Ensure that the Google GenAI SDK instrumentation correctly populates "finish_reasons" on the span. (#3417)

* Fix bug where 'gen_ai.response.finish_reasons' was not being correctly populated.

* Update changelog.

* Reformat with ruff.

instrumentation-genai/opentelemetry-instrumentation-google-genai/CHANGELOG.md

@@ -9,6 +9,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Restructure tests to keep in line with repository conventions ([#3344](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/3344))
 
+- Fix [bug](https://github.com/open-telemetry/opentelemetry-python-contrib/issues/3416) where
+span attribute `gen_ai.response.finish_reasons` is empty ([#3417](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/3417))
+
 ## Version 0.1b0 (2025-03-05)
 
 - Add support for async and streaming.

instrumentation-genai/opentelemetry-instrumentation-google-genai/src/opentelemetry/instrumentation/google_genai/generate_content.py

@@ -252,6 +252,7 @@ class _GenerateContentInstrumentationHelper:
         # need to be reflected back into the span attributes.
         #
         # See also: TODOS.md.
+        self._update_finish_reasons(response)
         self._maybe_update_token_counts(response)
         self._maybe_update_error_type(response)
         self._maybe_log_response(response)
@@ -275,6 +276,18 @@ class _GenerateContentInstrumentationHelper:
         self._record_token_usage_metric()
         self._record_duration_metric()
 
+    def _update_finish_reasons(self, response):
+        if not response.candidates:
+            return
+        for candidate in response.candidates:
+            finish_reason = candidate.finish_reason
+            if finish_reason is None:
+                continue
+            finish_reason_str = finish_reason.name.lower().removeprefix(
+                "finish_reason_"
+            )
+            self._finish_reasons_set.add(finish_reason_str)
+
     def _maybe_update_token_counts(self, response: GenerateContentResponse):
         input_tokens = _get_response_property(
             response, "usage_metadata.prompt_token_count"

instrumentation-genai/opentelemetry-instrumentation-google-genai/tests/generate_content/test_finish_reasons.py

@@ -0,0 +1,143 @@
+# Copyright The OpenTelemetry Authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+
+from google.genai import types as genai_types
+
+from .base import TestCase
+
+
+class FinishReasonsTestCase(TestCase):
+    def generate_and_get_span_finish_reasons(self):
+        self.client.models.generate_content(
+            model="gemini-2.5-flash-001", contents="Some prompt"
+        )
+        span = self.otel.get_span_named(
+            "generate_content gemini-2.5-flash-001"
+        )
+        assert span is not None
+        assert "gen_ai.response.finish_reasons" in span.attributes
+        return list(span.attributes["gen_ai.response.finish_reasons"])
+
+    def test_single_candidate_with_valid_reason(self):
+        self.configure_valid_response(
+            candidate=genai_types.Candidate(
+                finish_reason=genai_types.FinishReason.STOP
+            )
+        )
+        self.assertEqual(self.generate_and_get_span_finish_reasons(), ["stop"])
+
+    def test_single_candidate_with_safety_reason(self):
+        self.configure_valid_response(
+            candidate=genai_types.Candidate(
+                finish_reason=genai_types.FinishReason.SAFETY
+            )
+        )
+        self.assertEqual(
+            self.generate_and_get_span_finish_reasons(), ["safety"]
+        )
+
+    def test_single_candidate_with_max_tokens_reason(self):
+        self.configure_valid_response(
+            candidate=genai_types.Candidate(
+                finish_reason=genai_types.FinishReason.MAX_TOKENS
+            )
+        )
+        self.assertEqual(
+            self.generate_and_get_span_finish_reasons(), ["max_tokens"]
+        )
+
+    def test_single_candidate_with_no_reason(self):
+        self.configure_valid_response(
+            candidate=genai_types.Candidate(finish_reason=None)
+        )
+        self.assertEqual(self.generate_and_get_span_finish_reasons(), [])
+
+    def test_single_candidate_with_unspecified_reason(self):
+        self.configure_valid_response(
+            candidate=genai_types.Candidate(
+                finish_reason=genai_types.FinishReason.FINISH_REASON_UNSPECIFIED
+            )
+        )
+        self.assertEqual(
+            self.generate_and_get_span_finish_reasons(), ["unspecified"]
+        )
+
+    def test_multiple_candidates_with_valid_reasons(self):
+        self.configure_valid_response(
+            candidates=[
+                genai_types.Candidate(
+                    finish_reason=genai_types.FinishReason.MAX_TOKENS
+                ),
+                genai_types.Candidate(
+                    finish_reason=genai_types.FinishReason.STOP
+                ),
+            ]
+        )
+        self.assertEqual(
+            self.generate_and_get_span_finish_reasons(), ["max_tokens", "stop"]
+        )
+
+    def test_sorts_finish_reasons(self):
+        self.configure_valid_response(
+            candidates=[
+                genai_types.Candidate(
+                    finish_reason=genai_types.FinishReason.STOP
+                ),
+                genai_types.Candidate(
+                    finish_reason=genai_types.FinishReason.MAX_TOKENS
+                ),
+                genai_types.Candidate(
+                    finish_reason=genai_types.FinishReason.SAFETY
+                ),
+            ]
+        )
+        self.assertEqual(
+            self.generate_and_get_span_finish_reasons(),
+            ["max_tokens", "safety", "stop"],
+        )
+
+    def test_deduplicates_finish_reasons(self):
+        self.configure_valid_response(
+            candidates=[
+                genai_types.Candidate(
+                    finish_reason=genai_types.FinishReason.STOP
+                ),
+                genai_types.Candidate(
+                    finish_reason=genai_types.FinishReason.MAX_TOKENS
+                ),
+                genai_types.Candidate(
+                    finish_reason=genai_types.FinishReason.STOP
+                ),
+                genai_types.Candidate(
+                    finish_reason=genai_types.FinishReason.STOP
+                ),
+                genai_types.Candidate(
+                    finish_reason=genai_types.FinishReason.SAFETY
+                ),
+                genai_types.Candidate(
+                    finish_reason=genai_types.FinishReason.STOP
+                ),
+                genai_types.Candidate(
+                    finish_reason=genai_types.FinishReason.STOP
+                ),
+                genai_types.Candidate(
+                    finish_reason=genai_types.FinishReason.STOP
+                ),
+            ]
+        )
+        self.assertEqual(
+            self.generate_and_get_span_finish_reasons(),
+            ["max_tokens", "safety", "stop"],
+        )