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lib.enum: check member value shapes before subclassing. NFCI

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This commit is a preparation for accepting const-castable expressions
as enum member values.

See #755.
This commit is contained in:
Catherine 2023-05-12 14:20:45 +00:00
parent 5f6b36e91f
commit bf8bbb0f63
2 changed files with 28 additions and 21 deletions
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38
amaranth/lib/enum.py
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@ -30,34 +30,42 @@ class EnumMeta(ShapeCastable, py_enum.EnumMeta):
return super().__prepare__(name, bases, **kwargs)
def __new__(metacls, name, bases, namespace, shape=None, **kwargs):
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
# the values of every member can be cast to the provided shape without truncation.
cls._amaranth_shape_ = shape = Shape.cast(shape)
for member in cls:
try:
member_shape = Const.cast(member.value).shape()
except TypeError as e:
raise TypeError("Value of enumeration member {!r} must be "
shape = Shape.cast(shape)
for member_name, member_value in namespace.items():
if py_enum._is_sunder(member_name) or py_enum._is_dunder(member_name):
continue
try:
member_shape = Const.cast(member_value).shape()
except TypeError as e:
if shape is not None:
raise TypeError("Value {!r} of enumeration member {!r} must be "
"a constant-castable expression"
.format(member)) from e
.format(member_value, member_name)) from e
else:
continue
if shape is not None:
if member_shape.signed and not shape.signed:
warnings.warn(
message="Value of enumeration member {!r} is signed, but the enumeration "
"shape is {!r}" # the repr will be `unsigned(X)`
.format(member, shape),
message="Value {!r} of enumeration member {!r} is signed, but "
"the enumeration shape is {!r}" # the repr will be `unsigned(X)`
.format(member_value, member_name, shape),
category=SyntaxWarning,
stacklevel=2)
elif (member_shape.width > shape.width or
member_shape.width == shape.width and
shape.signed and not member_shape.signed):
warnings.warn(
message="Value of enumeration member {!r} will be truncated to "
message="Value {!r} of enumeration member {!r} will be truncated to "
"the enumeration shape {!r}"
.format(member, shape),
.format(member_value, member_name, shape),
category=SyntaxWarning,
stacklevel=2)
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
# the values of every member can be cast to the provided shape without truncation.
cls._amaranth_shape_ = shape
else:
# Shape is not provided explicitly. Behave the same as a standard enumeration;
# the lack of `_amaranth_shape_` attribute is used to emit a warning when such