codegen panic when converting literal bytes to decimal

[cyberthirst]

Version Information

• vyper Version (output of vyper --version): b635696

What's your issue about?

Per @trocher
when calling _literal_decimal(), the compiler will crash:

@_input_types(IntegerT, BoolT, BytesM_T, BytesT)
def to_decimal(expr, arg, out_typ):
    _check_bytes(expr, arg, out_typ, 32)

    if isinstance(expr, vy_ast.Constant):
        return _literal_decimal(expr, arg.typ, out_typ)
    ...

This happens as trying to construct a Decimal from a bytes is not supported:

val = decimal.Decimal(expr.value)  # should work for Int, Decimal

The following code lead the compiler to panic:

# pragma enable-decimals
@external
def foo():
    a: decimal = convert(b'\x01\x02', decimal)
    b: decimal = convert(x'0102', decimal)

[cyberthirst]

this issue should not be fixed before: #4608

this is because:

Similarly, in convert.py::_literal_decimal(), in case the out type is signed, the HexBytes value is not sign-extended, note that in the current state of the codebase, this is not reachable because of Codegen panic when Converting literal bytes to decimal:
if isinstance(expr, (vy_ast.Hex, vy_ast.Bytes)) and out_typ.is_signed:
val = _signextend(expr, val, arg_typ)