srcmaps are byte-denominated, slither assumes char-denomination

[bohendo]

This is the contract I'm investigating as a proof of concept:

contract Test {
  function one() external view returns(uint256) {
      return 1;
  }
  // ││ Unicode Comment ││
  function two() external view returns(uint256) {
      return 2;
  }
}

Notice that the four vertical lines of the unicode comment are ascii art box-drawing characters, each is 3 bytes long. This file is therefore 185 characters long and 193 bytes long. (difference of 8 = 4 * (3-1))

cat src/Test.sol | wc -c -m
    185     193

This python script:

from crytic_compile import CryticCompile

file = "src/Test.sol"
cc = CryticCompile(file);

for su in cc.compilation_units[file].source_units.items():
    print(su[1].srcmaps_runtime)

prints:

{'Test': ['0:192:0:-:0', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '123:67', '184:1', '123:67', '', '', '160:25:1', '', '', '148:2', '133:18', '123:67:0', '', '', '', '', '', '', '18', '79:1', '18:67', '']}

The first chunk from 0-192 shows that the srcmaps provided by the solc platform are byte-denominated.

Slither encode files as utf8, therefore offsets interpreted as char-denominated.

In particular, this misalignment causes slither-mutate to fail. For example, it will mutate the one function of Test.sol fine, but all mutations after the unicode comment will be off-by-8.

[bohendo]

This bug seems to be downstream from solidity#14733

[bohendo]

resolved by slither#2648