Check if existing database files are writable

[victoryforce]

It may happen that we will not have write access to the database restored from a backup or snapshot. Running darktable with a database that cannot be written to may result in incorrect operation, the cause of which will be difficult to diagnose.

Such cases have already been reported in issues, for example in #17187 and #17726.

[TurboGit]

Good for me, 5.2 merge window opens in one or two weeks.

[victoryforce]

Just a few days ago there was a post on the pixls forum, where the cause of the bug was also a read-only database. I vaguely remember a few more complaints about buggy behavior, which, as it is now clear, was a consequence of the inability to write data to the database.

Also, recently one of the users in my local community restored databases from snapshots without paying attention to access rights, and had similar problems.

What I want to emphasize is that this is not a very rare case, and probably many more users have encountered this problem, but did not report it. Or they reported strange behavior on social networks or on forums, but this never led to a correct diagnosis of this problem (and remained unnoticed by the dt devs).

So I'll get back to my favorite thing again, convincing you to break the unwritten rule of not including in a corrective release anything that adds new text to the GUI... After all, the user will not see this text during normal operation in darktable, but only when the start of the program needs to be stopped, because the program will not be able to work. Even if some translators do not translate this warning text before the 5.0.1 release, it is better to have it in English than not to stop the program from running.

[TurboGit]

Well we have lived with that for a long time, between 5.0.1 and 5.2 there is 4 months, I won't break the rule (not introducing new strings) for that :)

[victoryforce]

Sigh...

[zisoft]

Some Mac users (#17222 (comment)) have a problem with wrong permissions on ~/.config so darktable cannot create the ~/.config/darktable directory.

In this case, darktable closes silently because the GUI is not initialized at that early stage.