False positive in force_unwrapping when returning collection from function

[marcelofabri]

New Issue Checklist

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

Bug Report

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

$ echo "func foo() -> [AnyHashable: Any]\!" | swiftlint lint --no-cache --use-stdin --enable-all-rules 
Loading configuration from '.swiftlint.yml'
<nopath>:1:33: warning: Force Unwrapping Violation: Force unwrapping should be avoided. (force_unwrapping)

Environment

• SwiftLint version (run swiftlint version to be sure)? 0.24.2
• Installation method used (Homebrew, CocoaPods, building from source, etc)? Homebrew
• Paste your configuration file:

opt_in_rules:
  - force_unwrapping

• 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)? 9.2
• 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() -> [AnyHashable: Any]!
func bar() -> [Int]!

[Coeur]

If the rule force_unwrapping doesn't trigger a violation for return types, then I can declare:

extension Optional {
    var forceUnwrapped: Wrapped! {
        return self
    }
}

Then I replace all the foo! with foo.forceUnwrapped and SwiftLint will never trigger the force_unwrapping rule.