Abort when auto-correct causes an infinite loop.

[dblock]

This avoids future situations such as the one described in #1484. At the very least when you run into an infinite loop RuboCop won't hang and tell you where the loop occurs so you can go correct it, exclude a cop or report it as a bug.

Also maybe we should call InfiniteCorrectionLoop something else, like LifetimeSentenceLoop ;)

[bbatsov]

You might add a few comments here and there, as casual readers might not realise what this code's for.

[jonas054]

👍 Nicely done! But keep the line length down.

[dblock]

This is good to merge. I've also added --max-auto-correct-count to avoid having a potential infinite loop when a Cop continues to flag a violation even after it has been auto-corrected. This will avoid all infinite loops after a certain (default 50) count, and I think it's a necessary evil.

Another change is to make CopStore return another CopStore so you can chain filtering out cops, and introduce test cops that are ignored at runtime so that we don't need to hack collections of cops used exclusively in tests.

[jonas054]

@dblock I mostly agree. The first commit is all good. We've seen this problem a number of times, so a solution is most welcome.

The problem solved by the second commit is more rare, I think, but I seem to recall that it has happened before that corrections just add more and more space, for example, without end. But I really wish we could find a solution where we don't add another command line option. It seems an excessive measure for a rare problem. If we base the max loop count on the initial number of correctable offenses, wouldn't it be possible to choose a number that will not need customization?

[dblock]

I am totally open for suggestions, but I don't think there's any way to derive a number of max loops. You're looking at a misbehaving cop that keeps making a correction, no in a loop, but in the "adding a space each time" way. My spec does just that, it changes a class name to something random, so it will loop forever. So what's the maximum number there?

We could just hard-code the number at something high, like 128, just cause it's a power of 2, that would be just fine. In the usual case you don't have this problem anyway, so this is just a precaution.

Let me know what you want to do to move this PR forward (including ripping that part out).

[dblock]

I removed the questionable part about the second commit, so this is now only detecting infinite loops where the cop autocorrects something and then comes back to the original source. I will PR that later separately and we can discuss it there.

[dblock]

🍏

[jonas054]

Is this change whitespace only now? Seems unnecessary then.

[jonas054]

@dblock Good idea! The changes look good to me, apart from some added spaces.

[bbatsov]

The readme changes seem totally unrelated to me.

[dblock]

Ok, cleaned this up, removed unrelated things (will make separate PRs), fixed the rest of the comments.