When a user configures a Processor and uses the Expression Language, the UI provides wonderful contextual help when Ctrl+Space is pressed. However, this help is based purely on the Expression Language and the associated documentation.
It would be great to see the UI provide a list of Attributes that would likely make sense at that point in the flow.
There are lot of things to consider here. Attributes to suggest could be derived from the entire flow, or based on Attributes that have been seen on FlowFIles only by that Processor. Or based on the processor that introduced the data into the flow.
Eventually, this could even perhaps be driven by some process outside of NiFi, by running analytics against provenance data or what have you. Something like this would be quite a bit out of scope for now, though, and would be a later addition, but it's important to keep in mind for design considerations.
Additionally, Authorization needs to be considered when determining which Attributes to send.
We also don't want to fill up the Java Heap, so we would need some sort of LRU cache type of mechanism.
Also consider on restart of NiFi, or when a new processor is added to the graph, how do we provide context there for meaningful attributes?