[WIP] Adds initial support for kspec coverage tool

[rajeevgopalakrishna]

This PR adds support for a new kspec coverage tool.

Usage: slither-kspec-coverage contract.sol kspec.md

The tool currently checks which functions in the specified contract.sol have corresponding Klab specifications in the provided kspec.md. It outputs a table illustrating which contract functions have kspec funcs, kspec reached funcs or not covered funcs.

kspec funcs indicates contract functions that have corresponding Klab specifications. kspec reached funcs indicates contract functions that do not have corresponding Klab specifications themselves but are called by functions that do have Klab specifications. not covered funcs highlights contract functions that do not have corresponding Klab specifications. The last two categories of functions need attention because they do not have Klab coverage.

For example: slither-kspec-coverage ./kspec_coverage/test/token/token.sol ./kspec_coverage/test/token/spec.md produces:

+-----------------+---------------------------+-----------------------+---------------------+
| Contract Name   | kspec funcs               | kspec reached funcs   | not covered funcs   |
+=================+===========================+=======================+=====================+
| Token (100.00%) | transfer(address,uint256) | add(uint256,uint256)  |                     |
|                 |                           | sub(uint256,uint256)  |                     |
+-----------------+---------------------------+-----------------------+---------------------+
1/3 (33.33%) functions are directly covered by a kspec
2/3 (66.67%) functions are reached by a kspec
0/3 (0.00%) functions are not reached by a kspec
There is a 0.00% standard deviation among percentage of functions covered per contract

[montyly]

I think it is probably worth to add tests with inherited contracts, I am not sure the coverage works as expected in these cases.

[montyly]

We should also add unit tests to ensure it works on all the verified Solidity contracts from https://github.com/runtimeverification/verified-smart-contracts

[Xenomega]

I would refactor this code, it's weak and too order dependent/specific. I can imagine it causing bugs. It was just kept this way because it worked without issue for the specific codebase it was designed for.

[rajeevgopalakrishna]

Refactor complete. Uses json_utils.

[montyly]

I am closing this in profit of #364