Sanity check of stage fetching requirements

[nuth]

1. Check if stage tries to request a document touched by itself.
2. Check if stage tries to request a document touched by a stage that doesn't exist.

[laserval]

Hm, what should this check result in? Warnings, errors, rejected configuration?

[ssimon]

A warning could help I guess, but I wouldn't reject the config. When you add several stages you don't want the order that you add your stages in to matter. But given a warning it would be easier to see why nothing is happening. Touched by itself seems like a strange thing to configure though..

I would say that checking if the query syntax was correct would be even more interesting. Writing "exist" instead of "exists" for example would result in the query being ignored without a warning or anything. Such an error could possibly reject the config in my opinion..