I've tried opening GIMP (.xcf) files with krita and I'm very happy to note that you can do this and work on them. This only works smoothly with no errors if the GIMP file has no layer groups or alpha masks (transparency masks).

If there are layer groups and/or alpha masks in the GIMP file then the following error message is displayed:
>------------------------------------------------------
Krita has encountered an internal error:

SAFE ASSERT (krita): "!newNode->parent()" in file /home/appimage/workspace/Krita_Release_Appimage_Build/krita/libs/image/kis_node.cpp, line 481

Please report a bug to developers!

Press Ignore to try to continue.
Press Abort to see developers information (all unsaved data will be lost)
<----------------------------------------------------

Pressing Abort causes krita to close with no 'developers information' displayed.

Pressing Ignore causes an identical error message to be displayed and the Ignore button must be pressed repeatedly depending on how many layer groups and masks there are in the GIMP file. After all these error messages have been Ignored then everything seems to work fine with groups and masks correctly present.
(All alpha masks are renamed as "effect" and all text layers are converted to paint layer images.)

Is this a bug in krita or should I not be trying to open GIMP files with krita?

Could be two things: a regression (loading xcf layer groups has been implemented) if you're loading a gimp 2.8 file, or, if loading a 2.10 file, a change in the xcf format that we cannot follow. Please make a bug and attach an xcf file to it that shows the issue.

Thanks for the rapid reply. ( It was GIMP 2.8 with krita 4.1.1 appimage). I'll do this fairly soon (I have a busy weekend) and will try it with GIMP 2.8 and 2.10 and the latest nightly build to check for any differences.

It was a false alarm.

I just tried it with the latest 4.2.0 pre-alpha appimage and opening GIMP 2.8 files works fine if they have layer groups and alpha masks.

Opening a GIMP 2.10 file gives a notification that krita can't open a GIMP file that is 2.9 or newer.

I think this emphasises the importance of using the latest nightly build when checking if a bug is present.

Thanks for testing!