[V1][Metrics][Plugin] Add plugin support for custom StatLoggerBase implementations (#22456)

Signed-off-by: tovam <tovam@pliops.com>

tests/plugins/vllm_add_dummy_stat_logger/dummy_stat_logger/dummy_stat_logger.py

@@ -0,0 +1,29 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+
+from vllm.v1.metrics.loggers import StatLoggerBase
+
+
+class DummyStatLogger(StatLoggerBase):
+    """
+    A dummy stat logger for testing purposes.
+    Implements the minimal interface expected by StatLoggerManager.
+    """
+
+    def __init__(self, vllm_config, engine_idx=0):
+        self.vllm_config = vllm_config
+        self.engine_idx = engine_idx
+        self.recorded = []
+        self.logged = False
+        self.engine_initialized = False
+
+    def record(self, scheduler_stats, iteration_stats, mm_cache_stats, engine_idx):
+        self.recorded.append(
+            (scheduler_stats, iteration_stats, mm_cache_stats, engine_idx)
+        )
+
+    def log(self):
+        self.logged = True
+
+    def log_engine_initialized(self):
+        self.engine_initialized = True

tests/plugins/vllm_add_dummy_stat_logger/setup.py

@@ -0,0 +1,15 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+
+from setuptools import setup
+
+setup(
+    name="dummy_stat_logger",
+    version="0.1",
+    packages=["dummy_stat_logger"],
+    entry_points={
+        "vllm.stat_logger_plugins": [
+            "dummy_stat_logger = dummy_stat_logger.dummy_stat_logger:DummyStatLogger"  # noqa
+        ]
+    },
+)

tests/plugins_tests/test_stats_logger_plugins.py

@@ -0,0 +1,76 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+
+import pytest
+from dummy_stat_logger.dummy_stat_logger import DummyStatLogger
+
+from vllm.config import VllmConfig
+from vllm.engine.arg_utils import AsyncEngineArgs
+from vllm.v1.engine.async_llm import AsyncLLM
+from vllm.v1.metrics.loggers import load_stat_logger_plugin_factories
+
+
+def test_stat_logger_plugin_is_discovered(monkeypatch: pytest.MonkeyPatch):
+    with monkeypatch.context() as m:
+        m.setenv("VLLM_PLUGINS", "dummy_stat_logger")
+
+        factories = load_stat_logger_plugin_factories()
+        assert len(factories) == 1, f"Expected 1 factory, got {len(factories)}"
+        assert factories[0] is DummyStatLogger, (
+            f"Expected DummyStatLogger class, got {factories[0]}"
+        )
+
+        # instantiate and confirm the right type
+        vllm_config = VllmConfig()
+        instance = factories[0](vllm_config)
+        assert isinstance(instance, DummyStatLogger)
+
+
+def test_no_plugins_loaded_if_env_empty(monkeypatch: pytest.MonkeyPatch):
+    with monkeypatch.context() as m:
+        m.setenv("VLLM_PLUGINS", "")
+
+        factories = load_stat_logger_plugin_factories()
+        assert factories == []
+
+
+def test_invalid_stat_logger_plugin_raises(monkeypatch: pytest.MonkeyPatch):
+    def fake_plugin_loader(group: str):
+        assert group == "vllm.stat_logger_plugins"
+        return {"bad": object()}
+
+    with monkeypatch.context() as m:
+        m.setattr(
+            "vllm.v1.metrics.loggers.load_plugins_by_group",
+            fake_plugin_loader,
+        )
+        with pytest.raises(
+            TypeError,
+            match="Stat logger plugin 'bad' must be a subclass of StatLoggerBase",
+        ):
+            load_stat_logger_plugin_factories()
+
+
+@pytest.mark.asyncio
+async def test_stat_logger_plugin_integration_with_engine(
+    monkeypatch: pytest.MonkeyPatch,
+):
+    with monkeypatch.context() as m:
+        m.setenv("VLLM_PLUGINS", "dummy_stat_logger")
+
+        engine_args = AsyncEngineArgs(
+            model="facebook/opt-125m",
+            enforce_eager=True,  # reduce test time
+            disable_log_stats=True,  # disable default loggers
+        )
+
+        engine = AsyncLLM.from_engine_args(engine_args=engine_args)
+
+        assert len(engine.logger_manager.stat_loggers) == 2
+        assert len(engine.logger_manager.stat_loggers[0].per_engine_stat_loggers) == 1
+        assert isinstance(
+            engine.logger_manager.stat_loggers[0].per_engine_stat_loggers[0],
+            DummyStatLogger,
+        )
+
+        engine.shutdown()

tests/v1/metrics/test_engine_logger_apis.py

@@ -4,33 +4,13 @@ import copy
 
 import pytest
 
+from tests.plugins.vllm_add_dummy_stat_logger.dummy_stat_logger.dummy_stat_logger import (  # noqa E501
+    DummyStatLogger,
+)
 from vllm.v1.engine.async_llm import AsyncEngineArgs, AsyncLLM
 from vllm.v1.metrics.ray_wrappers import RayPrometheusStatLogger
 
 
-class DummyStatLogger:
-    """
-    A dummy stat logger for testing purposes.
-    Implements the minimal interface expected by StatLoggerManager.
-    """
-
-    def __init__(self, vllm_config, engine_idx):
-        self.vllm_config = vllm_config
-        self.engine_idx = engine_idx
-        self.recorded = []
-        self.logged = False
-        self.engine_initialized = False
-
-    def record(self, scheduler_stats, iteration_stats, engine_idx):
-        self.recorded.append((scheduler_stats, iteration_stats, engine_idx))
-
-    def log(self):
-        self.logged = True
-
-    def log_engine_initialized(self):
-        self.engine_initialized = True
-
-
 @pytest.fixture
 def log_stats_enabled_engine_args():
     """