Bug 117493 [content assist] CompletionRequestor#completionFailure(IProblem)) is ignored
This got introduced after 3.2 M1 (i.e. broken in 3.2 M2 and newer). If completion fails we now always show: "No completion available." instead of the real error text. Example: for (Iterator i=things.iterator(); i.<ctrl-space> // Iterator not yet imported)
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/text/java/JavaCompletionProcessor.java
private void filter(List proposals, TextContentAssistInvocationContext context) {
		/*
		 * TODO filtering is hard if the subjects come from multiple,
		 * often unknown sources. This method implements some heuristics
		 * that seem to work well.
		 */
		
		/*
		 * Duplicate filter:
		 *  Goal: remove hippie proposals for stuff that already have java proposals
		 *  Implementation:
		 *  - sort alphanumerically, sorting hippies on top
		 *  - remove any non-IJavaCompletionProposals that happen to have
		 *    the same prefix completion text as another proposal.
		 */
		Collections.sort(proposals, fAlphaComparator);
		IDocument document= context.getDocument();
		int offset= context.getInvocationOffset();
		ICompletionProposalExtension3 last= null;
		for (ListIterator it= proposals.listIterator(proposals.size()); it.hasPrevious();) {
			ICompletionProposal proposal= (ICompletionProposal) it.previous();
			ICompletionProposalExtension3 current= null;
			if (proposal instanceof ICompletionProposalExtension3) {
				current= (ICompletionProposalExtension3) proposal;
				if (last != null) {
					String lastCompletion= getPrefixCompletionText(document, offset, last);
					String curCompletion= getPrefixCompletionText(document, offset, current);
					if (lastCompletion.equals(curCompletion) && !(current instanceof IJavaCompletionProposal))
						it.remove();
				}