Unexpected exception in call trace generation of __default__ function

[Leminkay]

Boa commit: f58c33cde50f6deaaeefff1136b18f92ef747c6b

Example:

import boa

name = "__default__"

code = f"""
@external
@pure
def {name}() -> uint256:
    raise
"""

ct = boa.loads(code)

try:
    res = getattr(ct, name)()
    print(res)
except Exception as e:
    print(e)

Reverting in the __default__ function will raise an exception:

Traceback (most recent call last):
  File "/home/lemy/otitanoboa/titanoboa/test_except.py", line 15, in <module>
    res = getattr(ct, name)()
  File "/home/lemy/otitanoboa/titanoboa/boa/contracts/vyper/vyper_contract.py", line 1075, in __call__
    return self.contract.marshal_to_python(computation, typ)
  File "/home/lemy/otitanoboa/titanoboa/boa/contracts/vyper/vyper_contract.py", line 782, in marshal_to_python
    self.handle_error(computation)
  File "/home/lemy/otitanoboa/titanoboa/boa/contracts/base_evm_contract.py", line 51, in handle_error
    raise strip_internal_frames(b) from b
  File "/home/lemy/otitanoboa/titanoboa/test_except.py", line 15, in <module>
    res = getattr(ct, name)()
boa.contracts.base_evm_contract.BoaError: <exception str() failed>

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/lemy/otitanoboa/titanoboa/test_except.py", line 18, in <module>
    print(e)
  File "/home/lemy/otitanoboa/titanoboa/boa/contracts/base_evm_contract.py", line 132, in __str__
    call_tree = str(self.call_trace)
  File "/home/lemy/otitanoboa/titanoboa/boa/contracts/call_trace.py", line 97, in __str__
    text = f"{' ' * self.depth * 4}{self.text}"
  File "/home/lemy/otitanoboa/titanoboa/boa/contracts/call_trace.py", line 103, in text
    text = self.source.format(self.input_data, self.output, self.is_error)
  File "/home/lemy/otitanoboa/titanoboa/boa/contracts/call_trace.py", line 15, in format
    in_ = self._format_input(input_)
  File "/home/lemy/otitanoboa/titanoboa/boa/contracts/call_trace.py", line 25, in _format_input
    decoded = abi_decode(self.args_abi_type, input_)
  File "/usr/lib/python3.10/functools.py", line 981, in __get__
    val = self.func(instance)
  File "/home/lemy/otitanoboa/titanoboa/boa/contracts/vyper/vyper_contract.py", line 1135, in args_abi_type
    schema, fn_t = self._func_t_helper
  File "/usr/lib/python3.10/functools.py", line 981, in __get__
    val = self.func(instance)
  File "/home/lemy/otitanoboa/titanoboa/boa/contracts/vyper/vyper_contract.py", line 1123, in _func_t_helper
    method_id_int = int(self.method_id.hex(), 16)
ValueError: invalid literal for int() with base 16: ''

Meanwhile, using the non-default function will work as expected:

========================================================================
[E] [52] <unknown>.foo:5() <0x>
========================================================================

Revert(b'')

<<unknown> at 0x0880cf17Bd263d3d3a5c09D2D86cCecA3CcbD97c, compiled with vyper-0.4.0+e9db8d9>
 <compiler: user raise>

  function "foo", line 5:4 
       4 def foo() -> uint256:
  ---> 5     raise
  -----------^
       6

Provides an empty method_id for the default function and hence crashes.