Add rule to insert a blank line following a switch case with a multi-…

…line body
airbnb · Feb 2, 2024 · 369bee9 · 369bee9
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diff --git a/README.md b/README.md
@@ -1240,6 +1240,161 @@ _You can enable the following settings in Xcode by running [this script](resourc
 
   </details>
 
+* <a id='blank-line-after-multiline-switch-case'></a>(<a href='#blank-line-after-multiline-switch-case'>link</a>) **Insert a blank line following a switch case with a multi-line body.** For consistency within a switch statement, if any case has a multi-line body then all cases should include a trailing blank line. The last switch case doesn't need a blank line, since it is already followed by a closing brace. [![SwiftFormat: blankLineAfterMultilineSwitchCase](https://img.shields.io/badge/SwiftFormat-blankLineAfterMultilineSwitchCase-7B0051.svg)](https://github.com/nicklockwood/SwiftFormat/blob/master/Rules.md#blankLineAfterMultilineSwitchCase) [![SwiftFormat: consistentSwitchStatementSpacing](https://img.shields.io/badge/SwiftFormat-consistentSwitchStatementSpacing-7B0051.svg)](https://github.com/nicklockwood/SwiftFormat/blob/master/Rules.md#consistentSwitchStatementSpacing)
+
+  <details>
+
+  #### Why?
+
+  Like with [declarations in a file](https://github.com/airbnb/swift#newline-between-scope-siblings), inserting a blank line between scopes makes them easier to visually differentiate.
+
+  Switch statements with multi-lines lines can become visiually busy and cramped without blank lines between the cases. In this example, all of the cases start to bleed together, making it more difficult to read the code at a glance:
+
+  ```swift
+  func handle(_ action: SpaceshipAction) {
+    switch action {
+    case .engageWarpDrive:
+      navigationComputer.destination = targetedDestination
+      warpDrive.spinUp()
+      warpDrive.activate()
+    case .enableArtificialGravity:
+      artificialGravityEngine.enable(strength: .oneG)
+    case .scanPlanet(let planet):
+      scanner.target = planet
+      scanner.scanAtmosphere()
+      scanner.scanBiosphere()
+      scanner.scanForArtificialLife()
+    case .handleIncomingEnergyBlast:
+      energyShields.engage()
+    }
+  }
+  ```
+
+  Blank lines between the individual cases make the switch statement much easier to read:
+
+  ```swift
+  func handle(_ action: SpaceshipAction) {
+    switch action {
+    case .engageWarpDrive:
+      navigationComputer.destination = targetedDestination
+      warpDrive.spinUp()
+      warpDrive.activate()
+
+    case .enableArtificialGravity:
+      artificialGravityEngine.enable(strength: .oneG)
+
+    case .scanPlanet(let planet):
+      scanner.target = planet
+      scanner.scanAtmosphere()
+      scanner.scanBiosphere()
+      scanner.scanForArtificialLife()
+
+    case .handleIncomingEnergyBlast:
+      energyShields.engage()
+    }
+  }
+  ```
+
+  #### Examples
+
+  ```swift
+  // WRONG. These switch cases should be followed by a blank line.
+  func handle(_ action: SpaceshipAction) {
+    switch action {
+    case .engageWarpDrive:
+      navigationComputer.destination = targetedDestination
+      warpDrive.spinUp()
+      warpDrive.activate()
+    case .enableArtificialGravity:
+      artificialGravityEngine.enable(strength: .oneG)
+    case .scanPlanet(let planet):
+      scanner.target = planet
+      scanner.scanAtmosphere()
+      scanner.scanBiosphere()
+      scanner.scanForArtificialLife()
+    case .handleIncomingEnergyBlast:
+      energyShields.engage()
+    }
+  }
+
+  // WRONG. While the `.enableArtificialGravity` case isn't multi-line, the other cases are.
+  // For consistency, it should also include a trailing blank line.
+  func handle(_ action: SpaceshipAction) {
+    switch action {
+    case .engageWarpDrive:
+      navigationComputer.destination = targetedDestination
+      warpDrive.spinUp()
+      warpDrive.activate()
+
+    case .enableArtificialGravity:
+      artificialGravityEngine.enable(strength: .oneG)
+    case .scanPlanet(let planet):
+      scanner.target = planet
+      scanner.scanAtmosphere()
+      scanner.scanBiosphere()
+      scanner.scanForArtificialLife()
+
+    case .handleIncomingEnergyBlast:
+      energyShields.engage()
+    }
+  }
+
+  // RIGHT. All of the cases have a trailing blank line.
+  func handle(_ action: SpaceshipAction) {
+    switch action {
+    case .engageWarpDrive:
+      navigationComputer.destination = targetedDestination
+      warpDrive.spinUp()
+      warpDrive.activate()
+
+    case .enableArtificialGravity:
+      artificialGravityEngine.enable(strength: .oneG)
+
+    case .scanPlanet(let planet):
+      scanner.target = planet
+      scanner.scanAtmosphere()
+      scanner.scanBiosphere()
+      scanner.scanForArtificialLife()
+
+    case .handleIncomingEnergyBlast:
+      energyShields.engage()
+    }
+  }
+
+  // RIGHT. Since none of the cases are multi-line, blank lines are not required.
+  func handle(_ action: SpaceshipAction) {
+    switch action {
+    case .engageWarpDrive:
+        warpDrive.engage()
+    case .enableArtificialGravity:
+        artificialGravityEngine.enable(strength: .oneG)
+    case .scanPlanet(let planet):
+        scanner.scan(planet)
+    case .handleIncomingEnergyBlast:
+        energyShields.engage()
+    }
+  }
+
+  // ALSO RIGHT. Blank lines are still permitted after single-line switch cases if it helps with readability.
+  func handle(_ action: SpaceshipAction) {
+    switch action {
+    case .engageWarpDrive:
+        warpDrive.engage()
+
+    case .enableArtificialGravity:
+        artificialGravityEngine.enable(strength: .oneG)
+
+    case .scanPlanet(let planet):
+        scanner.scan(planet)
+
+    case .handleIncomingEnergyBlast:
+        energyShields.engage()
+    }
+  }
+  ```
+
+  </details>
+
 * <a id='wrap-guard-else'></a>(<a href='#wrap-guard-else'>link</a>) **Add a line break before the `else` keyword in a multi-line guard statement.** For single-line guard statements, keep the `else` keyword on the same line as the `guard` keyword. The open brace should immediately follow the `else` keyword. [![SwiftFormat: elseOnSameLine](https://img.shields.io/badge/SwiftFormat-elseOnSameLine-7B0051.svg)](https://github.com/nicklockwood/SwiftFormat/blob/master/Rules.md#elseOnSameLine)
 
   <details>

diff --git a/Sources/AirbnbSwiftFormatTool/airbnb.swiftformat b/Sources/AirbnbSwiftFormatTool/airbnb.swiftformat
@@ -97,3 +97,5 @@
 --rules preferForLoop
 --rules conditionalAssignment
 --rules wrapMultilineConditionalAssignment
+--rules blankLineAfterMultilineSwitchCase
+--rules consistentSwitchStatementSpacing