Add support for Pydantic models in stubgen

mypy/stubgen.py

@@ -491,6 +491,7 @@ def __init__(
         self.processing_enum = False
         self.processing_dataclass = False
         self.dataclass_field_specifier: tuple[str, ...] = ()
+        self.processing_pydantic_model = False
 
     @property
     def _current_class(self) -> ClassDef | None:
@@ -808,6 +809,14 @@ def visit_class_def(self, o: ClassDef) -> None:
         if self.analyzed and (spec := find_dataclass_transform_spec(o)):
             self.processing_dataclass = True
             self.dataclass_field_specifier = spec.field_specifiers
+        is_pydantic_model = False
+        for base_type_expr in o.base_type_exprs:
+            if isinstance(base_type_expr, (NameExpr, MemberExpr)) and self.get_fullname(
+                base_type_expr
+            ).endswith("BaseModel"):
+                is_pydantic_model = True
+                break
+        self.processing_pydantic_model = is_pydantic_model
         super().visit_class_def(o)
         self.dedent()
         self._vars.pop()
@@ -825,6 +834,7 @@ def visit_class_def(self, o: ClassDef) -> None:
         self.dataclass_field_specifier = ()
         self._class_stack.pop(-1)
         self.processing_enum = False
+        self.processing_pydantic_model = False
 
     def get_base_types(self, cdef: ClassDef) -> list[str]:
         """Get list of base classes for a class."""
@@ -1289,6 +1299,9 @@ def get_assign_initializer(self, rvalue: Expression) -> str:
             if not (isinstance(rvalue, TempNode) and rvalue.no_rhs):
                 return " = ..."
         # TODO: support other possible cases, where initializer is important
+        if self.processing_pydantic_model:
+            if not (isinstance(rvalue, TempNode) and rvalue.no_rhs):
+                return " = ..."
 
         # By default, no initializer is required:
         return ""

test-data/unit/stubgen.test

@@ -4718,3 +4718,121 @@ class DCMeta(type): ...
 
 class DC(metaclass=DCMeta):
     x: str
+
+[case testPydanticBaseModel]
+import pydantic
+
+class User(pydantic.BaseModel):
+    id: int
+    name: str
+    active: bool = True
+    optional_field: str | None = None
+[out]
+import pydantic
+
+class User(pydantic.BaseModel):
+    id: int
+    name: str
+    active: bool = ...
+    optional_field: str | None = ...
+
+[case testPydanticBaseModelWithAnnotationsOnly]
+import pydantic
+
+class ConfigSettings(pydantic.BaseModel):
+    # Fields without initialization
+    db_name: str
+    port: int
+    debug: bool
+[out]
+import pydantic
+
+class ConfigSettings(pydantic.BaseModel):
+    db_name: str
+    port: int
+    debug: bool
+
+[case testPydanticNestedBaseModel]
+from pydantic import BaseModel
+
+class Address(BaseModel):
+    street: str
+    city: str
+
+class User(BaseModel):
+    name: str
+    age: int
+    address: Address | None = None
+[out]
+from pydantic import BaseModel
+
+class Address(BaseModel):
+    street: str
+    city: str
+
+class User(BaseModel):
+    name: str
+    age: int
+    address: Address | None = ...
+
+[case testPydanticBaseModelComplex]
+from pydantic import BaseModel
+from typing import Dict, List, Optional, Union
+
+class Item(BaseModel):
+    name: str
+    description: Optional[str] = None
+    tags: List[str] = []
+    properties: Dict[str, Union[str, int, float, bool]] = {}
+[out]
+from pydantic import BaseModel
+
+class Item(BaseModel):
+    name: str
+    description: str | None = ...
+    tags: list[str] = ...
+    properties: dict[str, str | int | float | bool] = ...
+
+[case testPydanticBaseModelInheritance]
+from pydantic import BaseModel
+
+class BaseUser(BaseModel):
+    id: int
+    active: bool = True
+
+class User(BaseUser):
+    name: str
+    email: str
+[out]
+from pydantic import BaseModel
+
+class BaseUser(BaseModel):
+    id: int
+    active: bool = ...
+
+class User(BaseUser):
+    name: str
+    email: str
+
+[case testPydanticModelWithMethods]
+from pydantic import BaseModel
+
+class User(BaseModel):
+    id: int
+    name: str
+
+    def get_display_name(self) -> str:
+        return f"User {self.name}"
+
+    @property
+    def display_id(self) -> str:
+        return f"ID: {self.id}"
+[out]
+from pydantic import BaseModel
+
+class User(BaseModel):
+    id: int
+    name: str
+    def get_display_name(self) -> str: ...
+    @property
+    def display_id(self) -> str: ...