Vyper: Output `methodIdentifiers` in vyper-serve

[yudetamago]

Hi, I'm one of the authors of Vyper plugin for Remix.
Remix requires method identifies(4 bytes function signatures) of contracts to resolve the called function and correctly parse tx input/output in remix console.

As for Solidity, it's included in the compiler output (https://solidity.readthedocs.io/en/v0.4.25/using-the-compiler.html#output-description) so I want to add it to Vyper compiler, too.

I did a PoC implementation in our fork repository like this.
https://github.com/LayerXcom/vyper/commit/8d48ebd54096d290109cb7e3964a73128130f80c

For now, I'm waiting #1089 to be merged because it's going to change the format of output.
After that, I'll refine that code and add tests and then create PR :)

[jacqueswww]

Cool, will look at adding it as part of the combined_json output.

[nrryuya]

@jacqueswww
Thanks! Then we wait it.

[jacqueswww]

@nrryuya @yudetamago I just pushed on #1089, give the branch a go ;) (this should merge today I reckon, just needs a final :+1: ). I will also add a commit for vyper-serve to use the new compile call.

[yudetamago]

@jacqueswww
Thanks for merging #1089!
Unfortunately, I found a mistake (which is due to my PoC, sorry).

Post

@public
@constant
def f(_n: uint256) -> uint256:
    return _n

to vyper-serve, then the following error has occurres.

Listening on http://localhost:8000
----------------------------------------
Exception happened during processing of request from ('127.0.0.1', 58639)
Traceback (most recent call last):
  File "/Users/yudetamago/.pyenv/versions/3.6.5/lib/python3.6/socketserver.py", line 639, in process_request_thread
    self.finish_request(request, client_address)
  File "/Users/yudetamago/.pyenv/versions/3.6.5/lib/python3.6/socketserver.py", line 361, in finish_request
    self.RequestHandlerClass(request, client_address, self)
  File "/Users/yudetamago/.pyenv/versions/3.6.5/lib/python3.6/socketserver.py", line 696, in __init__
    self.handle()
  File "/Users/yudetamago/.pyenv/versions/3.6.5/lib/python3.6/http/server.py", line 418, in handle
    self.handle_one_request()
  File "/Users/yudetamago/.pyenv/versions/3.6.5/lib/python3.6/http/server.py", line 406, in handle_one_request
    method()
  File "./bin/vyper-serve", line 64, in do_POST
    response, status_code = self._compile(data)
  File "./bin/vyper-serve", line 89, in _compile
    output_type='dict',
  File "/Users/yudetamago/dev/project/layerx/vyper/venv/lib/python3.6/site-packages/vyper-0.1.0b4-py3.6.egg/vyper/compiler.py", line 110, in compile_codes
    raise exc
  File "/Users/yudetamago/dev/project/layerx/vyper/venv/lib/python3.6/site-packages/vyper-0.1.0b4-py3.6.egg/vyper/compiler.py", line 105, in compile_codes
    out.setdefault(contract_name, {})[output_format] = output_formats_map[output_format](code)
  File "/Users/yudetamago/dev/project/layerx/vyper/venv/lib/python3.6/site-packages/vyper-0.1.0b4-py3.6.egg/vyper/compiler.py", line 92, in <lambda>
    'method_identifiers': lambda code: parser.mk_method_identifiers(code)
  File "/Users/yudetamago/dev/project/layerx/vyper/venv/lib/python3.6/site-packages/vyper-0.1.0b4-py3.6.egg/vyper/parser/parser.py", line 147, in mk_method_identifiers
    o.append(s.get_method_identifier(code, global_ctx._contracts, global_ctx._custom_units))
  File "/Users/yudetamago/dev/project/layerx/vyper/venv/lib/python3.6/site-packages/vyper-0.1.0b4-py3.6.egg/vyper/signatures/function_signature.py", line 178, in get_method_identifier
    sig = FunctionSignature.get_full_sig(self.name, self.args, sigs, custom_units)
  File "/Users/yudetamago/dev/project/layerx/vyper/venv/lib/python3.6/site-packages/vyper-0.1.0b4-py3.6.egg/vyper/signatures/function_signature.py", line 69, in get_full_sig
    return func_name + '(' + ','.join([get_type(arg) for arg in args]) + ')'
TypeError: sequence item 0: expected str instance, NoneType found
----------------------------------------

This comes from in this line.
https://github.com/ethereum/vyper/blob/921bb80cf59c9be0067ed20e1a7b6ad0b59598b3/vyper/signatures/function_signature.py#L178
get_full_sig requires the list of ast arg, but self.args (which is the list of VariableRecord) is passed.