(crap, posted that too quickly)
Most of the ExecutionContext API doesn't apply to UDFs. Perhaps a new interface is needed? If the first (or last) parameter in the UDF method signature takes this new interface, Teiid would pass it in (I presume that Teiid is using typical reflection to invoke the UDF so this kind of introspection should be straightforward).
Log an issue?
Based upon the udf signature we'll pass the CommandContext and from there you can use the addWarning method.
Perfect. It's even doc'd. I should have RTFM.