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False positive for `trailing_closure` rule with anonymous closure call #2159

proxi opened this Issue Apr 17, 2018 · 2 comments


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proxi commented Apr 17, 2018

New Issue Checklist

Bug Report

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

    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$ 


  • 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:
    - 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 }())

@marcelofabri marcelofabri added the bug label Apr 17, 2018


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Pashcal commented Oct 10, 2018

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


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marcelofabri commented Jan 19, 2019

@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?

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