[Docs] Reduce noise in docs and --help from the JSON tip (#22567)

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

docs/cli/README.md

@@ -16,6 +16,16 @@ Available Commands:
 vllm {chat,complete,serve,bench,collect-env,run-batch}
 ```
 
+When passing JSON CLI arguments, the following sets of arguments are equivalent:
+
+- `--json-arg '{"key1": "value1", "key2": {"key3": "value2"}}'`
+- `--json-arg.key1 value1 --json-arg.key2.key3 value2`
+
+Additionally, list elements can be passed individually using `+`:
+
+- `--json-arg '{"key4": ["value3", "value4", "value5"]}'`
+- `--json-arg.key4+ value3 --json-arg.key4+='value4,value5'`
+
 ## serve
 
 Start the vLLM OpenAI Compatible API server.

docs/configuration/engine_args.md

@@ -11,6 +11,16 @@ Engine arguments control the behavior of the vLLM engine.
 
 The engine argument classes, [EngineArgs][vllm.engine.arg_utils.EngineArgs] and [AsyncEngineArgs][vllm.engine.arg_utils.AsyncEngineArgs], are a combination of the configuration classes defined in [vllm.config][]. Therefore, if you are interested in developer documentation, we recommend looking at these configuration classes as they are the source of truth for types, defaults and docstrings.
 
+When passing JSON CLI arguments, the following sets of arguments are equivalent:
+
+- `--json-arg '{"key1": "value1", "key2": {"key3": "value2"}}'`
+- `--json-arg.key1 value1 --json-arg.key2.key3 value2`
+
+Additionally, list elements can be passed individually using `+`:
+
+- `--json-arg '{"key4": ["value3", "value4", "value5"]}'`
+- `--json-arg.key4+ value3 --json-arg.key4+='value4,value5'`
+
 ## `EngineArgs`
 
 --8<-- "docs/argparse/engine_args.md"

vllm/engine/arg_utils.py

@@ -178,17 +178,8 @@ def _compute_kwargs(cls: ConfigType) -> dict[str, Any]:
         kwargs[name] = {"default": default, "help": help}
 
         # Set other kwargs based on the type hints
-        json_tip = """Should either be a valid JSON string or JSON keys
-passed individually. For example, the following sets of arguments are
-equivalent:
-
-- `--json-arg '{"key1": "value1", "key2": {"key3": "value2"}}'`\n
-- `--json-arg.key1 value1 --json-arg.key2.key3 value2`
-
-Additionally, list elements can be passed individually using `+`:
-
-- `--json-arg '{"key4": ["value3", "value4", "value5"]}'`\n
-- `--json-arg.key4+ value3 --json-arg.key4+='value4,value5'`"""
+        json_tip = ("Should either be a valid JSON string or JSON keys passed "
+                    "individually.")
         if dataclass_cls is not None:
 
             def parse_dataclass(val: str, cls=dataclass_cls) -> Any:
@@ -1831,13 +1822,3 @@ def human_readable_int(value):
 
     # Regular plain number.
     return int(value)
-
-
-# These functions are used by sphinx to build the documentation
-def _engine_args_parser():
-    return EngineArgs.add_cli_args(FlexibleArgumentParser())
-
-
-def _async_engine_args_parser():
-    return AsyncEngineArgs.add_cli_args(FlexibleArgumentParser(),
-                                        async_args_only=True)

vllm/utils/__init__.py

@@ -1669,11 +1669,19 @@ class FlexibleArgumentParser(ArgumentParser):
     """ArgumentParser that allows both underscore and dash in names."""
 
     _deprecated: set[Action] = set()
+    _json_tip: str = (
+        "When passing JSON CLI arguments, the following sets of arguments "
+        "are equivalent:\n"
+        '   --json-arg \'{"key1": "value1", "key2": {"key3": "value2"}}\'\n'
+        "   --json-arg.key1 value1 --json-arg.key2.key3 value2\n\n"
+        "Additionally, list elements can be passed individually using +:\n"
+        '   --json-arg \'{"key4": ["value3", "value4", "value5"]}\'\n'
+        "   --json-arg.key4+ value3 --json-arg.key4+=\'value4,value5\'\n\n")
 
     def __init__(self, *args, **kwargs):
-        # Set the default 'formatter_class' to SortedHelpFormatter
-        if 'formatter_class' not in kwargs:
-            kwargs['formatter_class'] = SortedHelpFormatter
+        # Set the default "formatter_class" to SortedHelpFormatter
+        if "formatter_class" not in kwargs:
+            kwargs["formatter_class"] = SortedHelpFormatter
         super().__init__(*args, **kwargs)
 
     if sys.version_info < (3, 13):
@@ -1715,6 +1723,13 @@ class FlexibleArgumentParser(ArgumentParser):
             self._action_groups.append(group)
             return group
 
+    def format_help(self) -> str:
+        # Add tip about JSON arguments to the epilog
+        epilog = self.epilog or ""
+        if not epilog.startswith(FlexibleArgumentParser._json_tip):
+            self.epilog = FlexibleArgumentParser._json_tip + epilog
+        return super().format_help()
+
     def parse_args(  # type: ignore[override]
         self,
         args: list[str] | None = None,