Fail build on unsupported rules

[cowwoc]

When building using grunt-jscs I get Warning: Unsupported rules: requireSpaceBeforeKeywords Use --force to continue.

Upgrading to a newer version of grunt-jscs fixes the problem but the underlying issue should get fixed. That is: don't silently skip jscs on an unknown rule, break the build instead so developers will notice the problem.

[gustavohenke]

That's an intended change. See this commit for reference.

[gustavohenke]

Any further questions, please ask!

[cowwoc]

@gustavohenke I understand that according to jscs-dev/node-jscs#334 this feature is meant to address forward-compatibility, but I (unless I misunderstood what is going on) I don't think it works as intended.

1. I agree that it's okay to ignore unsupported/unknown flags for forward compatibility.
2. The part I disagree with is that jscs should totally abort on unknown flags. Instead, I expect it to warn about the unknown flags, and run without them.

Did I misunderstand what is going on? Is JSCS still running (without the unknown flag) when this warning is issued?