fix: handle circular references in traverseMore

Processor.js

@@ -1,3 +1,4 @@
+import TermSet from '@rdfjs/term-set'
 import Edge from './Edge.js'
 import * as ns from './lib/namespaces.js'
 
@@ -248,6 +249,7 @@ class Processor {
   static traverseMore ({ ptrs, end, start, subjects, predicates, objects, graphs, callback } = {}) {
     let result = [...ptrs]
     let current
+    let last
 
     do {
       current = []
@@ -259,8 +261,14 @@ class Processor {
         ]
       }
 
+      if (last) {
+        current = current.filter(ptr => !last.has(ptr.term))
+      }
+
       ptrs = current
       result = [...result, ...current]
+
+      last = new TermSet(result.map(ptr => ptr.term))
     } while (current.length > 0)
 
     return result

test/Processor.test.js

@@ -499,6 +499,38 @@ describe('Processor', () => {
 
       grapoiEqual(result, expectedQuads)
     })
+
+    it('should stop traversing if the start and end of an edge are the same', () => {
+      const { expectedQuads, predicates, ptr } = datasets.traverseZeroOrMoreSelfRef()
+
+      const result = Processor.traverseMore({
+        ptrs: [ptr],
+        end: 'object',
+        start: 'subject',
+        subjects: [null],
+        predicates,
+        objects: [null],
+        graphs: [null]
+      })
+
+      grapoiEqual(result, expectedQuads)
+    })
+
+    it('should stop traversing if the end of an edge has been previously seen', () => {
+      const { expectedQuads, predicates, ptr } = datasets.traverseZeroOrMoreSelfRef2()
+
+      const result = Processor.traverseMore({
+        ptrs: [ptr],
+        end: 'object',
+        start: 'subject',
+        subjects: [null],
+        predicates,
+        objects: [null],
+        graphs: [null]
+      })
+
+      grapoiEqual(result, expectedQuads)
+    })
   })
 
   describe('.traverseOne', () => {

test/support/datasets.single.js

@@ -592,6 +592,36 @@ single.traverseZeroOrMore = () => {
   return { ...others, dataset, edges, expectedQuads }
 }
 
+single.traverseZeroOrMoreSelfRef = () => {
+  const { dataset, edges, ...others } = createPathDataset([
+    [ns.ex.start, ns.ex.propertyA, ns.ex.end],
+    [ns.ex.end, ns.ex.propertyB, ns.ex.end]
+  ])
+
+  const expectedQuads = [
+    new Path({ dataset, term: edges[0].startTerm }),
+    new Path({ edges: [edges[0]] })
+  ]
+
+  return { ...others, dataset, edges, expectedQuads }
+}
+
+single.traverseZeroOrMoreSelfRef2 = () => {
+  const { dataset, edges, ...others } = createPathDataset([
+    [ns.ex.start, ns.ex.propertyA, ns.ex.end1],
+    [ns.ex.end1, ns.ex.propertyB, ns.ex.end2],
+    [ns.ex.end2, ns.ex.propertyB, ns.ex.start]
+  ])
+
+  const expectedQuads = [
+    new Path({ dataset, term: edges[0].startTerm }),
+    new Path({ edges: [edges[0]] }),
+    new Path({ edges: [edges[0], edges[1]] })
+  ]
+
+  return { ...others, dataset, edges, expectedQuads }
+}
+
 single.traverseZeroOrOne = () => {
   const { dataset, edges, ...others } = createPathDataset([
     [ns.ex.start, ns.ex.propertyA, ns.ex.end1],