hdl: make Const(enum_value) work.

Fixes #1413.

Author: wanda-phi

amaranth/hdl/_ast.py

@@ -1580,6 +1580,10 @@ def cast(obj):
 
     def __init__(self, value, shape=None, *, src_loc_at=0):
         # We deliberately do not call Value.__init__ here.
+        if isinstance(value, Enum):
+            if shape is None:
+                shape = Shape.cast(type(value))
+            value = value.value
         value = int(operator.index(value))
         if shape is None:
             shape = Shape(bits_for(value), signed=value < 0)

tests/test_hdl_ast.py

@@ -502,6 +502,20 @@ def test_hash(self):
         with self.assertRaises(TypeError):
             hash(Const(0))
 
+    def test_enum(self):
+        e1 = Const(UnsignedEnum.FOO)
+        self.assertIsInstance(e1, Const)
+        self.assertEqual(e1.shape(), unsigned(2))
+        e2 = Const(SignedEnum.FOO)
+        self.assertIsInstance(e2, Const)
+        self.assertEqual(e2.shape(), signed(2))
+        e3 = Const(TypedEnum.FOO)
+        self.assertIsInstance(e3, Const)
+        self.assertEqual(e3.shape(), unsigned(2))
+        e4 = Const(UnsignedEnum.FOO, 4)
+        self.assertIsInstance(e4, Const)
+        self.assertEqual(e4.shape(), unsigned(4))
+
     def test_shape_castable(self):
         class MockConstValue(ValueCastable):
             def __init__(self, value):