StateNode#handleOnAttach exception message should be improved

I ran into this exception: https://github.com/vaadin/flow/blob/907cbbd59612ac2e31daf5c1566fb48529d75200/flow-server/src/main/java/com/vaadin/flow/internal/StateNode.java#L705-L706 When you get it, the stack trace gives you no hint what this is about:

Unexpected exception occured: java.lang.IllegalStateException: Can't change id once it has been ass
igned
        at com.vaadin.flow.internal.StateNode.handleOnAttach(StateNode.java:705)
        at com.vaadin.flow.internal.StateNode.lambda$onAttach$1(StateNode.java:312)
        at com.vaadin.flow.internal.StateNode.visitNodeTreeBottomUp(StateNode.java:669)
        at com.vaadin.flow.internal.StateNode.onAttach(StateNode.java:311)
        at com.vaadin.flow.internal.StateNode.setParent(StateNode.java:270)
        at com.vaadin.flow.internal.nodefeature.NodeFeature.attachPotentialChild(NodeFeature.java:78)
        at com.vaadin.flow.internal.nodefeature.StateNodeNodeList.add(StateNodeNodeList.java:53)
        at com.vaadin.flow.internal.nodefeature.ElementChildrenList.add(ElementChildrenList.java:42)
        at com.vaadin.flow.dom.impl.AbstractNodeStateProvider.insertChild(AbstractNodeStateProvider.java:102)
        at com.vaadin.flow.dom.Node.insertChild(Node.java:250)
        at com.vaadin.flow.dom.Node.appendChild(Node.java:141)
        at com.vaadin.flow.data.provider.AbstractComponentDataGenerator.registerRenderedComponent(AbstractComponentDataGenerator.java:128)
        at com.vaadin.flow.data.provider.ComponentDataGenerator.generateData(ComponentDataGenerator.java:84)
        at com.vaadin.flow.data.provider.CompositeDataGenerator.lambda$generateData$0(CompositeDataGenerator.java:47)
        at java.lang.Iterable.forEach(Iterable.java:75)
        at com.vaadin.flow.data.provider.CompositeDataGenerator.generateData(CompositeDataGenerator.java:47)
        at com.vaadin.flow.data.provider.DataCommunicator.generateJson(DataCommunicator.java:660)
        at java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:193)
        at java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:193)
        at java.util.stream.IntPipeline$4$1.accept(IntPipeline.java:250)
        at java.util.stream.Streams$RangeIntSpliterator.forEachRemaining(Streams.java:110)
        at java.util.Spliterator$OfInt.forEachRemaining(Spliterator.java:693)
        at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:482)
        at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:472)
        at java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:708)
...

Expected behavior: it should at least tell, what kind of id is the problem.

[pleku]

I tried to recreate this exception using Vaadin 14.5.1

@MathiasAugstein please note that 14.5 has been unsupported since May 2021 , I’d advice you to update to the latest minor version 14.7.

[TatuLund]

The exception is still throw in other case, but the text has been changed to give better hint, what is the likely cause so that it is easier to address the issue in application code.

"The component '"
                    + component.getClass()
                    + "' is already attached to a UI instance which differs "
                    + "from the conainer's UI instance. It means that the component instance is "
                    + "reused instead being produced every time on 'createComponent' call."
                    + " Check whether the component instance is a singleton or has inappropriate Spring scope.");

OR, logging warning

        if (renderedComponent.getParent().isPresent()) {
            LoggerFactory.getLogger(ComponentDataGenerator.class).warn(
                    "The 'createComponent' method returned a component '{}' which already has a parent."
                            + " It means that most likely your component renderer '{}' class is implemented incorrectly",