Don't crash on a parameters declared to have type Optional[T]

We may change the behaviour of this in the future but I think it's
important to not crash now.

CHANGES

@@ -14,6 +14,8 @@ Technically backwards incompatible:
   Python 3-style annotations are used. See
   https://www.python.org/dev/peps/pep-0484/#forward-references for details.
 
+  Optional parameters are treated as compulsory for the purpose of injection.
+
 0.11.1
 ------
 

injector.py

@@ -24,7 +24,7 @@
 import warnings
 from abc import ABCMeta, abstractmethod
 from collections import namedtuple
-from typing import Any, Generic, get_type_hints, TypeVar
+from typing import Any, Generic, get_type_hints, TypeVar, Union
 
 
 try:
@@ -921,6 +921,14 @@ def _infer_injected_bindings(callable):
     bindings.pop(spec.varargs, None)
     bindings.pop(spec.varkw, None)
 
+    for k, v in list(bindings.items()):
+        if v is not Any and issubclass(v, Union):
+            # We don't treat Optional parameters in any special way at the moment
+            union_members = v.__union_params__
+            new_members = tuple(set(union_members) - {type(None)})
+            new_union = Union[new_members]
+            bindings[k] = new_union
+
     return bindings
 
 

injector_test_py3.py

@@ -244,3 +244,11 @@ def fun(a: Any) -> None:
     # it quickly gets helpful when the stack gets deeper.
     with pytest.raises(CallError):
         injector.call_with_injection(fun)
+
+
+def test_optionals_are_ignored_for_now():
+    @inject
+    def fun(s: str = None):
+        return s
+
+    assert Injector().call_with_injection(fun) == ''