Chain parsing lm output with original lm output even when MappingError is encountered during parsing.

langfun/core/structured/parsing.py

@@ -270,24 +270,31 @@ def call(
   if schema in (str, None):
     return lm_output if returns_message else lm_output.text
 
+  def _chain_nl_output_message(parsing_message: lf.Message):
+    """Chain the source of the parsed output to the LM output."""
+    parsing_message.root.source = lm_output
+    parsing_message.tag('parsing-lm-output')
+    parsing_message.lm_input.tag('parsing-lm-input')
+
   # Call `parsing_lm` for structured parsing.
-  parsing_message = querying.query(
-      lm_output.text,
-      schema,
-      examples=parsing_examples,
-      lm=parsing_lm or lm,
-      include_context=parsing_include_context,
-      cache_seed=cache_seed,
-      autofix=autofix,
-      autofix_lm=autofix_lm or lm,
-      protocol=protocol,
-      returns_message=True,
-      **kwargs,
-  )
-  # Chain the source of the parsed output to the LM output.
-  parsing_message.root.source = lm_output
-  parsing_message.tag('parsing-lm-output')
-  parsing_message.lm_input.tag('parsing-lm-input')
+  try:
+    parsing_message = querying.query(
+        lm_output.text,
+        schema,
+        examples=parsing_examples,
+        lm=parsing_lm or lm,
+        include_context=parsing_include_context,
+        cache_seed=cache_seed,
+        autofix=autofix,
+        autofix_lm=autofix_lm or lm,
+        protocol=protocol,
+        returns_message=True,
+        **kwargs,
+    )
+    _chain_nl_output_message(parsing_message)
+  except mapping.MappingError as e:
+    _chain_nl_output_message(e.lm_response)
+    raise e
   return parsing_message if returns_message else parsing_message.result
 
 

langfun/core/structured/parsing_test.py

@@ -686,6 +686,31 @@ def test_call_with_parsing_message_chaining(self):
         ],
         returns_message=True,
     )
+    self.assertIn('parsing-lm-output', output.tags)
+    self.assertIn('parsing-lm-input', output.source.tags)
+    self.assertEqual(output.root.text, 'Compute 1 + 2')
+
+  def test_call_with_parsing_message_chaining_on_parsing_error(self):
+    try:
+      output = parsing.call(
+          'Compute 1 + 2',
+          int,
+          lm=fake.StaticSequence(['three']),
+          parsing_lm=fake.StaticSequence(['abc']),
+          parsing_examples=[
+              mapping.MappingExample(
+                  context='Multiple four and five',
+                  input='twenty',
+                  schema=int,
+                  output=20,
+              )
+          ],
+          returns_message=True,
+      )
+    except mapping.MappingError as e:
+      output = e.lm_response
+    self.assertIn('parsing-lm-output', output.tags)
+    self.assertIn('parsing-lm-input', output.source.tags)
     self.assertEqual(output.root.text, 'Compute 1 + 2')
 
   def test_call_with_autofix(self):