New Issue Checklist

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

New rule request

A Function body should not be empty. Otherwise, show a warning.

An empty function, init and deinit can harm readability and lead to confusion because readers need to guess whether it's intentional or not.
Developers should put a comment to explain why the function/ init / deinit body is empty.

SonarLint for Swift and ESLint have the same rule.
SwiftLint can be better by having this rule.

Triggering and Non-Triggering

Triggering:

func f1 () {}

func f2 () {
}

// Comment
func f3 () {}

init() {}

deinit {}

Non-Triggering

func f4 () {
    let s = "xyz"
}

func f5 () { /* Comment*/  }

func f6() {
    // Comment
}

init() { /* comment */ }

deinit { /* comment */ }

Just so you know, this behavior is the same as SonarLint and ESLint.

Should be configurable?

No parameter to configure.

Should be opt-in?

In my opinion, this rule should be "opt-in rule" since there is no consensus, though it's active by default in SonarLint and ESLint.
Got feed back, and change to default.

If this rule makes sense, I will work for this!
Thanks.

Future enhancement

We can implement rules for closures and initializers as well.
But, they should be implemented as separate rules.