Duplicate output

[dpriskorn]

Description of problem

The validator outputs the same validation errors multiple times

E.g.

[
     {
       "type": "MissingProperty",
       "property": "[http://www.wikidata.org/prop/direct/P137](https://www.wikidata.org/prop/direct/P137)"
     },
     {
       "type": "MissingProperty",
       "property": "[http://www.wikidata.org/prop/direct/P625](https://www.wikidata.org/prop/direct/P625)",
       "valueExpr": {
         "type": "NodeConstraint",
         "datatype": "http://www.w3.org/2001/XMLSchema#coordinate"
       }
     }
   ],
   [
     {
       "type": "MissingProperty",
       "property": "[http://www.wikidata.org/prop/direct/P137](https://www.wikidata.org/prop/direct/P137)"
     },
     {
       "type": "MissingProperty",
       "property": "[http://www.wikidata.org/prop/direct/P625](https://www.wikidata.org/prop/direct/P625)",
       "valueExpr": {
         "type": "NodeConstraint",
         "datatype": "http://www.w3.org/2001/XMLSchema#coordinate"
       }
     }
   ],

URL to affected spec or repo:
See details under second try here: https://www.wikidata.org/wiki/User:So9q/shexjs#Usage

What happened (e.g., it crashed)?:
Unexpected duplicate output

Expected behavior (e.g., it shouldn't crash):
No duplicate output

Optional, steps to reproduce:

1. ...

[ericprud]

The fact that they're in an array means they showed up through some disjunction (typically an EachOf, but not exclusively).

It would be nice to

1. work out some minimal and realistic use cases
2. improve nfax-threaded-nerr to eliminate redundancies
3. make it so e.g. the following use case would generate consistent and minimal error reports:

Schema

<Person> {
  ( :name . ; addr . )
|
  ( :name . )
}

Data

<Alice> :foo 1 .