DataTable - ContextMenu - primefaces

Question

Primefaces Migration-Guide 5.3 to 6.0:
ContextMenu: p:contextMenu must be placed AFTER the target component (e.g. datatable) in the xhtml now.
I tried exactly that, but it' not working. No Menu at all.
Placing ContextMenu before dataTable: Menu is showing. Additional output on browser console:
ContextMenu targets a widget which is not available yet. Please place the contextMenu after the target component. targetWidgetVar: widget_base_cars
My Webshpere Liberty log:
...org.primefaces.webapp.PostConstructApplicationEventListener I Running on PrimeFaces 7.0
Java:
java.version = 1.8.0_102
Stripped down to primefaces showcase
<h:body>
<h1>Context Menu</h1>
<h2>ContextMenu: p:contextMenu must be placed AFTER the target component</h2>
<h:form id="base" >
<p:dataTable id="cars" var="car" value="#{dtContextMenuView.cars}" rowKey="#{car.id}" >
<f:facet name="header">
List with #{dtContextMenuView.numberOfCars} Items
</f:facet>
<p:column headerText="Id">
<h:outputText value="#{car.id}" />
</p:column>
<p:column headerText="Year">
<h:outputText value="#{car.year}" />
</p:column>
<p:column headerText="Brand">
<h:outputText value="#{car.brand}" />
</p:column>
<p:column headerText="Color">
<h:outputText value="#{car.color}" />
</p:column>
</p:dataTable>
<p:contextMenu for="cars" >
<p:menuitem value="Hello" />
<p:menuitem value="World" />
</p:contextMenu>
<h2>but it fails</h2>
</h:form>
</h:body>
I expect the menu to show on right click.
Is it a bug, or am i the bug?

Answer 1

I reproduced this testing around with PF 5.3/6.0/7.0. I'm with you as long as your p:dataTable is not selectable:
The p:contextMenu appears on rightclick when added above the p:dataTable element in xhtml. When added below, no context menu appears at all. But tbh.: is a context menu useful on a datatable which does not allow selection?
When making it selectable by adding the attributes
selection="#{myBean.selectedValue}" selectionMode="singel"
it behaves like this:
p:contextMenu below p:dataTable as suggested by migration guide: On rightclick, the clicked row is selected and context menu appears on it.
p:contextMenu above p:dataTable: on rightclick, context menu appears either, but the row is not selected.
So if p:contextMenu is added above the table, selection does not work as expected which must be the reason for the migration guide telling "add it below!".
Btw: I did not get that warning in my JavaScript console during my tests, don't know why.