tools: lint for dangling commas

[Trott]

Lint for dangling commas in the final lines of object/array declarations.

The no-dangling-comma-on-final-line instances (over 4000) in the code base vastly outnumber the dangling comma instances (less than 80, mostly in tests). So, for consistency, convert those ~80 instances to the dominant practice.

[Trott]

CI: https://ci.nodejs.org/job/node-test-pull-request/1553/

[Fishrock123]

Why?

It's actually potentially less churn into the future to enforce dangling commas in object literals since that means you never have to edit the previous land line.

[bnoordhuis]

I'm with Jeremiah. I like dangling commas, they keep diff noise down.

[Fishrock123]

Mind you since the no-comma style apparently that style has 4000 instances that probably isn't viable. I move we just don't do anything honestly.

[bnoordhuis]

Right, I'm not saying we update everything in one fell swoop. It would be nice if we could enforce it for new code, though.

[Trott]

@Fishrock123 @bnoordhuis I too am a fan of the dangling comma. I'm just a bigger fan of consistent coding conventions enforced by tooling. But yeah, you're not wrong, for sure.

[rvagg]

oo! let's go wholesale comma-first, that's one I can get behind and it defiantly reduces diff noise!