✨ Add None default value to fields in Optional[T] = Field() (#72)

bump_pydantic/codemods/add_default_none.py

@@ -56,7 +56,7 @@ def leave_ClassDef(self, original_node: cst.ClassDef, updated_node: cst.ClassDef
         self.inside_base_model = False
         return updated_node
 
-    def visit_AnnAssign(self, node: cst.AnnAssign) -> bool | None:
+    def visit_AnnAssign(self, node: cst.AnnAssign) -> None:
         if m.matches(
             node.annotation.annotation,
             m.Subscript(m.Name("Optional") | m.Attribute(m.Name("typing"), m.Name("Optional")))
@@ -75,11 +75,29 @@ def visit_AnnAssign(self, node: cst.AnnAssign) -> bool | None:
             | m.BinaryOperation(operator=m.BitOr(), right=m.Name("None")),
         ):
             self.should_add_none = True
-        return super().visit_AnnAssign(node)
+        return None
 
     def leave_AnnAssign(self, original_node: cst.AnnAssign, updated_node: cst.AnnAssign) -> cst.AnnAssign:
-        if self.inside_base_model and self.should_add_none and updated_node.value is None:
-            updated_node = updated_node.with_changes(value=cst.Name("None"))
+        if self.inside_base_model and self.should_add_none:
+            if updated_node.value is None:
+                updated_node = updated_node.with_changes(value=cst.Name("None"))
+            # TODO: Should accept `pydantic.Field` as well.
+            elif m.matches(updated_node.value, m.Call(func=m.Name("Field"))):
+                assert isinstance(updated_node.value, cst.Call)
+                if updated_node.value.args:
+                    arg = updated_node.value.args[0]
+                    if (arg.keyword is None or arg.keyword.value == "default") and m.matches(arg.value, m.Ellipsis()):
+                        updated_node = updated_node.with_changes(
+                            value=updated_node.value.with_changes(
+                                args=[arg.with_changes(value=cst.Name("None")), *updated_node.value.args[1:]]
+                            )
+                        )
+                # This is the case where `Field` is called without any arguments e.g. `Field()`.
+                else:
+                    updated_node = updated_node.with_changes(
+                        value=updated_node.value.with_changes(args=[cst.Arg(value=cst.Name("None"))])  # type: ignore
+                    )
+
         self.inside_an_assign = False
         self.should_add_none = False
         return updated_node

tests/integration/cases/__init__.py

@@ -4,8 +4,8 @@
 from .add_none import cases as add_none_cases
 from .base_settings import cases as base_settings_cases
 from .config_to_model import cases as config_to_model_cases
+from .field import cases as generic_model_cases
 from .folder_inside_folder import cases as folder_inside_folder_cases
-from .generic_model import cases as generic_model_cases
 from .is_base_model import cases as is_base_model_cases
 from .replace_validator import cases as replace_validator_cases
 from .root_model import cases as root_model_cases

tests/integration/cases/add_none.py

@@ -9,7 +9,7 @@
             content=[
                 "from typing import Any, Dict, Optional, Union",
                 "",
-                "from pydantic import BaseModel",
+                "from pydantic import BaseModel, Field",
                 "",
                 "",
                 "class A(BaseModel):",
@@ -18,14 +18,18 @@
                 "    c: Union[int, None]",
                 "    d: Any",
                 "    e: Dict[str, str]",
+                "    f: Optional[int] = Field(..., lt=10)",
+                "    g: Optional[int] = Field()",
+                "    h: Optional[int] = Field(...)",
+                "    i: Optional[int] = Field(default_factory=lambda: None)",
             ],
         ),
         expected=File(
             "add_none.py",
             content=[
                 "from typing import Any, Dict, Optional, Union",
                 "",
-                "from pydantic import BaseModel",
+                "from pydantic import BaseModel, Field",
                 "",
                 "",
                 "class A(BaseModel):",
@@ -34,6 +38,10 @@
                 "    c: Union[int, None] = None",
                 "    d: Any = None",
                 "    e: Dict[str, str]",
+                "    f: Optional[int] = Field(None, lt=10)",
+                "    g: Optional[int] = Field(None)",
+                "    h: Optional[int] = Field(None)",
+                "    i: Optional[int] = Field(default_factory=lambda: None)",
             ],
         ),
     )