Fix #26037: Skip CUDA platform detection when displaying help

tests/entrypoints/test_cli_main.py

@@ -0,0 +1,66 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+"""Tests for the CLI main entrypoint to ensure help doesn't trigger
+platform detection.
+"""
+
+import sys
+from unittest.mock import patch
+
+import pytest
+
+
+@pytest.mark.parametrize(
+    "argv",
+    [
+        ["vllm", "--help"],
+        ["vllm", "serve", "--help"],
+        ["vllm", "-h"],
+        ["vllm", "bench", "--help"],
+        ["vllm", "serve", "--help=ModelConfig"],
+    ],
+)
+def test_needs_help_detects_help_flags(argv):
+    """Test that needs_help() correctly detects help flags in sys.argv."""
+    from vllm.engine.arg_utils import needs_help
+
+    # patch.object on sys.argv is safe — it's a simple list attribute
+    # with no lazy-init or side-effect machinery.
+    with patch.object(sys, "argv", argv):
+        assert needs_help(), f"needs_help() should return True for {argv}"
+
+
+@pytest.mark.parametrize(
+    "argv",
+    [
+        ["vllm", "serve", "--model", "test"],
+        ["vllm", "bench", "latency", "--model", "test"],
+        ["vllm", "collect-env"],
+    ],
+)
+def test_needs_help_returns_false_without_help_flags(argv):
+    """Test that needs_help() returns False when no help flag is present."""
+    from vllm.engine.arg_utils import needs_help
+
+    with patch.object(sys, "argv", argv):
+        assert not needs_help(), f"needs_help() should return False for {argv}"
+
+
+def test_bench_help_skips_platform_detection():
+    """Test that the bench guard in main() is skipped when --help is present.
+
+    The guard in main.py is:
+        if sys.argv[1] == "bench" and not showing_help
+    When showing_help is True, current_platform is never accessed for
+    the bench CPU-override, avoiding unnecessary platform detection.
+    """
+    from vllm.engine.arg_utils import needs_help
+
+    # Verify the guard: needs_help() == True means "not showing_help" is False,
+    # so the bench platform-override block is skipped.
+    with patch.object(sys, "argv", ["vllm", "bench", "--help"]):
+        assert needs_help(), "needs_help() should be True for bench --help"
+
+    # Without --help the guard would be entered
+    with patch.object(sys, "argv", ["vllm", "bench", "latency"]):
+        assert not needs_help(), "needs_help() should be False without --help"

tests/entrypoints/test_utils_lazy_import.py

@@ -0,0 +1,33 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+"""Test that get_max_tokens lazily imports current_platform
+rather than relying on a module-level import."""
+
+import subprocess
+import sys
+
+
+def test_get_max_tokens_lazy_platform_import():
+    """current_platform should not be imported at module level in utils.py."""
+    result = subprocess.run(
+        [
+            sys.executable,
+            "-c",
+            (
+                "import ast, inspect, textwrap; "
+                "from vllm.entrypoints import utils; "
+                "src = inspect.getsource(utils.get_max_tokens); "
+                "tree = ast.parse(textwrap.dedent(src)); "
+                "imports = [n for n in ast.walk(tree) "
+                "  if isinstance(n, ast.ImportFrom) "
+                "  and n.module == 'vllm.platforms']; "
+                "assert imports, 'get_max_tokens should have a local platform import'"
+            ),
+        ],
+        capture_output=True,
+        text=True,
+    )
+    assert result.returncode == 0, (
+        f"Subprocess failed (rc={result.returncode}):\n"
+        f"stdout: {result.stdout}\nstderr: {result.stderr}"
+    )

vllm/engine/arg_utils.py

@@ -241,11 +241,18 @@ def get_type_hints(type_hint: TypeHint) -> set[TypeHint]:
     return type_hints
 
 
-NEEDS_HELP = (
-    any("--help" in arg for arg in sys.argv)  # vllm SUBCOMMAND --help
-    or (argv0 := sys.argv[0]).endswith("mkdocs")  # mkdocs SUBCOMMAND
-    or argv0.endswith("mkdocs/__main__.py")  # python -m mkdocs SUBCOMMAND
-)
+def needs_help() -> bool:
+    """Check if help is being requested via CLI flags or mkdocs."""
+    return (
+        any(
+            arg == "-h" or arg.startswith("--help") for arg in sys.argv
+        )  # vllm SUBCOMMAND --help/-h/--help=X
+        or (argv0 := sys.argv[0]).endswith("mkdocs")  # mkdocs SUBCOMMAND
+        or argv0.endswith("mkdocs/__main__.py")  # python -m mkdocs SUBCOMMAND
+    )
+
+
+NEEDS_HELP = needs_help()
 
 
 def _maybe_add_docs_url(cls: Any) -> str:
@@ -2412,7 +2419,8 @@ def add_cli_args(
             "- DEBUG: Prompt inputs (e.g: text, token IDs).\n"
             "You can set the minimum log level via `VLLM_LOGGING_LEVEL`.",
         )
-        current_platform.pre_register_and_update(parser)
+        if not NEEDS_HELP:
+            current_platform.pre_register_and_update(parser)
         return parser
 
 

vllm/entrypoints/cli/main.py

@@ -8,6 +8,7 @@
 import importlib.metadata
 import sys
 
+from vllm.engine.arg_utils import needs_help
 from vllm.logger import init_logger
 
 logger = init_logger(__name__)
@@ -34,8 +35,9 @@ def main():
 
     cli_env_setup()
 
-    # For 'vllm bench *': use CPU instead of UnspecifiedPlatform by default
-    if len(sys.argv) > 1 and sys.argv[1] == "bench":
+    # For 'vllm bench *': use CPU instead of UnspecifiedPlatform by default.
+    # When showing help, skip this to avoid triggering platform detection.
+    if len(sys.argv) > 1 and sys.argv[1] == "bench" and not needs_help():
         logger.debug(
             "Bench command detected, must ensure current platform is not "
             "UnspecifiedPlatform to avoid device type inference error"

vllm/entrypoints/utils.py

@@ -25,7 +25,6 @@
 )
 from vllm.entrypoints.openai.models.protocol import LoRAModulePath
 from vllm.logger import current_formatter_type, init_logger
-from vllm.platforms import current_platform
 from vllm.utils.argparse_utils import FlexibleArgumentParser
 
 logger = init_logger(__name__)
@@ -178,6 +177,8 @@ def get_max_tokens(
     default_sampling_params: dict,
     override_max_tokens: int | None = None,
 ) -> int:
+    from vllm.platforms import current_platform
+
     if max_model_len < input_length:
         raise ValueError(
             f"Input length ({input_length}) exceeds model's maximum "