Ensure suggested questions parser returns typed sequence (#27104)

Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>

api/core/llm_generator/llm_generator.py

@@ -100,7 +100,7 @@ class LLMGenerator:
         return name
 
     @classmethod
-    def generate_suggested_questions_after_answer(cls, tenant_id: str, histories: str):
+    def generate_suggested_questions_after_answer(cls, tenant_id: str, histories: str) -> Sequence[str]:
         output_parser = SuggestedQuestionsAfterAnswerOutputParser()
         format_instructions = output_parser.get_format_instructions()
 
@@ -119,6 +119,8 @@ class LLMGenerator:
 
         prompt_messages = [UserPromptMessage(content=prompt)]
 
+        questions: Sequence[str] = []
+
         try:
             response: LLMResult = model_instance.invoke_llm(
                 prompt_messages=list(prompt_messages),

api/core/llm_generator/output_parser/suggested_questions_after_answer.py

@@ -1,17 +1,26 @@
 import json
+import logging
 import re
+from collections.abc import Sequence
 
 from core.llm_generator.prompts import SUGGESTED_QUESTIONS_AFTER_ANSWER_INSTRUCTION_PROMPT
 
+logger = logging.getLogger(__name__)
+
 
 class SuggestedQuestionsAfterAnswerOutputParser:
     def get_format_instructions(self) -> str:
         return SUGGESTED_QUESTIONS_AFTER_ANSWER_INSTRUCTION_PROMPT
 
-    def parse(self, text: str):
+    def parse(self, text: str) -> Sequence[str]:
         action_match = re.search(r"\[.*?\]", text.strip(), re.DOTALL)
+        questions: list[str] = []
         if action_match is not None:
-            json_obj = json.loads(action_match.group(0).strip())
-        else:
-            json_obj = []
-        return json_obj
+            try:
+                json_obj = json.loads(action_match.group(0).strip())
+            except json.JSONDecodeError as exc:
+                logger.warning("Failed to decode suggested questions payload: %s", exc)
+            else:
+                if isinstance(json_obj, list):
+                    questions = [question for question in json_obj if isinstance(question, str)]
+        return questions

api/services/message_service.py

@@ -288,9 +288,10 @@ class MessageService:
         )
 
         with measure_time() as timer:
-            questions: list[str] = LLMGenerator.generate_suggested_questions_after_answer(
+            questions_sequence = LLMGenerator.generate_suggested_questions_after_answer(
                 tenant_id=app_model.tenant_id, histories=histories
             )
+            questions: list[str] = list(questions_sequence)
 
         # get tracing instance
         trace_manager = TraceQueueManager(app_id=app_model.id)