispose();
return size;
}

So far, this solution works for us and we’ll stick to it.
But it still bugs me why the original code leads to an error.