Add explicit error message when specifying default_return_value on void function call

[benber86]

What I did

When specifying the default_return_value on a call to a void external function, the compiler currently only returns the following error message AttributeError: 'NoneType' object has no attribute 'compare_type'.
I added a more explicit exception so that the error can be caught and addressed more easily.

How I did it

I added a check for a return type when default_return_value is set. If there's no return type, an ArgumentException is raised.

How to verify it

Compiling this contract:

interface FooBar:
    def foo(): payable

@external
def bar():
    FooBar(empty(address)).foo(default_return_value=True)

will now generate the following error:

vyper.exceptions.ArgumentException: default_return_value specified but foo is void
  contract "dist/simple.vy:6", function "bar", line 6:52 
       5 def bar():
  ---> 6     FooBar(empty(address)).foo(default_return_value=True)
  -----------------------------------------------------------^
       7

Commit message

Exception when setting default_return_value on void function call

Description for the changelog

Add explicit error message when specifying default_return_value on void function call

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[charles-cooper]

is there any case where require_return= should not be set to true?

[benber86]

is there any case where require_return= should not be set to true?

Not for the default_return_value kwarg specifically. Would you prefer something like if kwarg.arg == "default_return_value" over having a flag for it?

[codecov-commenter]

Codecov Report

Merging #3121 (c575665) into master (6020b8b) will decrease coverage by 0.27%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master    #3121      +/-   ##
==========================================
- Coverage   88.49%   88.21%   -0.28%     
==========================================
  Files          95       95              
  Lines       10758    10762       +4     
  Branches     2554     2267     -287     
==========================================
- Hits         9520     9494      -26     
- Misses        796      829      +33     
+ Partials      442      439       -3     

Impacted Files	Coverage Δ
vyper/semantics/types/function.py	86.51% <0.00%> (-0.66%)	⬇️
vyper/codegen/arithmetic.py	79.48% <0.00%> (-5.13%)	⬇️
vyper/semantics/types/value/numeric.py	80.45% <0.00%> (-4.60%)	⬇️
vyper/builtin_functions/functions.py	89.23% <0.00%> (-1.31%)	⬇️
vyper/compiler/output.py	89.06% <0.00%> (+0.05%)	⬆️
vyper/cli/vyper_json.py	79.09% <0.00%> (+0.07%)	⬆️

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