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lib.enum: accept any const-castable expression as member value.

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This behavior was introduced by amaranth-lang/rfcs#4. See #755.
This commit is contained in:
Catherine 2023-05-12 14:47:21 +00:00
parent bf8bbb0f63
commit 4398575322
4 changed files with 69 additions and 24 deletions
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26
amaranth/lib/enum.py
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@ -1,7 +1,7 @@
import enum as py_enum
import warnings
from ..hdl.ast import Shape, ShapeCastable, Const
from ..hdl.ast import Value, Shape, ShapeCastable, Const
__all__ = py_enum.__all__
@ -32,11 +32,18 @@ class EnumMeta(ShapeCastable, py_enum.EnumMeta):
def __new__(metacls, name, bases, namespace, shape=None, **kwargs):
if shape is not None:
shape = Shape.cast(shape)
# Prepare enumeration members for instantiation. This logic is unfortunately very
# convoluted because it supports two very different code paths that need to share
# the emitted warnings.
for member_name, member_value in namespace.items():
if py_enum._is_sunder(member_name) or py_enum._is_dunder(member_name):
continue
# If a shape is specified ("Amaranth mode" of amaranth.lib.enum.Enum), then every
# member value must be a constant-castable expression. Otherwise ("Python mode" of
# amaranth.lib.enum.Enum) any value goes, since all enumerations accepted by
# the built-in Enum class must be also accepted by amaranth.lib.enum.Enum.
try:
member_shape = Const.cast(member_value).shape()
member_const = Const.cast(member_value)
except TypeError as e:
if shape is not None:
raise TypeError("Value {!r} of enumeration member {!r} must be "
@ -44,7 +51,21 @@ class EnumMeta(ShapeCastable, py_enum.EnumMeta):
.format(member_value, member_name)) from e
else:
continue
if isinstance(member_value, Value):
# The member value is an Amaranth value that is also constant-castable.
# It cannot be used in an enumeration as-is (since it doesn't return a boolean
# from comparison operators, and this is required by py_enum).
# Replace the member value with the integer value of the constant, per RFC 4.
# Note that we do this even if no shape is provided (and this class is emulating
# a Python enumeration); this is OK because we only need to accept everything that
# the built-in class accepts to be a drop-in replacement, but the built-in class
# does not accept Amaranth values.
# We use dict.__setitem__ since namespace is a py_enum._EnumDict that overrides
# __setitem__ to check if the name has been already used.
dict.__setitem__(namespace, member_name, member_const.value)
# If a shape was specified, check whether the member value is compatible with it.
if shape is not None:
member_shape = member_const.shape()
if member_shape.signed and not shape.signed:
warnings.warn(
message="Value {!r} of enumeration member {!r} is signed, but "
@ -61,6 +82,7 @@ class EnumMeta(ShapeCastable, py_enum.EnumMeta):
.format(member_value, member_name, shape),
category=SyntaxWarning,
stacklevel=2)
# Actually instantiate the enumeration class.
cls = py_enum.EnumMeta.__new__(metacls, name, bases, namespace, **kwargs)
if shape is not None:
# Shape is provided explicitly. Set the `_amaranth_shape_` attribute, and check that