fix: JSON-LD context construction from a dict

A variable was only being initialized for string-valued inputs, but if a `dict`
input was passed the variable would still be accessed, resulting in a
`UnboundLocalError`.

This change initializes the variable always, instead of only when string-valued
input is used to construct a JSON-LD context.

- Closes <#2303>.

rdflib/plugins/shared/jsonld/context.py

@@ -421,13 +421,13 @@ def _prep_sources(
     ):
         for source in inputs:
             source_url = in_source_url
+            new_base = base
             if isinstance(source, str):
                 source_url = source
                 source_doc_base = base or self.doc_base
                 new_ctx = self._fetch_context(
                     source, source_doc_base, referenced_contexts
                 )
-                new_base = base
                 if new_ctx is None:
                     continue
                 else:

test/jsonld/test_context.py

@@ -3,6 +3,7 @@
 """
 
 from functools import wraps
+from pathlib import Path
 from typing import Any, Dict
 
 from rdflib.plugins.shared.jsonld import context, errors
@@ -213,3 +214,23 @@ def test_invalid_remote_context():
     ctx_url = "http://example.org/recursive.jsonld"
     SOURCES[ctx_url] = {"key": "value"}
     ctx = Context(ctx_url)
+
+
+def test_file_source(tmp_path: Path) -> None:
+    """
+    A file URI source to `Context` gets processed correctly.
+    """
+    file = tmp_path / "context.jsonld"
+    file.write_text(r"""{ "@context": { "ex": "http://example.com/" } }""")
+    ctx = Context(source=file.as_uri())
+    assert "http://example.com/" == ctx.terms["ex"].id
+
+
+def test_dict_source(tmp_path: Path) -> None:
+    """
+    A dictionary source to `Context` gets processed correctly.
+    """
+    file = tmp_path / "context.jsonld"
+    file.write_text(r"""{ "@context": { "ex": "http://example.com/" } }""")
+    ctx = Context(source=[{"@context": file.as_uri()}])
+    assert "http://example.com/" == ctx.terms["ex"].id