Add emptyExtension rule

README.md

@@ -4002,6 +4002,25 @@ _You can enable the following settings in Xcode by running [this script](resourc
   ```
 
   </details>
+
+* <a id='remove-empty-extensions'></a>(<a href='#remove-empty-extensions'>link</a>) **Remove empty extensions that define no properties, functions, or conformances.** [![SwiftFormat: emptyExtension](https://img.shields.io/badge/SwiftFormat-emptyExtension-008489.svg)](https://github.com/nicklockwood/SwiftFormat/blob/master/Rules.md#emptyExtension)
+
+  <details>
+
+  #### Why?
+  Improves readability since the code has no effect and should be removed for clarity.
+
+  ```swift
+  // WRONG: The first extension is empty and redundant.
+  extension Planet {}
+
+  extension Planet: Equatable {}
+
+  // RIGHT: Empty extensions that add a protocol conformance aren't redundant.
+  extension Planet: Equatable {}
+  ```
+
+  </details>
 
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Sources/AirbnbSwiftFormatTool/airbnb.swiftformat

@@ -108,4 +108,5 @@
 --rules consistentSwitchCaseSpacing
 --rules semicolons
 --rules propertyType
---rules blankLinesBetweenChainedFunctions
+--rules blankLinesBetweenChainedFunctions
+--rules emptyExtension