A new load_layer expression function has been made available (exclusively for Processing expressions for the time being), which allows the loading of a map layer using a source string and provider name.
It is designed to allow the use of the expression functions which directly reference map layers (such as the aggregate functions) with a hardcoded layer path.
This permits the usage of these functions to be used outside of a project (such as via the qgis_process tool) and perform operations such as utilizing complex aggregate functions in the refactor fields algorithm via the qgis_process utility without creating a temporary project for data manipulation.
This feature was funded by the Research Institute for Nature and Forest, Flemish Govt
This feature was developed by Nyall Dawson