False positive for trailing_closure rule with anonymous closure call

[proxi]

New Issue Checklist

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

Bug Report

It is sometimes handy to use anonymous closure as code grouping, e.g.:

menu.addItem({
    let menuItem = NSMenuItem(title: "Blah!")
    return menuItem
}())

When linted with trailing_closure enable, this incorrectly triggers a warning.

Complete output when running SwiftLint, including the stack trace and command used

Bagombo:closure proxi$ swiftlint 
Loading configuration from '.swiftlint.yml'
Linting Swift files in current working directory
Linting 'Closure.swift' (1/1)
Closure.swift:2:5: warning: Trailing Closure Violation: Trailing closure syntax should be used whenever possible. (trailing_closure)
Done linting! Found 1 violation, 0 serious in 1 file.
Bagombo:closure proxi$ 

Environment

• SwiftLint version (run swiftlint version to be sure)? 0.25.1
• Installation method used (Homebrew, CocoaPods, building from source, etc)? CocoaPods
• Paste your configuration file:

opt_in_rules:
    - trailing_closure

• Are you using nested configurations?
  If so, paste their relative paths and respective contents. No
• Which Xcode version are you using (check xcode-select -p)? 9.3
• Do you have a sample that shows the issue? Run echo "[string here]" | swiftlint lint --no-cache --use-stdin --enable-all-rules
  to quickly test if your example is really demonstrating the issue. If your example is more
  complex, you can use swiftlint lint --path [file here] --no-cache --enable-all-rules.

// This triggers a violation:
func foo(_ bar: Int) {
    foo({ return 42 }())
}

[pashcal]

Also looks like a similar bug:
"trailing_closure" is triggering on Dictionary(grouping: list, by: { $0.group }).sorted { $0.key < $1.key }, but not with Dictionary(grouping: list) { $0.group }.sorted { $0.key < $1.key }.
For me, first options is more readable.

[marcelofabri]

@pashcal for future reference: what you're describing is not bug: the rule checks all closures that can be closure.

If you believe the first one is more readable, please open an issue to track adding a configuration to treat it as a special case. Please try to specify the enhancement as a generic case. When should the rule ignore the fact that a closure can be a trailing closure?