Add support for ignore pattern for LineLength cop

[swalkinshaw]

👋 We generally like and enforce the LineLength cop, but there are certain contexts where it's not ideal.

Proposal

My proposal is an IgnoredPatterns option which is an array of regexps. If any of these match a line, the line length cop is skipped.

Metrics/LineLength:
  Enabled: true
  Max: 120
  IgnoredPatterns:
    - '^\s*test\s.*'

Alternatives

There's two existing ways to deal with this (that I know of):

• comments to disable the cop
• ignore an entire file

Our main use case is ignore line lengths for test/spec descriptions.

Examples:

def test_some_really_long_minitest_test_method_name
end

test 'some really long test description which exceeds length' do
end

It's not ideal to have comments around every test method/description, or to ignore the file entirely.

Solution

I've already made a custom cop that implements this here: https://gist.github.com/swalkinshaw/c540a59b4983b335149c2f6fde69e7b9

I'd be happy to implement this via a PR in the existing LineLength cop if it's wanted.

[bbatsov]

I'm on the fence about this. Typically I just suggest people to allow longer lines in their tests. (you can have different config files in different folders)

I'm curious to hear about thoughts on the subject.

[swalkinshaw]

Yeah I agree it's a slippery slope. Ideally we still want to enforce line length on the test bodies since it's just code and we want to keep it readable. Unfortunately there's just no nice/readable way to make test descriptions multi-line to play by the rules.

So we're left in a weird situation where there are a few legitimate contexts where longer lines should be allowed and they happen consistently enough.

I can only speak for Shopify, but this has come up multiple times with developers asking if there's a way to disable this rule for test/spec descriptions. We have an issue on our styleguide with 35 comments so far about this issue :)

In case this feature doesn't make it in, I have an alternative proposal. I'm perfectly happy making custom cops but right now it's harder since you can't inherit from an existing one.

Please correct me if I'm wrong, but the way all cops are tracked right now via inherited doesn't allow subclassing LineLength for example.

An alternate method to track class descendants might make this more flexible.