stdout output contains duplicate content when autocorrecting vertical whitespace

[onelittlefish]

New Issue Checklist

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

Describe the bug

I'm hoping to make use of https://github.com/realm/SwiftLint/pull/4132 (stdin/stdout). Autocorrecting vertical whitespace (vertical_whitespace, vertical_whitespace_closing_braces, and vertical_whitespace_opening_braces) seems to duplicate the file content in the output.

Test.swift:

class Test {
    let x : String = "test"


}

Output:

$ cat Test.swift | swiftlint --fix --use-stdin --enable-all-rules
class Test {
    let x: String = "test"


}

class Test {
    let x : String = "test"

}

class Test {
    let x : String = "test"
}

Done correcting 1 file!

The issue does not occur if the vertical_whitespace, vertical_whitespace_closing_braces, and vertical_whitespace_opening_braces rules are excluded.

.swiftlint-fix.yml:

disabled_rules:
  - vertical_whitespace
  - vertical_whitespace_closing_braces
  - vertical_whitespace_opening_braces

Output:

$ cat Test.swift | swiftlint --fix --use-stdin --config .swiftlint-fix.yml         
class Test {
    let x: String = "test"


}

Done correcting 1 file!

Environment

• SwiftLint version (run swiftlint version to be sure)? 0.49.1
• Installation method used (Homebrew, CocoaPods, building from source, etc)? SwiftLint.pkg
• Are you using nested configurations? No
• Which Xcode version are you using (check xcodebuild -version)? 13.3.1 (13E500a)

[SimplyDanny]

This behavior can be observed with all rules writing directly to the file when correcting. It's not only about the vertical_whitespace* rules. They perform the fix and immediately write the result back to the file. If the file is stdout we notice the different writes as separate outputs.