Handle balance overflow as evm exception

[cgewecke]

Revival of #676

Includes review fixes by @evertonfraga

Addresses #672.

Have made a minimal reproduction of #672 at cgewecke/checkpoint-repro. It runs two transactions vs. ganache-core:

• the first overflows an account balance and errors as expected with Value overflow
• the second fails with Cannot get state root with uncommitted checkpoints, indicating that the previous tx has left the vm in an unresolved state.

This happens because the balance overflow error is thrown directly from evm._executeCall and evm._executeCreate without being handled via the revert/commit steps in the method which calls them (evm.executeMessage)

PR

• returns Value overflow exceptions as part of the vm result (instead of throwing), similar to the way contract creation address collisions are handled
• makes Value overflow a VMError
• modifies the existing overflow test to inspect the result error and verify that the checkpoint count is 0 when runTx completes
• adds a balance overflow test for contract creation txs

NB: Looks like invalid precompiles also trigger an uncontrolled throw (here). Haven't addressed that but if this PR is the correct approach, perhaps that could be resolved here as well.

[evertonfraga]

Thanks! That's approved.

[cgewecke]

codecov is erroring on a negative diff change but I don't see one. Not sure what's happening there.

codecov/project — 90.98% (+-0.01%) compared to 7eb3217

[evertonfraga]

Codecov uses a quite confusing notation for coverage. There are two metrics:

The codecov/patch check refers only to the changes we made, and that's fully covered:

The codecov/project check compares to the parent commit, which is usually master, but in this case, your original commit.

I assume that was just a rounding error, the change looks 👌 and there are tests for it.

[holgerd77]

@evertonfraga if possible we should also add some pragmatic thresholds here for CodeCov (this was at least possible for Coveralls), so to allow for minor decreases (like 0.5% or so, eventually a bit less) together with some absolute threshold not be allowed to fall below. These little decreases occur all the time (e.g. on 1-2 liner PRs without tests, rewriting little things/splitting stuff up for clarity,...). This gets annoying without some basic flexibility.

[evertonfraga]

Yes! I have just described tweaking config in this issue: #723