Fixes variable scope for filters inside (NOT) EXIST clauses in SPARQL

Fixes #615
Also adds unit tests.

8 files changed, 98 insertions, 1 deletions

diff --git a/rdflib/plugins/sparql/algebra.py b/rdflib/plugins/sparql/algebra.py
index 099594a3..4f24740f 100644
--- a/rdflib/plugins/sparql/algebra.py
+++ b/rdflib/plugins/sparql/algebra.py
@@ -203,6 +203,9 @@ def translateExists(e):
         if isinstance(n, CompValue):
             if n.name in ('Builtin_EXISTS', 'Builtin_NOTEXISTS'):
                 n.graph = translateGroupGraphPattern(n.graph)
+                if n.graph.name == 'Filter':
+                    # filters inside (NOT) EXISTS can see vars bound outside
+                    n.graph.no_isolated_scope = True
 
     e = traverse(e, visitPost=_c)
 
diff --git a/rdflib/plugins/sparql/evaluate.py b/rdflib/plugins/sparql/evaluate.py
index e6590a25..aab3ca61 100644
--- a/rdflib/plugins/sparql/evaluate.py
+++ b/rdflib/plugins/sparql/evaluate.py
@@ -152,7 +152,7 @@ def evalLeftJoin(ctx, join):
 def evalFilter(ctx, part):
     # TODO: Deal with dict returned from evalPart!
     for c in evalPart(ctx, part.p):
-        if _ebv(part.expr, c.forget(ctx)):
+        if _ebv(part.expr, c.forget(ctx) if not part.no_isolated_scope else c):
             yield c
 
 
diff --git a/test/DAWG/rdflib/manifest.ttl b/test/DAWG/rdflib/manifest.ttl
index 63b884ad..732c594f 100644
--- a/test/DAWG/rdflib/manifest.ttl
+++ b/test/DAWG/rdflib/manifest.ttl
@@ -14,6 +14,8 @@
 	:unicode
 	:nestedbnode
     :whitespacedot
+    :minusfilter
+    :notexistsfilter
 	) .
 
 
@@ -53,3 +55,29 @@
     dawgt:approvedBy <http://gromgull.net/me> ;
     mf:action <whitespacedot.rq>
     .
+
+
+
+:minusfilter rdf:type mf:QueryEvaluationTest ;
+    mf:name "Filter in MINUS";
+    rdfs:comment """' with MINUS, the FILTER inside the pattern does not have a value for ?n and it is always unbound:'
+From https://github.com/RDFLib/rdflib/issues/615, contributed by https://github.com/pfps""" ;
+    dawgt:approval dawgt:Approved ;
+    dawgt:approvedBy <http://gromgull.net/me> ;
+    mf:action
+         [ qt:query  <minusfilter.rq> ;
+           qt:data <minusfilter.ttl> ] ;
+    mf:result  <minusfilter.srx>
+    .
+
+:notexistsfilter rdf:type mf:QueryEvaluationTest ;
+    mf:name "Filter in NOT EXISTS";
+    rdfs:comment """'the FILTER inside the NOT EXISTS has access to the value of ?n for the solution being considered.'
+From https://github.com/RDFLib/rdflib/issues/615, contributed by https://github.com/pfps""" ;
+    dawgt:approval dawgt:Approved ;
+    dawgt:approvedBy <http://gromgull.net/me> ;
+    mf:action
+         [ qt:query  <notexistsfilter.rq> ;
+           qt:data <minusfilter.ttl> ] ;
+    mf:result  <notexistsfilter.srx>
+    .
diff --git a/test/DAWG/rdflib/minusfilter.rq b/test/DAWG/rdflib/minusfilter.rq
new file mode 100644
index 00000000..b381afe6
--- /dev/null
+++ b/test/DAWG/rdflib/minusfilter.rq
@@ -0,0 +1,8 @@
+PREFIX : <http://example.com/>
+SELECT ?x ?n WHERE {
+    ?x :p ?n
+    MINUS {
+        ?x :q ?m .
+        FILTER(?n = ?m)
+    }
+}
diff --git a/test/DAWG/rdflib/minusfilter.srx b/test/DAWG/rdflib/minusfilter.srx
new file mode 100644
index 00000000..94baded6
--- /dev/null
+++ b/test/DAWG/rdflib/minusfilter.srx
@@ -0,0 +1,25 @@
+<?xml version="1.0"?>
+<sparql xmlns="http://www.w3.org/2005/sparql-results#">
+  <head>
+	<variable name="x"/>
+	<variable name="n"/>
+  </head>
+  <results>
+    <result>
+      <binding name="x">
+        <uri>http://example.com/a</uri>
+      </binding>
+      <binding name="n">
+        <literal datatype="http://www.w3.org/2001/XMLSchema#integer">1</literal>
+      </binding>
+    </result>
+    <result>
+      <binding name="x">
+        <uri>http://example.com/b</uri>
+      </binding>
+      <binding name="n">
+        <literal datatype="http://www.w3.org/2001/XMLSchema#decimal">3.0</literal>
+      </binding>
+    </result>
+  </results>
+</sparql>
diff --git a/test/DAWG/rdflib/minusfilter.ttl b/test/DAWG/rdflib/minusfilter.ttl
new file mode 100644
index 00000000..a4ec1d64
--- /dev/null
+++ b/test/DAWG/rdflib/minusfilter.ttl
@@ -0,0 +1,8 @@
+@prefix : <http://example.com/> .
+:a :p 1 .
+:a :q 1 .
+:a :q 2 .
+
+:b :p 3.0 .
+:b :q 4.0 .
+:b :q 5.0 .
\ No newline at end of file
diff --git a/test/DAWG/rdflib/notexistsfilter.rq b/test/DAWG/rdflib/notexistsfilter.rq
new file mode 100644
index 00000000..586be72a
--- /dev/null
+++ b/test/DAWG/rdflib/notexistsfilter.rq
@@ -0,0 +1,8 @@
+PREFIX : <http://example.com/>
+SELECT ?x ?n WHERE {
+    ?x :p ?n
+    FILTER NOT EXISTS {
+        ?x :q ?m .
+        FILTER(?n = ?m)
+    }
+}
diff --git a/test/DAWG/rdflib/notexistsfilter.srx b/test/DAWG/rdflib/notexistsfilter.srx
new file mode 100644
index 00000000..fede17eb
--- /dev/null
+++ b/test/DAWG/rdflib/notexistsfilter.srx
@@ -0,0 +1,17 @@
+<?xml version="1.0"?>
+<sparql xmlns="http://www.w3.org/2005/sparql-results#">
+  <head>
+	<variable name="x"/>
+	<variable name="n"/>
+  </head>
+  <results>
+    <result>
+      <binding name="x">
+        <uri>http://example.com/b</uri>
+      </binding>
+      <binding name="n">
+        <literal datatype="http://www.w3.org/2001/XMLSchema#decimal">3.0</literal>
+      </binding>
+    </result>
+  </results>
+</sparql>