[Doc] Add engine args back in to the docs (#20674)

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

docs/mkdocs/hooks/generate_argparse.py

@@ -0,0 +1,105 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+import logging
+import sys
+from argparse import SUPPRESS, HelpFormatter
+from pathlib import Path
+from typing import Literal
+from unittest.mock import MagicMock, patch
+
+ROOT_DIR = Path(__file__).parent.parent.parent.parent
+ARGPARSE_DOC_DIR = ROOT_DIR / "docs/argparse"
+
+sys.path.insert(0, str(ROOT_DIR))
+sys.modules["aiohttp"] = MagicMock()
+sys.modules["blake3"] = MagicMock()
+sys.modules["vllm._C"] = MagicMock()
+
+from vllm.engine.arg_utils import AsyncEngineArgs, EngineArgs  # noqa: E402
+from vllm.utils import FlexibleArgumentParser  # noqa: E402
+
+logger = logging.getLogger("mkdocs")
+
+
+class MarkdownFormatter(HelpFormatter):
+    """Custom formatter that generates markdown for argument groups."""
+
+    def __init__(self, prog):
+        super().__init__(prog,
+                         max_help_position=float('inf'),
+                         width=float('inf'))
+        self._markdown_output = []
+
+    def start_section(self, heading):
+        if heading not in {"positional arguments", "options"}:
+            self._markdown_output.append(f"\n### {heading}\n\n")
+
+    def end_section(self):
+        pass
+
+    def add_text(self, text):
+        if text:
+            self._markdown_output.append(f"{text.strip()}\n\n")
+
+    def add_usage(self, usage, actions, groups, prefix=None):
+        pass
+
+    def add_arguments(self, actions):
+        for action in actions:
+
+            option_strings = f'`{"`, `".join(action.option_strings)}`'
+            self._markdown_output.append(f"#### {option_strings}\n\n")
+
+            if choices := action.choices:
+                choices = f'`{"`, `".join(str(c) for c in choices)}`'
+                self._markdown_output.append(
+                    f"Possible choices: {choices}\n\n")
+
+            self._markdown_output.append(f"{action.help}\n\n")
+
+            if (default := action.default) != SUPPRESS:
+                self._markdown_output.append(f"Default: `{default}`\n\n")
+
+    def format_help(self):
+        """Return the formatted help as markdown."""
+        return "".join(self._markdown_output)
+
+
+def create_parser(cls, **kwargs) -> FlexibleArgumentParser:
+    """Create a parser for the given class with markdown formatting.
+    
+    Args:
+        cls: The class to create a parser for
+        **kwargs: Additional keyword arguments to pass to `cls.add_cli_args`.
+
+    Returns:
+        FlexibleArgumentParser: A parser with markdown formatting for the class.
+    """
+    parser = FlexibleArgumentParser()
+    parser.formatter_class = MarkdownFormatter
+    with patch("vllm.config.DeviceConfig.__post_init__"):
+        return cls.add_cli_args(parser, **kwargs)
+
+
+def on_startup(command: Literal["build", "gh-deploy", "serve"], dirty: bool):
+    logger.info("Generating argparse documentation")
+    logger.debug("Root directory: %s", ROOT_DIR.resolve())
+    logger.debug("Output directory: %s", ARGPARSE_DOC_DIR.resolve())
+
+    # Create the ARGPARSE_DOC_DIR if it doesn't exist
+    if not ARGPARSE_DOC_DIR.exists():
+        ARGPARSE_DOC_DIR.mkdir(parents=True)
+
+    # Create parsers to document
+    parsers = {
+        "engine_args": create_parser(EngineArgs),
+        "async_engine_args": create_parser(AsyncEngineArgs,
+                                           async_args_only=True),
+    }
+
+    # Generate documentation for each parser
+    for stem, parser in parsers.items():
+        doc_path = ARGPARSE_DOC_DIR / f"{stem}.md"
+        with open(doc_path, "w") as f:
+            f.write(parser.format_help())
+        logger.info("Argparse generated: %s", doc_path.relative_to(ROOT_DIR))