fix: TriG parser error handling for nested graphs (#2468)

Raise an error when nested graphs occur in TriG.

With this change, the <http://www.w3.org/2013/TriGTests/#trig-graph-bad-07> test passes.

---------

Co-authored-by: WhiteGobo <richardfechner@posteo.net>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Iwan Aucamp <aucampia@gmail.com>

Author: 3 people

rdflib/plugins/parsers/trig.py

@@ -98,6 +98,9 @@ def graph(self, argstr: str, i: int) -> int:
 
         j = i + 1
 
+        if self._context is not None:
+            self.BadSyntax(argstr, i, "Nested graphs are not allowed")
+
         oldParentContext = self._parentContext
         self._parentContext = self._context
         reason2 = self._reason2

test/test_w3c_spec/test_trig_w3c.py

@@ -176,9 +176,6 @@ def check_entry(entry: ManifestEntry) -> None:
     f"{REMOTE_BASE_IRI}#trig-graph-bad-01": pytest.mark.xfail(
         reason="accepts GRAPH with no name"
     ),
-    f"{REMOTE_BASE_IRI}#trig-graph-bad-07": pytest.mark.xfail(
-        reason="accepts nested GRAPH"
-    ),
 }
 
 

test_reports/rdflib_w3c_trig-HEAD.ttl

@@ -971,7 +971,7 @@
     earl:assertedBy <https://github.com/RDFLib/rdflib> ;
     earl:mode earl:automatic ;
     earl:result [ a earl:TestResult ;
-            earl:outcome earl:failed ] ;
+            earl:outcome earl:passed ] ;
     earl:subject <https://github.com/RDFLib/rdflib> ;
     earl:test <http://www.w3.org/2013/TriGTests/#trig-graph-bad-07> .