[BugFix] Fix handling of stop strings and stop token ids (#3672)

tests/engine/test_stop_reason.py

@@ -0,0 +1,59 @@
+"""Test the different finish_reason="stop" situations during generation:
+    1. One of the provided stop strings
+    2. One of the provided stop tokens
+    3. The EOS token
+
+Run `pytest tests/engine/test_stop_reason.py`.
+"""
+
+import pytest
+import transformers
+
+from vllm import SamplingParams
+
+MODEL = "facebook/opt-350m"
+STOP_STR = "."
+SEED = 42
+MAX_TOKENS = 1024
+
+
+@pytest.fixture
+def vllm_model(vllm_runner):
+    vllm_model = vllm_runner(MODEL)
+    yield vllm_model
+    del vllm_model
+
+
+def test_stop_reason(vllm_model, example_prompts):
+    tokenizer = transformers.AutoTokenizer.from_pretrained(MODEL)
+    stop_token_id = tokenizer.convert_tokens_to_ids(STOP_STR)
+    llm = vllm_model.model
+
+    # test stop token
+    outputs = llm.generate(example_prompts,
+                           sampling_params=SamplingParams(
+                               seed=SEED,
+                               max_tokens=MAX_TOKENS,
+                               stop_token_ids=[stop_token_id]))
+    for output in outputs:
+        output = output.outputs[0]
+        assert output.finish_reason == "stop"
+        assert output.stop_reason == stop_token_id
+
+    # test stop string
+    outputs = llm.generate(example_prompts,
+                           sampling_params=SamplingParams(
+                               seed=SEED, max_tokens=MAX_TOKENS, stop="."))
+    for output in outputs:
+        output = output.outputs[0]
+        assert output.finish_reason == "stop"
+        assert output.stop_reason == STOP_STR
+
+    # test EOS token
+    outputs = llm.generate(example_prompts,
+                           sampling_params=SamplingParams(
+                               seed=SEED, max_tokens=MAX_TOKENS))
+    for output in outputs:
+        output = output.outputs[0]
+        assert output.finish_reason == "length" or (
+            output.finish_reason == "stop" and output.stop_reason is None)

tests/engine/test_stop_strings.py

@@ -0,0 +1,111 @@
+from typing import Any, List, Optional
+
+import pytest
+
+from vllm import CompletionOutput, LLMEngine, SamplingParams
+
+MODEL = "meta-llama/llama-2-7b-hf"
+MAX_TOKENS = 200
+
+
+@pytest.fixture(scope="session")
+def vllm_model(vllm_runner):
+    return vllm_runner(MODEL)
+
+
+@pytest.mark.skip_global_cleanup
+def test_stop_basic(vllm_model):
+    _test_stopping(vllm_model.model.llm_engine,
+                   stop=["."],
+                   include_in_output=False,
+                   expected_output="VLLM is a 100% volunteer organization",
+                   expected_reason=".")
+
+    _test_stopping(vllm_model.model.llm_engine,
+                   stop=["."],
+                   include_in_output=True,
+                   expected_output="VLLM is a 100% volunteer organization.",
+                   expected_reason=".")
+
+
+@pytest.mark.skip_global_cleanup
+def test_stop_multi_tokens(vllm_model):
+    _test_stopping(
+        vllm_model.model.llm_engine,
+        stop=["group of peo", "short"],
+        include_in_output=False,
+        expected_output="VLLM is a 100% volunteer organization. We are a ",
+        expected_reason="group of peo")
+
+    _test_stopping(
+        vllm_model.model.llm_engine,
+        stop=["group of peo", "short"],
+        include_in_output=True,
+        expected_output=
+        "VLLM is a 100% volunteer organization. We are a group of peo",
+        expected_reason="group of peo")
+
+
+@pytest.mark.skip_global_cleanup
+def test_stop_partial_token(vllm_model):
+    _test_stopping(vllm_model.model.llm_engine,
+                   stop=["gani"],
+                   include_in_output=False,
+                   expected_output="VLLM is a 100% volunteer or",
+                   expected_reason="gani")
+
+    _test_stopping(vllm_model.model.llm_engine,
+                   stop=["gani"],
+                   include_in_output=True,
+                   expected_output="VLLM is a 100% volunteer organi",
+                   expected_reason="gani")
+
+
+@pytest.mark.skip_global_cleanup
+def test_stop_token_id(vllm_model):
+    # token id 13013 => " organization"
+
+    _test_stopping(vllm_model.model.llm_engine,
+                   stop_token_ids=[13013],
+                   include_in_output=False,
+                   expected_output="VLLM is a 100% volunteer",
+                   expected_reason=13013)
+
+    _test_stopping(vllm_model.model.llm_engine,
+                   stop_token_ids=[13013],
+                   include_in_output=True,
+                   expected_output="VLLM is a 100% volunteer organization",
+                   expected_reason=13013)
+
+
+def _test_stopping(llm_engine: LLMEngine,
+                   expected_output: str,
+                   expected_reason: Any,
+                   stop: Optional[List[str]] = None,
+                   stop_token_ids: Optional[List[int]] = None,
+                   include_in_output: bool = False) -> None:
+    llm_engine.add_request(
+        "id", "A story about vLLM:\n",
+        SamplingParams(
+            temperature=0.0,
+            max_tokens=MAX_TOKENS,
+            stop=stop,
+            stop_token_ids=stop_token_ids,
+            include_stop_str_in_output=include_in_output,
+        ), None)
+
+    output: Optional[CompletionOutput] = None
+    output_text = ""
+    stop_reason = None
+    while llm_engine.has_unfinished_requests():
+        (request_output, ) = llm_engine.step()
+        (output, ) = request_output.outputs
+
+        # Ensure we don't backtrack
+        assert output.text.startswith(output_text)
+        output_text = output.text
+        stop_reason = output.stop_reason
+
+    assert output is not None
+    assert output_text == expected_output
+    assert stop_reason == expected_reason