Add SwiftFormat void rule (#288)

README.md

@@ -3677,6 +3677,34 @@ _You can enable the following settings in Xcode by running [this script](resourc
 
     </details>
 
+* <a id='void-type'></a>(<a href='#void-type'>link</a>) **Avoid using `()` as a type**. Prefer `Void`.
+
+  <details>
+
+  ```swift
+  // WRONG
+  let result: Result<(), Error>
+
+  // RIGHT
+  let result: Result<Void, Error>
+  ```
+  </details>
+
+* <a id='void-instance'></a>(<a href='#void-instance'>link</a>) **Avoid using `Void()` as an instance of `Void`**. Prefer `()`.
+
+  <details>
+
+  ```swift
+  let completion: (Result<Void, Error>) -> Void 
+
+  // WRONG
+  completion(.success(Void()))
+
+  // RIGHT
+  completion(.success(()))
+  ```
+  </details>
+
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 ## File Organization

Sources/AirbnbSwiftFormatTool/airbnb.swiftformat

@@ -109,6 +109,7 @@
 --rules preferForLoop
 --rules conditionalAssignment
 --rules wrapMultilineConditionalAssignment
+--rules void
 --rules blankLineAfterSwitchCase
 --rules consistentSwitchCaseSpacing
 --rules semicolons

Sources/AirbnbSwiftFormatTool/swiftlint.yml

@@ -6,7 +6,6 @@ only_rules:
   - legacy_constructor
   - legacy_nsgeometry_functions
   - unused_optional_binding
-  - void_return # TODO: Replace with SwiftFormat void rule
   - unowned_variable_capture
   - custom_rules