Add log message on unparsable JSON (#28)

* add json parse failures to log

* log json parsing errors

python/graphrag/graphrag/llm/openai/json_parsing_llm.py

@@ -3,6 +3,7 @@
 """An LLM that unpacks cached JSON responses."""
 
 import json
+import logging
 from typing import cast
 
 from typing_extensions import Unpack
@@ -16,6 +17,10 @@
     LLMOutput,
 )
 
+log = logging.getLogger(__name__)
+
+UNPARSABLE_JSON = "Failed to parse JSON data"
+
 
 class JsonParsingLLM(LLM[CompletionInput, CompletionOutput]):
     """An OpenAI History-Tracking LLM."""
@@ -33,5 +38,9 @@ async def __call__(
         """Call the LLM with the input and kwargs."""
         result = await self._delegate(input, **kwargs)
         if kwargs.get("json") and result.json is None and result.output is not None:
-            result.json = cast(dict, json.loads(result.output))
+            try:
+                result.json = cast(dict, json.loads(result.output))
+            except json.JSONDecodeError as e:
+                log.error("Failed to parse JSON output:\n%s", result.output)  # noqa TRY400
+                raise ValueError(UNPARSABLE_JSON) from e
         return result