cli: Add lazy imports and fail-fast config validation (RFC #9853) (#19368)

Co-authored-by: hnyls2002 <lsyincs@gmail.com>

python/sglang/cli/main.py

@@ -1,7 +1,5 @@
 import argparse
 
-from sglang.cli.generate import generate
-from sglang.cli.serve import serve
 from sglang.cli.utils import get_git_commit_hash
 from sglang.version import __version__
 
@@ -17,19 +15,17 @@ def main():
     # complex sub commands
     subparsers = parser.add_subparsers(dest="subcommand", required=True)
 
-    serve_parser = subparsers.add_parser(
+    subparsers.add_parser(
         "serve",
         help="Launch the SGLang server.",
-        add_help=False,  # Defer help to the specific parser
+        add_help=False,
     )
-    serve_parser.set_defaults(func=serve)
 
-    generate_parser = subparsers.add_parser(
+    subparsers.add_parser(
         "generate",
         help="Run inference on a multimodal model.",
-        add_help=False,  # Defer help to the specific parser
+        add_help=False,
     )
-    generate_parser.set_defaults(func=generate)
 
     # simple commands
     version_parser = subparsers.add_parser(
@@ -39,4 +35,14 @@ def main():
     version_parser.set_defaults(func=version)
 
     args, extra_argv = parser.parse_known_args()
-    args.func(args, extra_argv)
+
+    if args.subcommand == "serve":
+        from sglang.cli.serve import serve
+
+        serve(args, extra_argv)
+    elif args.subcommand == "generate":
+        from sglang.cli.generate import generate
+
+        generate(args, extra_argv)
+    elif args.subcommand == "version":
+        version(args, extra_argv)

python/sglang/cli/serve.py

@@ -111,8 +111,6 @@ def serve(args, extra_argv):
             from sglang.launch_server import run_server
             from sglang.srt.server_args import prepare_server_args
 
-            # Add a dummy argument for the program name, expected by prepare_server_args
-            # as it typically processes sys.argv
             server_args = prepare_server_args(dispatch_argv)
 
             run_server(server_args)