fix: inspect union arguments for annotations (#195)

NoInject[T] = None has the runtime typehint NoInject[T] | None,
instead of the expected NoInject[T | None].
NoInject[str] = 'blarb' works as expected

Resolves #192

injector/__init__.py

@@ -1190,6 +1190,19 @@ def _infer_injected_bindings(callable: Callable, only_explicit_bindings: bool) -
             # mypy complains about this construct:
             #     error: The type alias is invalid in runtime context
             # See: https://github.com/python/mypy/issues/5354
+            union_metadata = {
+                metadata
+                for member in new_members
+                for metadata in getattr(member, '__metadata__', tuple())
+                if _is_specialization(member, Annotated)
+            }
+            if (
+                only_explicit_bindings
+                and _inject_marker not in union_metadata
+                or _noinject_marker in union_metadata
+            ):
+                del bindings[k]
+            else:
                 bindings[k] = new_union  # type: ignore
 
     return bindings

injector_test.py

@@ -11,7 +11,7 @@
 """Functional tests for the "Injector" dependency injection framework."""
 
 from contextlib import contextmanager
-from typing import Any, NewType
+from typing import Any, NewType, Optional
 import abc
 import sys
 import threading
@@ -1481,3 +1481,16 @@ def test_get_bindings():
         pass
 
     assert get_bindings(function8) == {}
+
+    # Default arguments to NoInject annotations should behave the same as noninjectable decorator w.r.t 'None'
+    @inject
+    @noninjectable('b')
+    def function9(self, a: int, b: Optional[str] = None):
+        pass
+
+    @inject
+    def function10(self, a: int, b: NoInject[Optional[str]] = None):
+        # b:s type is Union[NoInject[Union[str, None]], None]
+        pass
+
+    assert get_bindings(function9) == {'a': int} == get_bindings(function10)