[Bugfix] Override dunder methods of placeholder modules (#11882)

Signed-off-by: DarkLight1337 <tlleungac@connect.ust.hk>

tests/test_utils.py

@@ -7,9 +7,9 @@ import pytest
 import torch
 from vllm_test_utils import monitor
 
-from vllm.utils import (FlexibleArgumentParser, StoreBoolean, deprecate_kwargs,
-                        get_open_port, memory_profiling, merge_async_iterators,
-                        supports_kw)
+from vllm.utils import (FlexibleArgumentParser, PlaceholderModule,
+                        StoreBoolean, deprecate_kwargs, get_open_port,
+                        memory_profiling, merge_async_iterators, supports_kw)
 
 from .utils import error_on_warning, fork_new_process_for_each_test
 
@@ -323,3 +323,44 @@ def test_memory_profiling():
     del weights
     lib.cudaFree(handle1)
     lib.cudaFree(handle2)
+
+
+def test_placeholder_module_error_handling():
+    placeholder = PlaceholderModule("placeholder_1234")
+
+    def build_ctx():
+        return pytest.raises(ModuleNotFoundError,
+                             match="No module named")
+
+    with build_ctx():
+        int(placeholder)
+
+    with build_ctx():
+        placeholder()
+
+    with build_ctx():
+        _ = placeholder.some_attr
+
+    with build_ctx():
+        # Test conflict with internal __name attribute
+        _ = placeholder.name
+
+    # OK to print the placeholder or use it in a f-string
+    _ = repr(placeholder)
+    _ = str(placeholder)
+
+    # No error yet; only error when it is used downstream
+    placeholder_attr = placeholder.placeholder_attr("attr")
+
+    with build_ctx():
+        int(placeholder_attr)
+
+    with build_ctx():
+        placeholder_attr()
+
+    with build_ctx():
+        _ = placeholder_attr.some_attr
+
+    with build_ctx():
+        # Test conflict with internal __module attribute
+        _ = placeholder_attr.module