[p2-dev] How to limit expressions for IU requirements and filters

[Thomas Hallgren <thomas@xxxxxxx>]

Hi,
How do we want to limit the expression that can be used for the 
requirements and filters in our IU? Do we want to do that as a 
recommendation (i.e., documentation saying - don't use these 
constructs), or as a hard limit? The reason I ask is that we now have an 
API method with this signature:

public static IRequirement createRequirement(
   IMatchExpression<IInstallableUnit> requirement,
   IMatchExpression<IInstallableUnit> filter,
   int minCard, int maxCard, boolean greedy)

and even with the best separation in the world, we cannot really see how 
the 'requirement' or 'filter' was created. What parser was used, what 
factory, etc. What we can do, is to let this method use a visitor that 
triggers on expressions that are not allowed. Do we want that? If so, 
what expressions do we want to allow/prevent?

- thomas