Update trailing commas rule to apply to all multi-element comma-separated lists (#323)

#### Summary

This PR updates the trailing commas rule to apply to all comma-separated
lists, including function calls and function declarations.

```swift
let terrestrialPlanets = [
  mercury,
  venus,
  earth,
  mars,
]

func buildSolarSystem(
  innerPlanets: [Planet],
  outerPlanets: [Planet],
) { ... }

buildSolarSystem(
  innertPlanets: terrestrialPlanets,
  outerPlanets: gasGiants,
)
```

This PR also refines the rule to omit the trailing comma if the list
only contains a single element. We feel this is especially the right
choice in function calls with only a single argument, where the trailing
commas adds unnecessary noise:

```swift
// WRONG
let planetsWithLife = [
  earth,
]

func buildSolarSystem(
  _ planets: [Planet],
)

buildSolarSystem(
  terrestrialPlanets + gasGiants,
)

// RIGHT
let planetsWithLife = [
  earth
]

func buildSolarSystem(
  _ planets: [Planet]
) { ... }

buildSolarSystem(
  terrestrialPlanets + gasGiants
)
```

<!--- required --->

Author: calda

Package.swift

@@ -5,10 +5,10 @@ let package = Package(
   name: "AirbnbSwift",
   platforms: [.macOS(.v10_13)],
   products: [
-    .plugin(name: "FormatSwift", targets: ["FormatSwift"]),
+    .plugin(name: "FormatSwift", targets: ["FormatSwift"])
   ],
   dependencies: [
-    .package(url: "https://github.com/apple/swift-argument-parser", from: "1.0.3"),
+    .package(url: "https://github.com/apple/swift-argument-parser", from: "1.0.3")
   ],
   targets: [
     .plugin(
@@ -19,7 +19,7 @@ let package = Package(
           description: "Formats Swift source files according to the Airbnb Swift Style Guide"
         ),
         permissions: [
-          .writeToPackageDirectory(reason: "Format Swift source files"),
+          .writeToPackageDirectory(reason: "Format Swift source files")
         ]
       ),
       dependencies: [
@@ -32,7 +32,7 @@ let package = Package(
     .executableTarget(
       name: "AirbnbSwiftFormatTool",
       dependencies: [
-        .product(name: "ArgumentParser", package: "swift-argument-parser"),
+        .product(name: "ArgumentParser", package: "swift-argument-parser")
       ],
       resources: [
         .process("airbnb.swiftformat"),

Plugins/FormatSwift/Plugin.swift

@@ -209,7 +209,7 @@ extension Package {
     guard let projectDirectory = URL(string: directory.string) else { return [] }
 
     var supportedSwiftVersions = [
-      SwiftVersion(major: toolsVersion.major, minor: toolsVersion.minor),
+      SwiftVersion(major: toolsVersion.major, minor: toolsVersion.minor)
     ]
 
     // Look for all of the package manifest files in the directory root

README.md

@@ -526,26 +526,78 @@ _You can enable the following settings in Xcode by running [this script](resourc
 
   </details>
 
-* <a id='trailing-comma-array'></a>(<a href='#trailing-comma-array'>link</a>) **Add a trailing comma on the last element of a multi-line array.** [![SwiftFormat: trailingCommas](https://img.shields.io/badge/SwiftFormat-trailingCommas-7B0051.svg)](https://github.com/nicklockwood/SwiftFormat/blob/main/Rules.md#trailingCommas)
+* <a id='trailing-commas'></a>(<a href='#trailing-commas'>link</a>) **Add a trailing comma after the last element of multi-line, multi-element comma-separated lists.* This includes arrays, dictionaries, function declarations, function calls, etc. Don't include a trailing comma if the list spans only a single line, or contains only a single element. [![SwiftFormat: trailingCommas](https://img.shields.io/badge/SwiftFormat-trailingCommas-7B0051.svg)](https://github.com/nicklockwood/SwiftFormat/blob/main/Rules.md#trailingCommas)
 
   <details>
 
   ```swift
   // WRONG
-  let rowContent = [
-    listingUrgencyDatesRowContent(),
-    listingUrgencyBookedRowContent(),
-    listingUrgencyBookedShortRowContent()
+  let terrestrialPlanets = [
+    mercury,
+    venus,
+    earth,
+    mars
   ]
 
+  func buildSolarSystem(
+    innerPlanets: [Planet],
+    outerPlanets: [Planet]
+  ) { ... }
+
+  buildSolarSystem(
+    innertPlanets: terrestrialPlanets,
+    outerPlanets: gasGiants
+  )
+
   // RIGHT
-  let rowContent = [
-    listingUrgencyDatesRowContent(),
-    listingUrgencyBookedRowContent(),
-    listingUrgencyBookedShortRowContent(),
+  let terrestrialPlanets = [
+    mercury,
+    venus,
+    earth,
+    mars,
+  ]
+
+  func buildSolarSystem(
+    innerPlanets: [Planet],
+    outerPlanets: [Planet],
+  ) { ... }
+
+  buildSolarSystem(
+    innertPlanets: terrestrialPlanets,
+    outerPlanets: gasGiants,
+  )
+  ```
+
+  ```swift
+  // WRONG: Omit the trailing comma in single-element lists.
+  let planetsWithLife = [
+    earth,
   ]
+
+  func buildSolarSystem(
+    _ planets: [Planet],
+  )
+
+  buildSolarSystem(
+    terrestrialPlanets + gasGiants,
+  )
+
+  // RIGHT
+  let planetsWithLife = [
+    earth
+  ]
+
+  func buildSolarSystem(
+    _ planets: [Planet]
+  ) { ... }
+
+  buildSolarSystem(
+    terrestrialPlanets + gasGiants
+  )
   ```
 
+  </details>
+
 * <a id='no-space-inside-collection-brackets'></a>(<a href='#no-space-inside-brackets'>link</a>) **There should be no spaces inside the brackets of collection literals.** [![SwiftFormat: spaceInsideBrackets](https://img.shields.io/badge/SwiftFormat-spaceInsideBrackets-7B0051.svg)](https://github.com/nicklockwood/SwiftFormat/blob/main/Rules.md#spaceInsideBrackets)
 
   <details>

Sources/AirbnbSwiftFormatTool/airbnb.swiftformat

@@ -2,11 +2,11 @@
 --exclude Carthage,Pods,.build
 
 # options
---swift-version 6.0
+--swift-version 6.1
 --language-mode 5
 --self remove # redundantSelf
 --import-grouping testable-bottom # sortedImports
---trailing-commas always # trailingCommas
+--trailing-commas multi-element-lists # trailingCommas
 --trim-whitespace always # trailingSpace
 --indent 2 #indent
 --ifdef no-indent #indent