Misleading multiport warning and NullPointerException in diagram synthesis

[cmnrd]

target Cpp

public preamble {=
  inline std::size_t foo() { return 4; }
=}

reactor Src {
  output[4] out: void
}

reactor Sink {
  input[{=foo()=}] in: void
}

main reactor Minimal {
  src = new Src()
  sink = new Sink()
  src.out -> sink.in
}

The above legal C++ program produces a misleading warning message: "Left width 4 does not match right width 0". This probably comes from a false assumption made somewhere in the instance graph.

Also, the diagram synthesis fails for this program with a NullPointerException.

[soerendomroes]

Just for the record, the exception.

Java.lang.NullPointerException: Cannot read field "_interleaved" because "src" is null
	at org.lflang.generator.ReactorInstance.connectPortInstances(ReactorInstance.java:923)
	at org.lflang.generator.ReactorInstance.establishPortConnections(ReactorInstance.java:987)
	at org.lflang.generator.ReactorInstance.<init>(ReactorInstance.java:888)
	at org.lflang.generator.ReactorInstance.<init>(ReactorInstance.java:105)
	at org.lflang.diagram.synthesis.LinguaFrancaSynthesis.transform(LinguaFrancaSynthesis.java:315)
	at org.lflang.diagram.synthesis.LinguaFrancaSynthesis.transform(LinguaFrancaSynthesis.java:1)
	at de.cau.cs.kieler.klighd.syntheses.AbstractDiagramSynthesis.transform(AbstractDiagramSynthesis.java:220)
	at de.cau.cs.kieler.klighd.syntheses.ReinitializingDiagramSynthesisProxy.transform(ReinitializingDiagramSynthesisProxy.java:289)
	at de.cau.cs.kieler.klighd.ViewContext.update(ViewContext.java:454)
	at de.cau.cs.kieler.klighd.ViewContext.update(ViewContext.java:389)
	at de.cau.cs.kieler.klighd.ViewContext.update(ViewContext.java:373)
	at de.cau.cs.kieler.klighd.LightDiagramServices.updateDiagram(LightDiagramServices.java:109)
	at de.cau.cs.kieler.klighd.LightDiagramLayoutConfig.performUpdate(LightDiagramLayoutConfig.java:425)
	at de.cau.cs.kieler.klighd.ui.view.DiagramView.doUpdateDiagram(DiagramView.java:1122)
	at de.cau.cs.kieler.klighd.ui.view.DiagramView$10.runInUIThread(DiagramView.java:1007)
	at org.eclipse.ui.progress.UIJob.lambda$0(UIJob.java:148)
	at org.eclipse.swt.widgets.RunnableLock.run(RunnableLock.java:40)
	at org.eclipse.swt.widgets.Synchronizer.runAsyncMessages(Synchronizer.java:132)
	at org.eclipse.swt.widgets.Display.runAsyncMessages(Display.java:5040)
	at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:4520)
	at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$5.run(PartRenderingEngine.java:1155)
	...

The source RuntimeRange seems to be null here. In Epoch you can find the stack trace in the "Error Log" view.
In VS Code it is one logged to the notifications without browserifying the strings properly.
Both is not ideal. In Epoch, this should be logged to the console to be able to jump to the corresponding class. In VS Code it should also be logged to the output view.

[a-sr]

As this is an issue with the graph analysis (ReactorInstance) and probably not the diagram, I will remove the diagram label from this issue.