Add strict_settings option, allow runtime fallbacks for custom settings (#1557)

Author: sobolevn

README.md

@@ -311,6 +311,53 @@ If you encounter this error in your own code, you can either cast the `Promise`
 
 If this is reported on Django code, please report an issue or open a pull request to fix the type hints.
 
+### How to use a custom library to handle Django settings?
+
+Using something like [`django-split-settings`](https://github.com/wemake-services/django-split-settings) or [`django-configurations`](https://github.com/jazzband/django-configurations) will make it hard for mypy to infer your settings.
+
+This might also be the case when using something like:
+
+```python
+try:
+    from .local_settings import *
+except Exception:
+    pass
+```
+
+So, mypy would not like this code:
+
+```python
+from django.conf import settings
+
+settings.CUSTOM_VALUE  # E: 'Settings' object has no attribute 'CUSTOM_SETTING'
+```
+
+To handle this corner case we have a special setting `strict_settings` (`True` by default),
+you can switch it to `False` to always return `Any` and not raise any errors if runtime settings module has the given value,
+for example `pyproject.toml`:
+
+```toml
+[tool.django-stubs]
+strict_settings = false
+```
+
+or `mypy.ini`:
+
+```ini
+[mypy.plugins.django-stubs]
+strict_settings = false
+```
+
+And then:
+
+```python
+# Works:
+reveal_type(settings.EXISTS_IN_RUNTIME)  # N: Any
+
+# Errors:
+reveal_type(settings.MISSING)  # E: 'Settings' object has no attribute 'MISSING'
+```
+
 ## Related projects
 
 - [`awesome-python-typing`](https://github.com/typeddjango/awesome-python-typing) - Awesome list of all typing-related things in Python.

mypy_django_plugin/config.py

@@ -14,21 +14,23 @@
 (config)
 ...
 [mypy.plugins.django-stubs]
-    django_settings_module: str (required)
+django_settings_module = str (required)
+strict_settings = bool (default: true)
 ...
 """
 TOML_USAGE = """
 (config)
 ...
 [tool.django-stubs]
 django_settings_module = str (required)
+strict_settings = bool (default: true)
 ...
 """
 INVALID_FILE = "mypy config file is not specified or found"
 COULD_NOT_LOAD_FILE = "could not load configuration file"
-MISSING_SECTION = "no section [{section}] found".format
+MISSING_SECTION = "no section [{section}] found"
 MISSING_DJANGO_SETTINGS = "missing required 'django_settings_module' config"
-INVALID_SETTING = "invalid {key!r}: the setting must be a boolean".format
+INVALID_BOOL_SETTING = "invalid {key!r}: the setting must be a boolean"
 
 
 def exit_with_error(msg: str, is_toml: bool = False) -> NoReturn:
@@ -48,8 +50,9 @@ def exit_with_error(msg: str, is_toml: bool = False) -> NoReturn:
 
 
 class DjangoPluginConfig:
-    __slots__ = ("django_settings_module",)
+    __slots__ = ("django_settings_module", "strict_settings")
     django_settings_module: str
+    strict_settings: bool
 
     def __init__(self, config_file: Optional[str]) -> None:
         if not config_file:
@@ -75,7 +78,7 @@ def parse_toml_file(self, filepath: Path) -> None:
         try:
             config: Dict[str, Any] = data["tool"]["django-stubs"]
         except KeyError:
-            toml_exit(MISSING_SECTION(section="tool.django-stubs"))
+            toml_exit(MISSING_SECTION.format(section="tool.django-stubs"))
 
         if "django_settings_module" not in config:
             toml_exit(MISSING_DJANGO_SETTINGS)
@@ -84,6 +87,10 @@ def parse_toml_file(self, filepath: Path) -> None:
         if not isinstance(self.django_settings_module, str):
             toml_exit("invalid 'django_settings_module': the setting must be a string")
 
+        self.strict_settings = config.get("strict_settings", True)
+        if not isinstance(self.strict_settings, bool):
+            toml_exit(INVALID_BOOL_SETTING.format(key="strict_settings"))
+
     def parse_ini_file(self, filepath: Path) -> None:
         parser = configparser.ConfigParser()
         try:
@@ -94,9 +101,14 @@ def parse_ini_file(self, filepath: Path) -> None:
 
         section = "mypy.plugins.django-stubs"
         if not parser.has_section(section):
-            exit_with_error(MISSING_SECTION(section=section))
+            exit_with_error(MISSING_SECTION.format(section=section))
 
         if not parser.has_option(section, "django_settings_module"):
             exit_with_error(MISSING_DJANGO_SETTINGS)
 
         self.django_settings_module = parser.get(section, "django_settings_module").strip("'\"")
+
+        try:
+            self.strict_settings = parser.getboolean(section, "strict_settings", fallback=True)
+        except ValueError:
+            exit_with_error(INVALID_BOOL_SETTING.format(key="strict_settings"))

mypy_django_plugin/lib/helpers.py

@@ -333,7 +333,7 @@ def resolve_string_attribute_value(attr_expr: Expression, django_context: "Djang
         member_name = attr_expr.name
         if isinstance(attr_expr.expr, NameExpr) and attr_expr.expr.fullname == "django.conf.settings":
             if hasattr(django_context.settings, member_name):
-                return getattr(django_context.settings, member_name)  # type: ignore
+                return getattr(django_context.settings, member_name)  # type: ignore[no-any-return]
     return None
 
 

mypy_django_plugin/main.py

@@ -274,7 +274,11 @@ def get_attribute_hook(self, fullname: str) -> Optional[Callable[[AttributeConte
 
         # Lookup of a settings variable
         if class_name == fullnames.DUMMY_SETTINGS_BASE_CLASS:
-            return partial(settings.get_type_of_settings_attribute, django_context=self.django_context)
+            return partial(
+                settings.get_type_of_settings_attribute,
+                django_context=self.django_context,
+                plugin_config=self.plugin_config,
+            )
 
         info = self._get_typeinfo_or_none(class_name)
 

mypy_django_plugin/transformers/settings.py

@@ -3,6 +3,7 @@
 from mypy.types import AnyType, Instance, TypeOfAny, TypeType
 from mypy.types import Type as MypyType
 
+from mypy_django_plugin.config import DjangoPluginConfig
 from mypy_django_plugin.django.context import DjangoContext
 from mypy_django_plugin.lib import helpers
 
@@ -19,7 +20,9 @@ def get_user_model_hook(ctx: FunctionContext, django_context: DjangoContext) ->
     return TypeType(Instance(model_info, []))
 
 
-def get_type_of_settings_attribute(ctx: AttributeContext, django_context: DjangoContext) -> MypyType:
+def get_type_of_settings_attribute(
+    ctx: AttributeContext, django_context: DjangoContext, plugin_config: DjangoPluginConfig
+) -> MypyType:
     if not isinstance(ctx.context, MemberExpr):
         return ctx.default_attr_type
 
@@ -42,5 +45,12 @@ def get_type_of_settings_attribute(ctx: AttributeContext, django_context: Django
                     return ctx.default_attr_type
                 return sym.type
 
+    # Now, we want to check if this setting really exist in runtime.
+    # If it does, we just return `Any`, not to raise any false-positives.
+    # But, we cannot reconstruct the exact runtime type.
+    # See https://github.com/typeddjango/django-stubs/pull/1163
+    if not plugin_config.strict_settings and hasattr(django_context.settings, setting_name):
+        return AnyType(TypeOfAny.implementation_artifact)
+
     ctx.api.fail(f"'Settings' object has no attribute {setting_name!r}", ctx.context)
     return ctx.default_attr_type

tests/test_error_handling.py

@@ -11,7 +11,8 @@
 (config)
 ...
 [mypy.plugins.django-stubs]
-    django_settings_module: str (required)
+django_settings_module = str (required)
+strict_settings = bool (default: true)
 ...
 (django-stubs) mypy: error: {}
 """
@@ -21,6 +22,7 @@
 ...
 [tool.django-stubs]
 django_settings_module = str (required)
+strict_settings = bool (default: true)
 ...
 (django-stubs) mypy: error: {}
 """
@@ -52,6 +54,11 @@ def write_to_file(file_contents: str, suffix: Optional[str] = None) -> Generator
             "missing required 'django_settings_module' config",
             id="no-settings-given",
         ),
+        pytest.param(
+            ["[mypy.plugins.django-stubs]", "django_settings_module = some.module", "strict_settings = bad"],
+            "invalid 'strict_settings': the setting must be a boolean",
+            id="missing-settings-module",
+        ),
     ],
 )
 def test_misconfiguration_handling(capsys: Any, config_file_contents: List[str], message_part: str) -> None:
@@ -113,6 +120,15 @@ def test_handles_filename(capsys: Any, filename: str) -> None:
             "could not load configuration file",
             id="invalid toml",
         ),
+        pytest.param(
+            """
+            [tool.django-stubs]
+            django_settings_module = "some.module"
+            strict_settings = "a"
+            """,
+            "invalid 'strict_settings': the setting must be a boolean",
+            id="invalid strict_settings type",
+        ),
     ],
 )
 def test_toml_misconfiguration_handling(capsys: Any, config_file_contents, message_part) -> None:
@@ -124,29 +140,37 @@ def test_toml_misconfiguration_handling(capsys: Any, config_file_contents, messa
     assert error_message == capsys.readouterr().err
 
 
-def test_correct_toml_configuration() -> None:
+@pytest.mark.parametrize("boolean_value", ["true", "false"])
+def test_correct_toml_configuration(boolean_value: str) -> None:
     config_file_contents = """
     [tool.django-stubs]
     some_other_setting = "setting"
     django_settings_module = "my.module"
-    """
+    strict_settings = {}
+    """.format(
+        boolean_value
+    )
 
     with write_to_file(config_file_contents, suffix=".toml") as filename:
         config = DjangoPluginConfig(filename)
 
     assert config.django_settings_module == "my.module"
+    assert config.strict_settings is (boolean_value == "true")
 
 
-def test_correct_configuration() -> None:
+@pytest.mark.parametrize("boolean_value", ["true", "True", "false", "False"])
+def test_correct_configuration(boolean_value) -> None:
     """Django settings module gets extracted given valid configuration."""
     config_file_contents = "\n".join(
         [
             "[mypy.plugins.django-stubs]",
-            "\tsome_other_setting = setting",
-            "\tdjango_settings_module = my.module",
+            "some_other_setting = setting",
+            "django_settings_module = my.module",
+            f"strict_settings = {boolean_value}",
         ]
-    ).expandtabs(4)
+    )
     with write_to_file(config_file_contents) as filename:
         config = DjangoPluginConfig(filename)
 
     assert config.django_settings_module == "my.module"
+    assert config.strict_settings is (boolean_value.lower() == "true")

tests/typecheck/test_settings.yml

@@ -58,3 +58,42 @@
       main:4: error: 'Settings' object has no attribute 'NON_EXISTANT_SETTING'
       main:5: error: 'Settings' object has no attribute 'NON_EXISTANT_SETTING'
       main:5: note: Revealed type is "Any"
+
+
+-   case: settings_loaded_from_runtime_magic
+    disable_cache: true
+    main: |
+        from django.conf import settings
+
+        # Global:
+        reveal_type(settings.SECRET_KEY)  # N: Revealed type is "builtins.str"
+
+        # Custom:
+        reveal_type(settings.A)  # N: Revealed type is "Any"
+        reveal_type(settings.B)  # E: 'Settings' object has no attribute 'B' # N: Revealed type is "Any"
+    custom_settings: |
+        # Some code that mypy cannot analyze, but values exist in runtime:
+        exec('A = 1')
+    mypy_config: |
+        [mypy.plugins.django-stubs]
+        django_settings_module = mysettings
+        strict_settings = false
+
+
+-   case: settings_loaded_from_runtime_magic_strict_default
+    disable_cache: true
+    main: |
+        from django.conf import settings
+
+        # Global:
+        reveal_type(settings.SECRET_KEY)  # N: Revealed type is "builtins.str"
+
+        # Custom:
+        reveal_type(settings.A)  # E: 'Settings' object has no attribute 'A' # N: Revealed type is "Any"
+        reveal_type(settings.B)  # E: 'Settings' object has no attribute 'B' # N: Revealed type is "Any"
+    custom_settings: |
+        # Some code that mypy cannot analyze, but values exist in runtime:
+        exec('A = 1')
+    mypy_config: |
+        [mypy.plugins.django-stubs]
+        django_settings_module = mysettings