Undefined function '_theme'

This looks like to be about a feature that was not ported yet. In the D7 version of Feeds Extensible Parsers, you can enable the debug option per source:

After import, the value of each XML source is displayed:

And this is how a XML Xpath source can be configured in the D8+ version:

No "debug" option there.

Note: not only the XML Xpath parser, but every parser in the D7 version of Feeds Extensible Parsers had this debug feature.

So the action is: we need to decide if we want to port the "debug" feature. Feeds now also has a module called Feeds Log and that can be used for debugging imports too.

I think in order to get phpstan be passing, it would be good to remove the dead code. And then perhaps create a new issue to re-add the debug feature from the D7 version - if we still want it. Maybe we don't need it per se?

Yes, I would vote to remote the non-functional code for now, and then if somebody really wants it, a new feature request would be opened. But as you already mentioned, Feeds Log exists, so it would probably be best to improve that if it isn't sufficient for whatever reason.

I removed the debug and theme function. Let's see what the tests think of that.

Tests are passing! Merged.

Automatically closed - issue fixed for 2 weeks with no activity.