[QGIS-Developer] Refactor fields processing algorithm and expressions

[Andreas Neumann]

Hi,

I am running into troubles using expressions in the "Refactor fields" 
processing provider.

E.g. I have a date field and would like to reformat it in german format:

format_date("erfassungsdatum",'dd.MM.yyyy')

Although I am 100% certain that the above expression is syntactically 
correct, the expression builder insists that the expression is invalid 
and I can therefore not apply and save this expression.

Is this a known limitation because the model does not know which layer 
it is tied to?

Are there any workarounds?

Thanks,

Andreas