Newline handling in thumbnail pattern settings

Is there an existing issue for this?

• I checked and did not find my issue in the already reported ones

Describe the bug

Darktable seems to honor newlines in the two thumbnail pattern settings ("pattern for the thumbnail extended overlay text" and "pattern for the thumnail tooltip (empty to disable)" in the "lightable" tab of the settings), but then only saves the first line so the patterns do not survive a restart.

Ideally, Darktable would preprocess the setting, save newlines as $(NL) (if need be), and restore $(NL) to the os-appropriate newline characters when loading the settings.

In any case, it should behave consistently and either limit input to one line or save/restore multi-line patterns correctly.

Affected version: Darktable 5.2.1 on linux (flatpak)

Steps to reproduce

1. go to the "lightable" tab in the settings windows
2. enter a mlti-line (with actual newlines, not $(NL)) in either of the last two fields
3. verify that the pattern is applied
4. close and restart Darktable
5. verify that the pattern was not saved correctly

Expected behavior

No response

Logfile | Screenshot | Screencast

No response

Commit

No response

Where did you obtain darktable from?

darktable.org / GitHub release

darktable version

5.2.1

What OS are you using?

Linux

What is the version of your OS?

tumbleweed (flatpak)

Describe your system

No response

Are you using OpenCL GPU in darktable?

None

If yes, what is the GPU card and driver?

No response

Please provide additional context if applicable. You can attach files too, but might need to rename to .txt or .zip

No response

Start by reproducing the issue in darktable's settings window using multiline values in the thumbnail extended overlay text and tooltip pattern fields. Check how those values behave before and after restarting the application; done means multiline patterns are either consistently rejected or preserved and restored correctly.