SetFileInformationByHandle requires opening the file with the DELETE access flag. In turn, opening a file with this flag means everyone that wants to use the file at the same time has to open the file as FILE_SHARE_DELETE.

Because QLockFile today doesn't the SHARE_DELETE flag, we cannot make the change to use SetFileInformationByHandle today because it would then suddenly become impossible for old and new versions of Qt to use QLockFile for the same file.

By making QLockFile open the file with SHARE_DELETE today, however, we can give ourselves a longer tail of versions of Qt that will be able to coexist with Qt 7 or Qt 6.x, that does make this change.