Only run `get_attr_docs` if generating help text (#23723)

Signed-off-by: Harry Mellor <19981378+hmellor@users.noreply.github.com>

vllm/engine/arg_utils.py

@@ -152,9 +152,17 @@ def is_online_quantization(quantization: Any) -> bool:
     return quantization in ["inc"]
 
 
+NEEDS_HELP = (
+    "--help" in (argv := sys.argv)  # vllm SUBCOMMAND --help
+    or (argv0 := argv[0]).endswith("mkdocs")  # mkdocs SUBCOMMAND
+    or argv0.endswith("mkdocs/__main__.py")  # python -m mkdocs SUBCOMMAND
+)
+
+
 @functools.lru_cache(maxsize=30)
 def _compute_kwargs(cls: ConfigType) -> dict[str, Any]:
-    cls_docs = get_attr_docs(cls)
+    # Save time only getting attr docs if we're generating help text
+    cls_docs = get_attr_docs(cls) if NEEDS_HELP else {}
     kwargs = {}
     for field in fields(cls):
         # Get the set of possible types for the field
@@ -172,7 +180,7 @@ def _compute_kwargs(cls: ConfigType) -> dict[str, Any]:
 
         # Get the help text for the field
         name = field.name
-        help = cls_docs[name].strip()
+        help = cls_docs.get(name, "").strip()
         # Escape % for argparse
         help = help.replace("%", "%%")
 
@@ -254,6 +262,9 @@ def _compute_kwargs(cls: ConfigType) -> dict[str, Any]:
 def get_kwargs(cls: ConfigType) -> dict[str, Any]:
     """Return argparse kwargs for the given Config dataclass.
 
+    If `--help` or `mkdocs` are not present in the command line command, the
+    attribute documentation will not be included in the help output.
+
     The heavy computation is cached via functools.lru_cache, and a deep copy
     is returned so callers can mutate the dictionary without affecting the
     cached version.