hdl._ast: Make AST nodes immutable.

Fixes #1067.

amaranth/hdl/_ast.py

@@ -1462,26 +1462,38 @@ class Const(Value, metaclass=_ConstMeta):
 
     def __init__(self, value, shape=None, *, src_loc_at=0):
         # We deliberately do not call Value.__init__ here.
-        self.value = int(operator.index(value))
+        value = int(operator.index(value))
         if shape is None:
-            shape = Shape(bits_for(self.value), signed=self.value < 0)
+            shape = Shape(bits_for(value), signed=value < 0)
         elif isinstance(shape, int):
-            shape = Shape(shape, signed=self.value < 0)
+            shape = Shape(shape, signed=value < 0)
         else:
-            if isinstance(shape, range) and self.value == shape.stop:
+            if isinstance(shape, range) and value == shape.stop:
                 warnings.warn(
-                    message="Value {!r} equals the non-inclusive end of the constant "
-                            "shape {!r}; this is likely an off-by-one error"
-                            .format(self.value, shape),
+                    message=f"Value {value!r} equals the non-inclusive end of the constant "
+                            f"shape {shape!r}; this is likely an off-by-one error",
                     category=SyntaxWarning,
                     stacklevel=3)
             shape = Shape.cast(shape, src_loc_at=1 + src_loc_at)
-        self.width  = shape.width
-        self.signed = shape.signed
-        if self.signed and self.value >> (self.width - 1) & 1:
-            self.value |= -(1 << self.width)
+        self._width  = shape.width
+        self._signed = shape.signed
+        if shape.signed and value >> (shape.width - 1) & 1:
+            value |= -(1 << shape.width)
         else:
-            self.value &= (1 << self.width) - 1
+            value &= (1 << shape.width) - 1
+        self._value = value
+
+    @property
+    def value(self):
+        return self._value
+
+    @property
+    def width(self):
+        return self._width
+
+    @property
+    def signed(self):
+        return self._signed
 
     def shape(self):
         return Shape(self.width, self.signed)
@@ -1500,8 +1512,16 @@ C = Const  # shorthand
 class Operator(Value):
     def __init__(self, operator, operands, *, src_loc_at=0):
         super().__init__(src_loc_at=1 + src_loc_at)
-        self.operator = operator
-        self.operands = [Value.cast(op) for op in operands]
+        self._operator = operator
+        self._operands = tuple(Value.cast(op) for op in operands)
+
+    @property
+    def operator(self):
+        return self._operator
+
+    @property
+    def operands(self):
+        return self._operands
 
     def shape(self):
         def _bitwise_binary_shape(a_shape, b_shape):
@@ -1614,9 +1634,21 @@ class Slice(Value):
             raise IndexError(f"Slice start {start} must be less than slice stop {stop}")
 
         super().__init__(src_loc_at=src_loc_at)
-        self.value = value
-        self.start = int(operator.index(start))
-        self.stop  = int(operator.index(stop))
+        self._value = value
+        self._start = int(operator.index(start))
+        self._stop  = int(operator.index(stop))
+
+    @property
+    def value(self):
+        return self._value
+
+    @property
+    def start(self):
+        return self._start
+
+    @property
+    def stop(self):
+        return self._stop
 
     def shape(self):
         return Shape(self.stop - self.start)
@@ -1645,10 +1677,26 @@ class Part(Value):
             raise TypeError("Part offset must be unsigned")
 
         super().__init__(src_loc_at=src_loc_at)
-        self.value  = value
-        self.offset = offset
-        self.width  = width
-        self.stride = stride
+        self._value  = value
+        self._offset = offset
+        self._width  = width
+        self._stride = stride
+
+    @property
+    def value(self):
+        return self._value
+
+    @property
+    def offset(self):
+        return self._offset
+
+    @property
+    def width(self):
+        return self._width
+
+    @property
+    def stride(self):
+        return self._stride
 
     def shape(self):
         return Shape(self.width)
@@ -1691,7 +1739,7 @@ class Cat(Value):
     """
     def __init__(self, *args, src_loc_at=0):
         super().__init__(src_loc_at=src_loc_at)
-        self.parts = []
+        parts = []
         for index, arg in enumerate(flatten(args)):
             if isinstance(arg, Enum) and (not isinstance(type(arg), ShapeCastable) or
                                           not hasattr(arg, "_amaranth_shape_")):
@@ -1706,7 +1754,12 @@ class Cat(Value):
                               "context; specify the width explicitly using C({}, {})"
                               .format(index + 1, arg, arg, bits_for(arg)),
                               SyntaxWarning, stacklevel=2 + src_loc_at)
-            self.parts.append(Value.cast(arg))
+            parts.append(Value.cast(arg))
+        self._parts = tuple(parts)
+
+    @property
+    def parts(self):
+        return self._parts
 
     def shape(self):
         return Shape(sum(len(part) for part in self.parts))
@@ -1784,8 +1837,8 @@ class Signal(Value, DUID, metaclass=_SignalMeta):
             shape = unsigned(1)
         else:
             shape = Shape.cast(shape, src_loc_at=1 + src_loc_at)
-        self.width  = shape.width
-        self.signed = shape.signed
+        self._width  = shape.width
+        self._signed = shape.signed
 
         # TODO(amaranth-0.7): remove
         if reset is not None:
@@ -1831,8 +1884,8 @@ class Signal(Value, DUID, metaclass=_SignalMeta):
                             .format(orig_init, shape),
                     category=SyntaxWarning,
                     stacklevel=2)
-        self.init = init.value
-        self.reset_less = bool(reset_less)
+        self._init = init.value
+        self._reset_less = bool(reset_less)
 
         if isinstance(orig_shape, range) and orig_init is not None and orig_init not in orig_shape:
             if orig_init == orig_shape.stop:
@@ -1843,21 +1896,21 @@ class Signal(Value, DUID, metaclass=_SignalMeta):
                 raise SyntaxError(
                     f"Initial value {orig_init!r} is not within the signal shape {orig_shape!r}")
 
-        self.attrs = OrderedDict(() if attrs is None else attrs)
+        self._attrs = OrderedDict(() if attrs is None else attrs)
 
         if decoder is not None:
             # The value representation is specified explicitly. Since we do not expose `hdl._repr`,
             # this is the only way to add a custom filter to the signal right now. The setter sets
             # `self._value_repr` as well as the compatibility `self.decoder`.
-            self.decoder = decoder
+            pass
         else:
             # If it's an enum, expose it via `self.decoder` for compatibility, whether it's a Python
             # enum or an Amaranth enum. This also sets the value representation, even for custom
             # shape-castables that implement their own `_value_repr`.
             if isinstance(orig_shape, type) and issubclass(orig_shape, Enum):
-                self.decoder = orig_shape
+                decoder = orig_shape
             else:
-                self.decoder = None
+                decoder = None
             # The value representation is specified implicitly in the shape of the signal.
             if isinstance(orig_shape, ShapeCastable):
                 # A custom shape-castable always has a `_value_repr`, at least the default one.
@@ -1869,24 +1922,6 @@ class Signal(Value, DUID, metaclass=_SignalMeta):
                 # Any other case is formatted as a plain integer.
                 self._value_repr = (Repr(FormatInt(), self),)
 
-    @property
-    def reset(self):
-        warnings.warn("`Signal.reset` is deprecated, use `Signal.init` instead",
-                      DeprecationWarning, stacklevel=2)
-        return self.init
-
-    @reset.setter
-    def reset(self, value):
-        warnings.warn("`Signal.reset` is deprecated, use `Signal.init` instead",
-                      DeprecationWarning, stacklevel=2)
-        self.init = value
-
-    @property
-    def decoder(self):
-        return self._decoder
-
-    @decoder.setter
-    def decoder(self, decoder):
         # Compute the value representation that will be used by Amaranth.
         if decoder is None:
             self._value_repr = (Repr(FormatInt(), self),)
@@ -1903,6 +1938,37 @@ class Signal(Value, DUID, metaclass=_SignalMeta):
                     return str(value)
             self._decoder = enum_decoder
 
+    @property
+    def width(self):
+        return self._width
+
+    @property
+    def signed(self):
+        return self._signed
+
+    @property
+    def init(self):
+        return self._init
+
+    @property
+    def reset(self):
+        warnings.warn("`Signal.reset` is deprecated, use `Signal.init` instead",
+                      DeprecationWarning, stacklevel=2)
+        return self._init
+
+    @property
+    def reset_less(self):
+        return self._reset_less
+
+    @property
+    def attrs(self):
+        # Would ideally be frozendict...
+        return self._attrs
+
+    @property
+    def decoder(self):
+        return self._decoder
+
     @classmethod
     def like(cls, other, *, name=None, name_suffix=None, init=None, reset=None, src_loc_at=0, **kwargs):
         """Create Signal based on another.
@@ -1970,7 +2036,11 @@ class ClockSignal(Value):
             raise TypeError(f"Clock domain name must be a string, not {domain!r}")
         if domain == "comb":
             raise ValueError(f"Domain '{domain}' does not have a clock")
-        self.domain = domain
+        self._domain = domain
+
+    @property
+    def domain(self):
+        return self._domain
 
     def shape(self):
         return Shape(1)
@@ -2006,8 +2076,16 @@ class ResetSignal(Value):
             raise TypeError(f"Clock domain name must be a string, not {domain!r}")
         if domain == "comb":
             raise ValueError(f"Domain '{domain}' does not have a reset")
-        self.domain = domain
-        self.allow_reset_less = allow_reset_less
+        self._domain = domain
+        self._allow_reset_less = allow_reset_less
+
+    @property
+    def domain(self):
+        return self._domain
+
+    @property
+    def allow_reset_less(self):
+        return self._allow_reset_less
 
     def shape(self):
         return Shape(1)
@@ -2032,8 +2110,16 @@ class AnyValue(Value, DUID):
         super().__init__(src_loc_at=src_loc_at)
         self.kind  = self.Kind(kind)
         shape = Shape.cast(shape, src_loc_at=1 + src_loc_at)
-        self.width  = shape.width
-        self.signed = shape.signed
+        self._width  = shape.width
+        self._signed = shape.signed
+
+    @property
+    def width(self):
+        return self._width
+
+    @property
+    def signed(self):
+        return self._signed
 
     def shape(self):
         return Shape(self.width, self.signed)
@@ -2147,8 +2233,16 @@ class Array(MutableSequence):
 class ArrayProxy(Value):
     def __init__(self, elems, index, *, src_loc_at=0):
         super().__init__(src_loc_at=1 + src_loc_at)
-        self.elems = elems
-        self.index = Value.cast(index)
+        self._elems = elems
+        self._index = Value.cast(index)
+
+    @property
+    def elems(self):
+        return self._elems
+
+    @property
+    def index(self):
+        return self._index
 
     def __getattr__(self, attr):
         return ArrayProxy([getattr(elem, attr) for elem in self.elems], self.index)
@@ -2245,8 +2339,16 @@ class Statement:
 class Assign(Statement):
     def __init__(self, lhs, rhs, *, src_loc_at=0):
         super().__init__(src_loc_at=src_loc_at)
-        self.lhs = Value.cast(lhs)
-        self.rhs = Value.cast(rhs)
+        self._lhs = Value.cast(lhs)
+        self._rhs = Value.cast(rhs)
+
+    @property
+    def lhs(self):
+        return self._lhs
+
+    @property
+    def rhs(self):
+        return self._rhs
 
     def _lhs_signals(self):
         return self.lhs._lhs_signals()
@@ -2273,13 +2375,25 @@ class Property(Statement, MustUse):
 
     def __init__(self, kind, test, *, name=None, src_loc_at=0):
         super().__init__(src_loc_at=src_loc_at)
-        self.kind   = self.Kind(kind)
-        self.test   = Value.cast(test)
-        self.name   = name
+        self._kind   = self.Kind(kind)
+        self._test   = Value.cast(test)
+        self._name   = name
         if not isinstance(self.name, str) and self.name is not None:
             raise TypeError("Property name must be a string or None, not {!r}"
                             .format(self.name))
 
+    @property
+    def kind(self):
+        return self._kind
+
+    @property
+    def test(self):
+        return self._test
+
+    @property
+    def name(self):
+        return self._name
+
     def _lhs_signals(self):
         return set()
 
@@ -2322,8 +2436,8 @@ class Switch(Statement):
         # be automatically traced, so whatever constructs a Switch may optionally provide it.
         self.case_src_locs = {}
 
-        self.test  = Value.cast(test)
-        self.cases = OrderedDict()
+        self._test  = Value.cast(test)
+        self._cases = OrderedDict()
         for orig_keys, stmts in cases.items():
             # Map: None -> (); key -> (key,); (key...) -> (key...)
             keys = orig_keys
@@ -2354,10 +2468,18 @@ class Switch(Statement):
                 new_keys = (*new_keys, key)
             if not isinstance(stmts, Iterable):
                 stmts = [stmts]
-            self.cases[new_keys] = Statement.cast(stmts)
+            self._cases[new_keys] = Statement.cast(stmts)
             if orig_keys in case_src_locs:
                 self.case_src_locs[new_keys] = case_src_locs[orig_keys]
 
+    @property
+    def test(self):
+        return self._test
+
+    @property
+    def cases(self):
+        return self._cases
+
     def _lhs_signals(self):
         return union((s._lhs_signals() for s in self.cases.values()), start=SignalSet())
 

tests/test_hdl_ast.py

@@ -1237,10 +1237,6 @@ class SignalTestCase(FHDLTestCase):
         with self.assertWarnsRegex(DeprecationWarning,
                 r"^`Signal.reset` is deprecated, use `Signal.init` instead$"):
             self.assertEqual(s1.reset, 0b111)
-        with self.assertWarnsRegex(DeprecationWarning,
-                r"^`Signal.reset` is deprecated, use `Signal.init` instead$"):
-            s1.reset = 0b010
-        self.assertEqual(s1.init, 0b010)
         with self.assertWarnsRegex(DeprecationWarning,
                 r"^`reset=` is deprecated, use `init=` instead$"):
             s2 = Signal.like(s1, reset=3)

tests/test_hdl_rec.py

@@ -194,20 +194,6 @@ class RecordTestCase(FHDLTestCase):
         r4 = Record.like(r1, name_suffix="foo")
         self.assertEqual(r4.name, "r1foo")
 
-    def test_like_modifications(self):
-        r1 = Record([("a", 1), ("b", [("s", 1)])])
-        self.assertEqual(r1.a.name, "r1__a")
-        self.assertEqual(r1.b.name, "r1__b")
-        self.assertEqual(r1.b.s.name, "r1__b__s")
-        r1.a.init = 1
-        r1.b.s.init = 1
-        r2 = Record.like(r1)
-        self.assertEqual(r2.a.init, 1)
-        self.assertEqual(r2.b.s.init, 1)
-        self.assertEqual(r2.a.name, "r2__a")
-        self.assertEqual(r2.b.name, "r2__b")
-        self.assertEqual(r2.b.s.name, "r2__b__s")
-
     def test_slice_tuple(self):
         r1 = Record([("a", 1), ("b", 2), ("c", 3)])
         r2 = r1["a", "c"]