[Bugfix] Log platform plugin detection failures (#52285)

Signed-off-by: Luyi Xiao <xiao.luy@northeastern.edu>
Co-authored-by: OpenAI Codex <codex@openai.com>

tests/test_zen_cpu_platform_detection.py

@@ -1,10 +1,16 @@
 # SPDX-License-Identifier: Apache-2.0
 # SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+import builtins
+import logging
 from unittest.mock import mock_open, patch
 
 import pytest
 
-from vllm.platforms import _is_amd_zen_cpu, resolve_current_platform_cls_qualname
+from vllm.platforms import (
+    _is_amd_zen_cpu,
+    cpu_platform_plugin,
+    resolve_current_platform_cls_qualname,
+)
 
 
 def test_is_amd_zen_cpu_detects_amd_with_avx512():
@@ -57,3 +63,31 @@ def test_cpu_target_selects_cpu_platform_from_non_cpu_wheel(
     # suffix or host accelerators (a native CI job can reuse a ROCm wheel).
     version_matches.assert_not_called()
     rocm_plugin.assert_not_called()
+
+
+def test_platform_detection_logs_zentorch_import_failure(caplog):
+    original_import = builtins.__import__
+
+    def import_with_broken_zentorch(name, *args, **kwargs):
+        if name == "zentorch":
+            raise OSError("incompatible shared library")
+        return original_import(name, *args, **kwargs)
+
+    with (
+        patch("vllm.platforms.envs.VLLM_TARGET_DEVICE", "cuda"),
+        patch.dict(
+            "vllm.platforms.builtin_platform_plugins",
+            {"cpu": cpu_platform_plugin},
+            clear=True,
+        ),
+        patch("vllm.platforms.load_plugins_by_group", return_value={}),
+        patch("vllm.platforms.vllm_version_matches_substr", return_value=True),
+        patch("vllm.platforms._is_amd_zen_cpu", return_value=True),
+        patch.object(builtins, "__import__", side_effect=import_with_broken_zentorch),
+        caplog.at_level(logging.DEBUG, logger="vllm.platforms"),
+    ):
+        platform = resolve_current_platform_cls_qualname()
+
+    assert platform == "vllm.platforms.interface.UnspecifiedPlatform"
+    assert "Platform plugin cpu failed during detection" in caplog.text
+    assert "OSError: incompatible shared library" in caplog.text

vllm/platforms/__init__.py

@@ -251,7 +251,11 @@ def resolve_current_platform_cls_qualname() -> str:
             if platform_cls_qualname is not None:
                 activated_plugins.append(name)
         except Exception:
-            pass
+            logger.debug(
+                "Platform plugin %s failed during detection.",
+                name,
+                exc_info=True,
+            )
 
     activated_builtin_plugins = list(
         set(activated_plugins) & set(builtin_platform_plugins.keys())