When calling lupdate on a file that uses QT_TR_NOOP in a constructor for a static QString it will fail to find the context. So a line like:

const QString MyClass::str1( QT_TR_NOOP( "Produces warning" ) );

will output:

tr() cannot be called without context

when using lupdate. Whereas if the result of QT_TR_NOOP is used in an assignment to the QString in the same location it is fine.