The compiler generated copy constructor and assignment operator are wrong.
This could easily be fixed by implementing them manually, but a) they are
not needed, and b) the semantics would be unclear (should the copy point
to a new temp file or not?), so it is better to forbid them.
- The TempFile class guarantees to generate a file name, we are not limited to
100 tries of a predictable scheme anymore, which could break if LyX
frequently crashes.
- The temp file name generation has no race condition against another LyX
instance in the same directory anymore.
- Symlinks survive saving again (regression of 10364082c8).
FileName::tempName() is not thread safe, since the QTemporaryFile object is
immediately deleted after creating it. Therefore, another thread could create
the same temporary file in the time span before the user of FileName::tempName()
recreates it. This is not as theoretical as it may look: I observed that
repeated creation and deletion of QTemporaryFile objects always use the same
name.
This problem is solved by the new class TempFile which should be used like
QTemporaryFile itself.
