The attached example should render the numbers 0-29 in 3 columns and 10 rows, but one of the columns is defined by a composite component and isn't rendered.

Another version of my test case, noticed a typo in my xmlns for the composite comps, that would cause this test to fail even if the nested column problem didn't exist.

Fixed the typo, nesting issue persists as expected.

Screenshot shows ui:debug output.

The composite component is a child of a UINamingContainer (likely part of the composite component implementation technique). Usually this would not be a problem, but h:dataTable is looking for immediate UIColumn children, not UIColumn ancestors, and it does not discover the columns. It would be possible to implement ice:dataTable to search for nested columns. Another option would be to implement this particular component using the Java API rather than Facelet composition.

Removing ICEfaces from the test case does not remove the undesired behavior – this is not an ICEfaces bug.

I'd read that there is an attribute "componentType="some.java.Class"" of composite:interface that can be used to define the type of the Facelet composed component, but I could never find an example of its use.

If this exists wouldn't it be possible keep our current Facelet composite columns and change its componentType to a subclass of HtmlColumn?

Also on a similar topic was:
http://weblogs.java.net/blog/cayhorstmann/archive/2010/01/30/composite-input-components-jsf

Which may be useful as it demos implementing composite components using UIInput subclasses rather than UINamingContainer, could the same could be done with a UIColumn subclass?

That looks like an excellent technique. Please try it out.

Another approach would be to implement a TagHandler, but that will be more complex – the componentType attribute should allow the Renderer to remain a facelet while the backing component is the desired class. A custom TagHandler would require implementation of all three parts (tag, Component, and Renderer).

After using a backing component to identify our composite component as UIColumn to the DataTable, our composite component appears to behave just a a regular h:column would.

However for composite components to be worthwhile, we need to make use of the cc:insertChildren tag; the composite component tag responsible for the copying of using-page tag-children into the CC. This is performed by the RelocateChildrenListener (a RelocateListener subclass) listening for the PostAddToViewEvent.

Unfortunately, UIColumn already performs a relocation like this by default, duplicating its contents repeatedly into the respective column of each row. This is performed by com.sun.faces.renderkit.html_basic.BaseTableRenderer during component encoding, which appears to occur after PostAddToViewEvent.

These two events clash and cause the unpredictable encoding of column and CC contents. With cc:insertChildren removed, the default Column behaviour works. With it present, sometimes the default Column behaviour will display on a re-render (ex. after pressing a button), but normally nothing appear in the column cells.

The children of the using page appear to be being blanked by the cc:insertChildren event, and when the Column encoding gets to them, there is nothing to render. This is judging from the firing order of the events and the many additional calls to getChildrenCount() (of my backing component) that all return 0, which aren't present when cc:insertChildren is absent.

Failing that a solution can be found to the column issues, a workaround could be using two tag-libs in the ice-cc jar, one using the new composite component interface sans tables, and one using the older style table components.

Moving to beta 2, doesn't effect the compat version.

working as expected now with JSF 2.1