[Bug-Candidate]: Echidna fails to shrink call (revert) + vm.roll + vm.warp into only vm.roll + vm.warp

[aviggiano]

Describe the issue:

Description

In some scenarios, Echidna generates a failing sequence that contains a call, a block roll and a timestamp warp, where the call reverts, but where going forward in time is a pre-requisite for the sequence.

Ideally, the shrank sequence would ditch the call and only keep the roll and warp. In addition to keeping the sequences smaller, this makes it easier to convert the reproducer to Foundry, as we don't need to manually trim the reverting call function

Code example to reproduce the issue:

N/A (closed source)

Version:

Echidna 2.3.0

Relevant log output:

N/A

[aviggiano]

Same as crytic/medusa#752

[elopez]

We should have this in place already; one of the things shrinking does is convert reverted calls to NoCall while keeping the delays

echidna/lib/Echidna/Shrink.hs

Line 62 in 344bcfe

replaceByNoCall tx = tx { call = NoCall }

NoCall would show as *wait* on the traces.

For instance, this contract

contract C {
    uint256 c;

    constructor() { c = 0xffffffffffffffffffffffff; }

    function g() public {
       if (c == 0xffffffffffffffffffffffff) {
         c = block.timestamp;
       }
    }

   function h() public {
      revert();
   }

    function f() public {
      assert (c + 1000000 > block.timestamp);
      revert();
    }
}

shrinks to

(I suppose we could do one additional pass and coalesce the wait to the next call though)

Do you have an example where this doesn't occur?

Related: we have some WIP efforts to refactor the shrinking if you'd like to try them out: #1385

[aviggiano]

I forgot to mention, this is in optimization mode

I'll share a POC soon