Qt4 code has been identidifed by
git grep -l 'QT_VERSION.*\(0x050000\|0x04\)' src
Uses of QT_VERSION_CHECK have been checked too.
been used to remember what places need further work.
Then remaining Qt4 references have been searched using
git grep -i qt4
git grep -i 'qt 4'
and relevant issues have been either fixed or noted in the new
TODO.killqt4 file.
In particular, the directory frontends/qt4 is renamed to frontends/qt.
Many configurations file have to be updated. All mentions of qt4 in
the source have been audited, and changed to qt if necessary.
The only part that has not been updated is the CMake build system.