KSaveFile, QSaveFile, QFile

[Dominik Haumann]

Hi k-c-d / kwrite-devel,

Kate uses KSaveFile in KDE 4.10 to avoid data loss during save operations.
According to [1] KSaveFile will be deprecated in favor of QSaveFile with
kf5/Qt5.1.

Unfortunately, using KSaveFile introduces quite some regressions in Kate:

1. KSaveFile: Kate/kwrite makes a copy of a file while editing a hard link
   https://bugs.kde.org/show_bug.cgi?id=316240

2. KSaveFile: Unable to save file (777 permission) when the directory have 444
   https://bugs.kde.org/show_bug.cgi?id=312415

3. Kate changes owner of editing file (edit)
   https://bugs.kde.org/show_bug.cgi?id=316234 (likely KSaveFile issue)

Looking at the API/the code [1], QSaveFile seems to have the same behavior
as KSaveFile.

It looks like 1 (hard links) and 3 (file permissions/owner) are definitely
bugs in KSaveFile. Maybe QSaveFile is also affected (David?)?
The code in line 214 in [2] does look ok. Does it also set file owner?

2 (directory permissions) are hard to fix in KSaveFile. The only way out
would be to allow saving to the file directly in case of file permissions
are ok, but directory permissions are not.

What's the best way to fix that? I already see us writing yet another
KateFile class that tries to use K/QSaveFile, and in case of failure
falls back to QFile directly... doesn't sound too appealing to me :-)

Greetings,
Dominik

[1] https://codereview.qt-project.org/#change,41790
[2] https://codereview.qt-project.org/#patch,sidebyside,41790,10,src/corelib/io/qsavefile.cpp