Determine RootModel complexity from root type

pydantic_settings/sources.py

@@ -35,7 +35,7 @@
 
 import typing_extensions
 from dotenv import dotenv_values
-from pydantic import AliasChoices, AliasPath, BaseModel, Json
+from pydantic import AliasChoices, AliasPath, BaseModel, Json, RootModel
 from pydantic._internal._repr import Representation
 from pydantic._internal._typing_extra import WithArgsTypes, origin_is_union, typing_base
 from pydantic._internal._utils import deep_update, is_model_class, lenient_issubclass
@@ -1904,6 +1904,16 @@ def read_env_file(
 
 
 def _annotation_is_complex(annotation: type[Any] | None, metadata: list[Any]) -> bool:
+    # If the model is a root model, the root annotation should be used to
+    # evaluate the complexity.
+    if isinstance(annotation, type) and issubclass(annotation, RootModel):
+        # In some rare cases (see test_root_model_as_field),
+        # the root attribute is not available. For these cases, python 3.8 and 3.9
+        # return 'RootModelRootType'.
+        root_annotation = annotation.__annotations__.get('root', None)
+        if root_annotation is not None and root_annotation != 'RootModelRootType':
+            annotation = root_annotation
+
     if any(isinstance(md, Json) for md in metadata):  # type: ignore[misc]
         return False
     # Check if annotation is of the form Annotated[type, metadata].

tests/test_settings.py

@@ -2,6 +2,7 @@
 import dataclasses
 import json
 import os
+import pathlib
 import re
 import sys
 import typing
@@ -2185,6 +2186,43 @@ class Settings(BaseSettings):
     assert s.model_dump() == {'z': [{'x': 1, 'y': {'foo': 1}}, {'x': 2, 'y': {'foo': 2}}]}
 
 
+def test_str_based_root_model(env):
+    """Testing to pass string directly to root model."""
+
+    class Foo(RootModel[str]):
+        root: str
+
+    class Settings(BaseSettings):
+        foo: Foo
+        plain: str
+
+    TEST_STR = 'hello world'
+    env.set('foo', TEST_STR)
+    env.set('plain', TEST_STR)
+    s = Settings()
+    assert s.model_dump() == {'foo': TEST_STR, 'plain': TEST_STR}
+
+
+def test_path_based_root_model(env):
+    """Testing to pass path directly to root model."""
+
+    class Foo(RootModel[pathlib.PurePosixPath]):
+        root: pathlib.PurePosixPath
+
+    class Settings(BaseSettings):
+        foo: Foo
+        plain: pathlib.PurePosixPath
+
+    TEST_PATH: str = '/hello/world'
+    env.set('foo', TEST_PATH)
+    env.set('plain', TEST_PATH)
+    s = Settings()
+    assert s.model_dump() == {
+        'foo': pathlib.PurePosixPath(TEST_PATH),
+        'plain': pathlib.PurePosixPath(TEST_PATH),
+    }
+
+
 def test_optional_field_from_env(env):
     class Settings(BaseSettings):
         x: Optional[str] = None