hdl.ast: do not cast comparand to shape in Shape.__eq__.

This doesn't match how other Python comparison operators work.
E.g. `1 == int("1")` but `1 != "1"`.

amaranth/hdl/ast.py

@@ -133,13 +133,8 @@ class Shape:
             return "unsigned({})".format(self.width)
 
     def __eq__(self, other):
-        if not isinstance(other, Shape):
-            try:
-                other = self.__class__.cast(other)
-            except TypeError as e:
-                raise TypeError("Shapes may be compared with shape-castable objects, not {!r}"
-                                .format(other)) from e
-        return self.width == other.width and self.signed == other.signed
+        return (isinstance(other, Shape) and
+                self.width == other.width and self.signed == other.signed)
 
 
 def unsigned(width):

amaranth/lib/data.py

@@ -38,7 +38,8 @@ class Field:
 
     def __eq__(self, other):
         return (isinstance(other, Field) and
-                self._shape == other.shape and self._offset == other.offset)
+                Shape.cast(self._shape) == Shape.cast(other.shape) and
+                self._offset == other.offset)
 
     def __repr__(self):
         return f"Field({self._shape!r}, {self._offset})"

tests/test_hdl_ast.py

@@ -47,15 +47,8 @@ class ShapeTestCase(FHDLTestCase):
                 r"^Width must be a non-negative integer, not -1$"):
             Shape(-1)
 
-    def test_compare_wrong(self):
-        with self.assertRaisesRegex(TypeError,
-                r"^Shapes may be compared with shape-castable objects, not 'hi'$"):
-            Shape(1, True) == 'hi'
-
-    def test_compare_tuple_wrong(self):
-        with self.assertRaisesRegex(TypeError,
-                r"^Shapes may be compared with shape-castable objects, not \(2, 3\)$"):
-            Shape(1, True) == (2, 3)
+    def test_compare_non_shape(self):
+        self.assertNotEqual(Shape(1, True), "hi")
 
     def test_repr(self):
         self.assertEqual(repr(Shape()), "unsigned(1)")

tests/test_lib_data.py

@@ -534,7 +534,7 @@ class StructTestCase(FHDLTestCase):
 
         v = S()
         self.assertEqual(Layout.of(v), S)
-        self.assertEqual(Value.cast(v).shape(), S)
+        self.assertEqual(Value.cast(v).shape(), Shape.cast(S))
         self.assertEqual(Value.cast(v).name, "v")
         self.assertRepr(v.a, "(slice (sig v) 0:1)")
         self.assertRepr(v.b, "(s (slice (sig v) 1:4))")
@@ -550,7 +550,7 @@ class StructTestCase(FHDLTestCase):
             a: unsigned(1)
             b: R
 
-        self.assertEqual(S, unsigned(9))
+        self.assertEqual(Shape.cast(S), unsigned(9))
 
         v = S()
         self.assertIs(Layout.of(v), S)
@@ -654,7 +654,7 @@ class UnionTestCase(FHDLTestCase):
 
         v = U()
         self.assertEqual(Layout.of(v), U)
-        self.assertEqual(Value.cast(v).shape(), U)
+        self.assertEqual(Value.cast(v).shape(), Shape.cast(U))
         self.assertRepr(v.a, "(slice (sig v) 0:1)")
         self.assertRepr(v.b, "(s (slice (sig v) 0:3))")
 
@@ -803,7 +803,7 @@ class RFCExamplesTestCase(TestCase):
             kind: Kind
             value: Value
 
-        self.assertEqual(SomeVariant, unsigned(3))
+        self.assertEqual(Shape.cast(SomeVariant), unsigned(3))
 
         view3 = SomeVariant()
         self.assertIsInstance(Value.cast(view3), Signal)