lib.wiring: create flipped interface from flipped signature.

Fixes #914.

Co-authored-by: Nelson Gauthier <nelson.gauthier@gmail.com>

amaranth/lib/wiring.py

@@ -535,6 +535,9 @@ class FlippedSignature:
     def __setattr__(self, name, value):
         return setattr(self.__unflipped, name, value)
 
+    def create(self, *, path=()):
+        return flipped(self.__unflipped.create(path=path))
+
     def __repr__(self):
         return f"{self.__unflipped!r}.flip()"
 

tests/test_lib_wiring.py

@@ -584,6 +584,18 @@ class FlippedInterfaceTestCase(unittest.TestCase):
                 r"^flipped\(\) can only flip an interface object, not Signature\({}\)$"):
             flipped(Signature({}))
     
+    def test_create_subclass_flipped(self):
+        class CustomInterface(Interface):
+            def custom_method(self):
+                return 69
+        
+        class CustomSignature(Signature):
+            def create(self, *, path=()):
+                return CustomInterface(self, path=path)
+        
+        flipped_interface = CustomSignature({}).flip().create()
+        self.assertTrue(hasattr(flipped_interface, "custom_method"))
+
 
 class ConnectTestCase(unittest.TestCase):
     def test_arg_handles_and_signature_attr(self):