Style/TrailingCommaInArguments false positive with interpretation of multi-lined arguments?

[brandonweiss]

If I set this configuration:

Style/TrailingCommaInArguments:
  Enabled: true,
  EnforcedStyleForMultiline: consistent_comma

Then it enforces this code should have a comma like this:

EmailWorker.perform_async({
  subject: "hey there",
  email: "foo@bar.com"
},)

This doesn't seem right to me? It's a nuanced difference, but I don't consider this multi-lined arguments—the argument actually starts on the same line as the parentheses. The argument itself is multi-lined for readability, but the arguments aren't multi-lined. This is what I think multi-lined arguments look like:

EmailWorker.perform_async(
  "foo",
  "bar,
)

Or in the context of a hash:

EmailWorker.perform_async(
  {
    subject: "hey there",
    email: "foo@bar.com"
  },
)

Thoughts?

[jonas054]

I agree. The purpose of the trailing comma cops is to make it possible to enforce a style that minimizes the diff when another element is added at the end. And the comma in your example is useless for that purpose.

In this code from lib/rubocop/cop/mixin/trailing_comma.rb, we see that the intentions are correct, but the implementation is wrong.

      # Returns true if the round/square/curly brackets of the given node are
      # on different lines, and each item within is on its own line, and the
      # closing bracket is on its own line.
      def multiline?(node)

The closing bracket, ) in your case, is not on its own line.

I noted BTW that you also need the following configuration to reproduce the problem:

Style/BracesAroundHashParameters:
  EnforcedStyle: braces

[brandonweiss]

@jonas054 ❤️