Add --model-config-parser registry for pluggable config formats (#25050)

Signed-off-by: Xingyu Liu <charlotteliu12x@gmail.com>

test/registered/unit/configs/test_model_config_parser_registry.py

@@ -0,0 +1,62 @@
+"""Unit tests for srt/configs/model_config_parser_registry.py"""
+
+import unittest
+
+from transformers import PretrainedConfig
+
+from sglang.srt.configs.model_config_parser_registry import (
+    _MODEL_CONFIG_PARSER_REGISTRY,
+    ModelConfigParserBase,
+    get_model_config_parser,
+    register_model_config_parser,
+)
+from sglang.test.ci.ci_register import register_cpu_ci
+from sglang.test.test_utils import CustomTestCase
+
+register_cpu_ci(est_time=1, suite="stage-a-test-cpu")
+
+
+class _FakeParser(ModelConfigParserBase):
+    def parse(self, model, trust_remote_code, revision=None, **kwargs):
+        return PretrainedConfig()
+
+
+class _AnotherFakeParser(ModelConfigParserBase):
+    def parse(self, model, trust_remote_code, revision=None, **kwargs):
+        return PretrainedConfig()
+
+
+class TestModelConfigParserRegistry(CustomTestCase):
+    def setUp(self):
+        self._saved_registry = dict(_MODEL_CONFIG_PARSER_REGISTRY)
+        _MODEL_CONFIG_PARSER_REGISTRY.clear()
+
+    def tearDown(self):
+        _MODEL_CONFIG_PARSER_REGISTRY.clear()
+        _MODEL_CONFIG_PARSER_REGISTRY.update(self._saved_registry)
+
+    def test_register_then_get_roundtrip(self):
+        register_model_config_parser("fake")(_FakeParser)
+        self.assertIsInstance(get_model_config_parser("fake"), _FakeParser)
+
+    def test_register_rejects_non_subclass(self):
+        class NotAParser:
+            pass
+
+        with self.assertRaises(ValueError) as ctx:
+            register_model_config_parser("bad")(NotAParser)
+        self.assertIn("ModelConfigParserBase", str(ctx.exception))
+
+    def test_unknown_name_raises_with_registered_list(self):
+        register_model_config_parser("fake")(_FakeParser)
+        register_model_config_parser("another")(_AnotherFakeParser)
+        with self.assertRaises(ValueError) as ctx:
+            get_model_config_parser("does-not-exist")
+        msg = str(ctx.exception)
+        self.assertIn("does-not-exist", msg)
+        self.assertIn("another", msg)
+        self.assertIn("fake", msg)
+
+
+if __name__ == "__main__":
+    unittest.main()