Fix generic type import with module path (#2858)

Author: koxudaxi

src/datamodel_code_generator/__main__.py

@@ -689,9 +689,16 @@ def _serialize_callable(args: tuple[type, ...]) -> str:
 
 
 def _get_origin_name(origin: type) -> str:
-    """Get the name of a generic origin."""
+    """Get the fully qualified name of a generic origin.
+
+    For types from builtins, typing, or collections.abc, returns just the name.
+    For other types (custom generics), returns module.name format.
+    """
     name = getattr(origin, "__name__", None)
     if name:
+        module = getattr(origin, "__module__", "")
+        if module and module not in {"builtins", "typing", "collections.abc"}:
+            return f"{module}.{name}"
         return name
 
     # Fallback for origins without __name__ (rare edge case)

tests/data/python/input_model/pydantic_models.py

@@ -2,11 +2,22 @@
 
 from __future__ import annotations
 
+from collections import UserDict
 from collections.abc import Callable, Mapping, Sequence
-from typing import Any, FrozenSet, Optional, Set, Type, Union
+from typing import Any, FrozenSet, Generic, Optional, Set, Type, TypeVar, Union
 
 from pydantic import BaseModel
 
+# Custom generic type for testing generic type import
+TK = TypeVar("TK")
+TV = TypeVar("TV")
+
+
+class CustomGenericDict(UserDict[TK, TV], Generic[TK, TV]):
+    """Custom generic dict for testing generic type import."""
+
+    pass
+
 
 class User(BaseModel):
     """User model with basic fields."""
@@ -86,3 +97,11 @@ class ModelWithUnionCallable(BaseModel):
 
     union_callback: Union[Callable[[str], str], int]
     raw_callable: Callable  # Callable without type args
+
+
+class ModelWithCustomGeneric(BaseModel):
+    """Model with custom generic type that requires module import."""
+
+    model_config = {"arbitrary_types_allowed": True}
+    custom_dict: CustomGenericDict[str, int]
+    optional_custom_dict: CustomGenericDict[str, str] | None

tests/test_input_model.py

@@ -727,6 +727,20 @@ def test_input_model_union_callable(tmp_path: Path) -> None:
     )
 
 
+@SKIP_PYDANTIC_V1
+def test_input_model_custom_generic_type_import(tmp_path: Path) -> None:
+    """Test that custom generic types are properly imported with full module path."""
+    run_input_model_and_assert(
+        input_model="tests.data.python.input_model.pydantic_models:ModelWithCustomGeneric",
+        output_path=tmp_path / "output.py",
+        expected_output_contains=[
+            "from tests.data.python.input_model.pydantic_models import CustomGenericDict",
+            "CustomGenericDict[str, int]",
+            "CustomGenericDict[str, str] | None",
+        ],
+    )
+
+
 # ============================================================================
 # --input-model-ref-strategy tests
 # ============================================================================