multiline_arguments_brackets reports false positives with calls whose one parameter spans multiple lines

[noahsark769]

New Issue Checklist

• Updated SwiftLint to the latest version
• I searched for existing GitHub issues

Describe the bug

The multiline_arguments_brackets rule produces what I would categorize as a false positive in calls which have a single argument with a multiline value. For example, multiline_arguments_brackets is triggered on the following examples:

public final class Logger {
    public static let shared = Logger(outputs: [
        OSLoggerOutput(),
        ErrorLoggerOutput()
    ])
}

let errors = try self.download([
    (description: description, priority: priority),
])

return SignalProducer({ observer, _ in
    observer.sendCompleted()
}).onMainQueue()

I'm not 100% sure that this is not intentional, but it seems to me that these cases should pass the "smell test" of multiline_arguments_brackets, since the idea with this rule is to prevent argument brackets from being mis-aligned with the actual passed arguments. I think that if return SignalProducer({ observer, _ in observer.sendCompleted() }) passes the rule, then

return SignalProducer({ observer, _ in
    observer.sendCompleted()
}).onMainQueue()

should also pass the rule.

None of these cases are noted in the triggering or non-triggering examples at https://realm.github.io/SwiftLint/multiline_arguments_brackets.html, though a few non-triggering examples are similar:

foo { param1, param2 in
    print("hello world")
}

AlertViewModel.AlertAction(title: "some title", style: .default) {
    AlertManager.shared.presentNextDebugAlert()
}

I'd further argue that the currently triggering cases I listed above match the style of these non-triggering cases.

I'm looking for feedback here on whether this is intentional, and if it seems to the maintainers that the rule should cover these cases then I'm happy to take a crack at implementing it 😄

Environment

• SwiftLint version (run swiftlint version to be sure)? 0.39.1

• Installation method used (Homebrew, CocoaPods, building from source, etc)? Cocoapods

• Paste your configuration file: I can provide a full configuration file if necessary, but this should be fairly easy to reproduce

• Are you using nested configurations? No

• Which Xcode version are you using (check xcodebuild -version)? Xcode 11.2.1 Build version 11B500

• Do you have a sample that shows the issue? Yes:

echo "
public final class Logger {

    /// Default logger instance currently used globally.
    public static let shared = Logger(outputs: [
        OSLoggerOutput(),
        BugsnagLoggerOutput(),
        FileLoggerOutput(),
    ])
}
" | ./Pods/SwiftLint/swiftlint  lint --no-cache --use-stdin --enable-all-rules

The above triggers multiline_arguments_brackets

[noahsark769]

I noticed that there's a similar problem with multiline_parameters_brackets and default arguments: if your default argument spans multiple lines, the regex checks in MultilineParametersBracketsRule succeed and report violations. For example, the following fails multiline_parameters_brackets:

func foo(a: [Int] = [
    1
])

[noahsark769]

I believe I've figured out a good way to fix this - we're currently assuming the call has newlines if any newlines exist in the body, when in fact the correct way is to check that the number of newlines in the body is more than the number of combined newlines in the actual argument bodies. Will try and get a pull request up for this soon.

[noahsark769]

Put up a PR over at #3171, happy to discuss. Thanks!

[marcelofabri]

Fixed in #3171