Handle nested BaseSettings without nested delimiter

Fixes #36

src/settings_doc/main.py

@@ -5,6 +5,7 @@
 import re
 import shutil
 from enum import Enum, auto
+from inspect import isclass
 from os import listdir
 from pathlib import Path
 from typing import Final, Iterator
@@ -61,6 +62,18 @@ def _model_fields_recursive(
                 prefix + field_name + env_nested_delimiter,
                 env_nested_delimiter,
             )
+        elif isclass(model_field.annotation) and issubclass(model_field.annotation, BaseSettings):
+            # There are nested fields that do not require a delimiter to be joined. Generate variable names recursively.
+            submodel_prefix = model_field.annotation.model_config.get("env_prefix", "")
+
+            if not submodel_prefix:
+                submodel_prefix = prefix + field_name + "_"
+
+            yield from _model_fields_recursive(
+                model_field.annotation,
+                submodel_prefix,
+                model_field.annotation.model_config.get("env_nested_delimiter", None),
+            )
         else:
             yield prefix + field_name, model_field
 

tests/fixtures/valid_settings.py

@@ -2,6 +2,7 @@
 
 from pydantic import AliasChoices, AliasPath, BaseModel, Field
 from pydantic_settings import BaseSettings, SettingsConfigDict
+from typing_extensions import Annotated
 
 SETTINGS_ATTR = "logging_level"
 SETTINGS_MARKDOWN_FIRST_LINE = f"# `{SETTINGS_ATTR}`\n"
@@ -107,3 +108,42 @@ class EnvPrefixAndNestedDelimiterSettings(BaseSettings):
 
     direct: str
     sub_model: SubModel
+
+
+class SimpleSubModel(BaseModel):
+    leaf: str
+
+
+class SettingsSubModelWithSubModel(BaseSettings):
+    model_config = SettingsConfigDict(env_prefix="PREFIX_SUB_MODEL_", env_nested_delimiter="__")
+
+    nested: str
+    sub_model_2: SimpleSubModel
+
+
+class SettingsWithSettingsSubModel(BaseSettings):
+    """Expected environment variables.
+
+    - `PREFIX_DIRECT`
+    - `PREFIX_SUB_MODEL_NESTED`
+    - `PREFIX_SUB_MODEL_SUB_MODEL_2__LEAF`
+    """
+
+    model_config = SettingsConfigDict(env_prefix="PREFIX_")
+
+    direct: str
+    sub_model_1: Annotated[SettingsSubModelWithSubModel, Field(default_factory=SettingsSubModelWithSubModel)]
+
+
+class SettingsSubModel(BaseSettings):
+    model_config = SettingsConfigDict(env_prefix="")
+    leaf: str
+
+
+class SettingsWithSettingsSubModelNoPrefixOrDelimiter(BaseSettings):
+    """Expected environment variables.
+
+    - `EMPTY_LOGGING_LEVEL`
+    """
+
+    my_leaf: SettingsSubModel

tests/integration/generate/test_import_module_path.py

@@ -17,6 +17,10 @@
     MultipleSettings,
     PossibleValuesSettings,
     RequiredSettings,
+    SettingsSubModel,
+    SettingsSubModelWithSubModel,
+    SettingsWithSettingsSubModel,
+    SettingsWithSettingsSubModelNoPrefixOrDelimiter,
     ValidationAliasChoicesSettings,
     ValidationAliasPathSettings,
     ValidationAliasSettings,
@@ -50,6 +54,10 @@ class TestImportModulePath:
                     EnvPrefixSettings: None,
                     EnvNestedDelimiterSettings: None,
                     EnvPrefixAndNestedDelimiterSettings: None,
+                    SettingsSubModelWithSubModel: None,
+                    SettingsWithSettingsSubModel: None,
+                    SettingsSubModel: None,
+                    SettingsWithSettingsSubModelNoPrefixOrDelimiter: None,
                 },
                 id="for a module with multiple matching classes",
             ),
@@ -69,6 +77,10 @@ class TestImportModulePath:
                     EnvPrefixSettings: None,
                     EnvNestedDelimiterSettings: None,
                     EnvPrefixAndNestedDelimiterSettings: None,
+                    SettingsSubModelWithSubModel: None,
+                    SettingsWithSettingsSubModel: None,
+                    SettingsSubModel: None,
+                    SettingsWithSettingsSubModelNoPrefixOrDelimiter: None,
                 },
                 id="for multiple modules with multiple matching classes",
             ),

tests/unit/test_dotenv.py

@@ -16,6 +16,8 @@
     ExamplesSettings,
     FullSettings,
     PossibleValuesSettings,
+    SettingsWithSettingsSubModel,
+    SettingsWithSettingsSubModelNoPrefixOrDelimiter,
     ValidationAliasChoicesSettings,
     ValidationAliasPathSettings,
     ValidationAliasSettings,
@@ -138,6 +140,24 @@ def should_generate_env_prefix_and_nested_delimiter(runner: CliRunner, mocker: M
         assert "prefix_sub_model__nested=" in actual_string
         assert "prefix_sub_model__deep__leaf=" in actual_string
 
+    @staticmethod
+    def should_generate_settings_with_settings_sub_model(runner: CliRunner, mocker: MockerFixture):
+        actual_string = run_app_with_settings(mocker, runner, SettingsWithSettingsSubModel, fmt="dotenv")
+
+        assert "prefix_direct=" in actual_string
+        assert "prefix_sub_model_nested=" in actual_string
+        assert "prefix_sub_model_sub_model_2__leaf=" in actual_string
+
+    @staticmethod
+    def should_generate_settings_with_settings_sub_model_no_prefix_or_delimiter(
+        runner: CliRunner, mocker: MockerFixture
+    ):
+        actual_string = run_app_with_settings(
+            mocker, runner, SettingsWithSettingsSubModelNoPrefixOrDelimiter, fmt="dotenv"
+        )
+
+        assert "my_leaf_leaf=" in actual_string
+
 
 @pytest.mark.skipif(sys.version_info < (3, 11), reason="StrEnum is not available in Python 3.10 and below")
 class TestDotEnvFormatFromStrEnum:

tests/unit/test_markdown.py

@@ -20,6 +20,8 @@
     MultipleSettings,
     PossibleValuesSettings,
     RequiredSettings,
+    SettingsWithSettingsSubModel,
+    SettingsWithSettingsSubModelNoPrefixOrDelimiter,
     ValidationAliasChoicesSettings,
     ValidationAliasPathSettings,
     ValidationAliasSettings,
@@ -225,6 +227,22 @@ def should_generate_env_prefix_and_nested_delimiter(runner: CliRunner, mocker: M
         assert "`prefix_sub_model__nested`" in actual_string
         assert "`prefix_sub_model__deep__leaf`" in actual_string
 
+    @staticmethod
+    def should_generate_settings_with_settings_sub_model(runner: CliRunner, mocker: MockerFixture):
+        actual_string = run_app_with_settings(mocker, runner, SettingsWithSettingsSubModel)
+
+        assert "`prefix_direct`" in actual_string
+        assert "`prefix_sub_model_nested`" in actual_string
+        assert "`prefix_sub_model_sub_model_2__leaf`" in actual_string
+
+    @staticmethod
+    def should_generate_settings_with_settings_sub_model_no_prefix_or_delimiter(
+        runner: CliRunner, mocker: MockerFixture
+    ):
+        actual_string = run_app_with_settings(mocker, runner, SettingsWithSettingsSubModelNoPrefixOrDelimiter)
+
+        assert "`my_leaf_leaf`" in actual_string
+
 
 @pytest.mark.skipif(sys.version_info < (3, 11), reason="StrEnum is not available in Python 3.10 and below")
 class TestMarkdownFormatFromStrEnum: