Fix incorrect deskolemization of literals

rdflib/graph.py

@@ -2034,10 +2034,11 @@ def do_de_skolemize2(t: _TripleType) -> _TripleType:
             elif Genid._is_external_skolem(s):
                 s = Genid(s).de_skolemize()
 
-            if RDFLibGenid._is_rdflib_skolem(o):
-                o = RDFLibGenid(o).de_skolemize()
-            elif Genid._is_external_skolem(o):
-                o = Genid(o).de_skolemize()
+            if isinstance(o, URIRef):
+                if RDFLibGenid._is_rdflib_skolem(o):
+                    o = RDFLibGenid(o).de_skolemize()
+                elif Genid._is_external_skolem(o):
+                    o = Genid(o).de_skolemize()
 
             return s, p, o
 

test/test_issues/test_issue3126.py

@@ -0,0 +1,21 @@
+import pytest
+
+from rdflib import Graph
+
+
+def test_skolem_de_skolem_roundtrip():
+    """Test deskolemization should ignore literals.
+
+    Issue: https://github.com/RDFLib/rdflib/issues/3126
+    """
+
+    nt = (
+        '<http://example.com> <http://example.com> "http://example.com [some remark]" .'
+    )
+
+    graph = Graph().parse(data=nt, format="nt").de_skolemize()
+
+    try:
+        graph.de_skolemize()
+    except BaseException as ex:
+        pytest.fail(f"Unexpected error: {ex}")