A trivial nested class as a QObject derivative fools lupdate into thinking the parent class name is a namespace name that doesn't exist.

Error when lupdate parses MainWindow.cpp:

[ 22%] Generating /home/bill/src/cmake-test/translations/cmake-test_fr.ts
/home/bill/src/cmake-test/MainWindow.cpp:59: tr() cannot be called without context
/home/bill/src/cmake-test/MainWindow.cpp:59: Discarding unconsumed meta data
Updating '../../../src/cmake-test/translations/cmake-test_fr.ts'...
Found 0 source text(s) (0 new and 0 already existing)
[ 33%] Generating cmake-test_fr.qm
Updating '/home/bill/objdir/cmake-test/Debug/cmake-test_fr.qm'...
Generated 0 translation(s) (0 finished and 0 unfinished)

Explicit qualification of tr() as MainWindow::impl::tr() seems to work.