Add .required() for configuration option

src/dependency_injector/providers.pxd

@@ -98,6 +98,7 @@ cdef class ConfigurationOption(Provider):
     cdef tuple __name
     cdef object __root_ref
     cdef dict __children
+    cdef bint __required
     cdef object __cache
 
 

src/dependency_injector/providers.pyi

@@ -146,6 +146,7 @@ class ConfigurationOption(Provider[Any]):
     def as_int(self) -> TypedConfigurationOption[int]: ...
     def as_float(self) -> TypedConfigurationOption[float]: ...
     def as_(self, callback: _Callable[..., T], *args: Injection, **kwargs: Injection) -> TypedConfigurationOption[T]: ...
+    def required(self) -> ConfigurationOption: ...
     def update(self, value: Any) -> None: ...
     def from_ini(self, filepath: Union[Path, str]) -> None: ...
     def from_yaml(self, filepath: Union[Path, str]) -> None: ...

src/dependency_injector/providers.pyx

@@ -1172,10 +1172,11 @@ cdef class ConfigurationOption(Provider):
 
     UNDEFINED = object()
 
-    def __init__(self, name, root):
+    def __init__(self, name, root, required=False):
         self.__name = name
         self.__root_ref = weakref.ref(root)
         self.__children = {}
+        self.__required = required
         self.__cache = self.UNDEFINED
         super().__init__()
 
@@ -1193,7 +1194,7 @@ cdef class ConfigurationOption(Provider):
         if copied_root is None:
             copied_root = deepcopy(root, memo)
 
-        copied = self.__class__(copied_name, copied_root)
+        copied = self.__class__(copied_name, copied_root, self.__required)
         copied.__children = deepcopy(self.__children, memo)
 
         return copied
@@ -1229,7 +1230,7 @@ cdef class ConfigurationOption(Provider):
             return self.__cache
 
         root = self.__root_ref()
-        value = root.get(self._get_self_name())
+        value = root.get(self._get_self_name(), self.__required)
         self.__cache = value
         return value
 
@@ -1258,6 +1259,9 @@ cdef class ConfigurationOption(Provider):
     def as_(self, callback, *args, **kwargs):
         return TypedConfigurationOption(callback, self, *args, **kwargs)
 
+    def required(self):
+        return self.__class__(self.__name, self.__root_ref(), required=True)
+
     def override(self, value):
         if isinstance(value, Provider):
             raise Error('Configuration option can only be overridden by a value')
@@ -1452,12 +1456,15 @@ cdef class Configuration(Object):
     def get_name(self):
         return self.__name
 
-    def get(self, selector):
+    def get(self, selector, required=False):
         """Return configuration option.
 
         :param selector: Selector string, e.g. "option1.option2"
         :type selector: str
 
+        :param required: Required flag, raise error if required option is missing
+        :type required: bool
+
         :return: Option value.
         :rtype: Any
         """
@@ -1472,7 +1479,7 @@ cdef class Configuration(Object):
             value = value.get(key, self.UNDEFINED)
 
             if value is self.UNDEFINED:
-                if self.__strict:
+                if self.__strict or required:
                     raise Error('Undefined configuration option "{0}.{1}"'.format(self.__name, selector))
                 return None
 

tests/typing/configuration.py

@@ -21,3 +21,7 @@ config3 = providers.Configuration()
 int3: providers.Callable[int] = config3.option.as_int()
 float3: providers.Callable[float] = config3.option.as_float()
 int3_custom: providers.Callable[int] = config3.option.as_(int)
+
+# Test 4: to check required() method
+config4 = providers.Configuration()
+option4: providers.ConfigurationOption = config4.option.required()

tests/unit/providers/test_configuration_py2_py3.py

@@ -97,6 +97,31 @@ class ConfigTests(unittest.TestCase):
 
         self.assertEqual(value, decimal.Decimal('123.123'))
 
+    def test_required(self):
+        provider = providers.Callable(
+            lambda value: value,
+            self.config.a.required(),
+        )
+        with self.assertRaisesRegex(errors.Error, 'Undefined configuration option "config.a"'):
+            provider()
+
+    def test_required_no_side_effect(self):
+        _ = providers.Callable(
+            lambda value: value,
+            self.config.a.required(),
+        )
+        self.assertIsNone(self.config.a())
+
+    def test_required_as_(self):
+        provider = providers.List(
+            self.config.int_test.required().as_int(),
+            self.config.float_test.required().as_float(),
+            self.config._as_test.required().as_(decimal.Decimal),
+        )
+        self.config.from_dict({'int_test': '1', 'float_test': '2.0', '_as_test': '3.0'})
+
+        self.assertEqual(provider(), [1, 2.0, decimal.Decimal('3.0')])
+
     def test_providers_value_override(self):
         a = self.config.a
         ab = self.config.a.b