feat: infer LLL IR function return values without metadata

[hedgar2017]

What ❔

Instead of querying special function metadata returned by vyper, I am trying to do it by analyzing the function LLL IR.

Such LLL IR must contain:

"var_list": [
    "return_buffer",
    "return_pc"
]

If this pattern is present, function has a single return value which is the return data offset.

Why ❔

The metadata seems to partly broken in vyper v0.4.0.

Fixes #119

Checklist

• PR title corresponds to the body of PR.
• Tests for the changes have been added / updated.
• Documentation comments have been added / updated.
• Code has been formatted via cargo fmt and checked with cargo clippy.

[codecov]

Codecov Report

Attention: Patch coverage is 28.20513% with 28 lines in your changes missing coverage. Please review.

Project coverage is 64.18%. Comparing base (6e59f49) to head (2f674f6).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...ect/contract/vyper/expression/instruction/label.rs	0.00%	19 Missing ⚠️
src/project/contract/vyper/function.rs	52.63%	9 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #120      +/-   ##
==========================================
- Coverage   64.79%   64.18%   -0.62%     
==========================================
  Files          56       54       -2     
  Lines        4420     4381      -39     
==========================================
- Hits         2864     2812      -52     
- Misses       1556     1569      +13     

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[charles-cooper]

might be related -- vyperlang/vyper#4312

[hedgar2017]

@charles-cooper yeah, that's indeed the cause.
But I've switched to checking for the var_list with return_buffer+return_pc, and it seems to be working like a charm!
Do you have any concerns about not using the metadata anymore?

[charles-cooper]

@charles-cooper yeah, that's indeed the cause. But I've switched to checking for the var_list with return_buffer+return_pc, and it seems to be working like a charm! Do you have any concerns about not using the metadata anymore?

It should be fine. The only issue is if you need other info from the metadata.