Merge pull request swiftlang#25067 from ikesyo/avoid-fallthrough-where-appropriate

[gardening] Avoid fallthrough where appropriate (for readability/understandability)

Author: ikesyo

stdlib/public/Darwin/Foundation/IndexPath.swift

@@ -218,8 +218,8 @@ public struct IndexPath : ReferenceConvertible, Equatable, Hashable, MutableColl
                     }
                 case .single(let index):
                     switch (range.lowerBound, range.upperBound) {
-                    case (0, 0): fallthrough
-                    case (1, 1):
+                    case (0, 0),
+                         (1, 1):
                         return .empty
                     case (0, 1):
                         return .single(index)
@@ -228,11 +228,9 @@ public struct IndexPath : ReferenceConvertible, Equatable, Hashable, MutableColl
                     }
                 case .pair(let first, let second):
                     switch (range.lowerBound, range.upperBound) {
-                    case (0, 0):
-                        fallthrough
-                    case (1, 1):
-                        fallthrough
-                    case (2, 2):
+                    case (0, 0),
+                         (1, 1),
+                         (2, 2):
                         return .empty
                     case (0, 1):
                         return .single(first)
@@ -264,23 +262,19 @@ public struct IndexPath : ReferenceConvertible, Equatable, Hashable, MutableColl
                     self = newValue
                 case .single(let index):
                     switch (range.lowerBound, range.upperBound, newValue) {
-                    case (0, 0, .empty):
-                        fallthrough
-                    case (1, 1, .empty):
+                    case (0, 0, .empty),
+                         (1, 1, .empty):
                         break
                     case (0, 0, .single(let other)):
                         self = .pair(other, index)
                     case (0, 0, .pair(let first, let second)):
                         self = .array([first, second, index])
                     case (0, 0, .array(let other)):
                         self = .array(other + [index])
-                    case (0, 1, .empty):
-                        fallthrough
-                    case (0, 1, .single):
-                        fallthrough
-                    case (0, 1, .pair):
-                        fallthrough
-                    case (0, 1, .array):
+                    case (0, 1, .empty),
+                         (0, 1, .single),
+                         (0, 1, .pair),
+                         (0, 1, .array):
                         self = newValue
                     case (1, 1, .single(let other)):
                         self = .pair(index, other)

stdlib/public/core/StringStorage.swift

@@ -72,9 +72,8 @@ extension _AbstractStringStorage {
     _ outputPtr: UnsafeMutablePointer<UInt8>, _ maxLength: Int, _ encoding: UInt
   ) -> Int8 {
     switch (encoding, isASCII) {
-    case (_cocoaASCIIEncoding, true):
-      fallthrough
-    case (_cocoaUTF8Encoding, _):
+    case (_cocoaASCIIEncoding, true),
+         (_cocoaUTF8Encoding, _):
       guard maxLength >= count + 1 else { return 0 }
       outputPtr.initialize(from: start, count: count)
       outputPtr[count] = 0
@@ -88,9 +87,8 @@ extension _AbstractStringStorage {
   @_effects(readonly)
   internal func _cString(encoding: UInt) -> UnsafePointer<UInt8>? {
     switch (encoding, isASCII) {
-    case (_cocoaASCIIEncoding, true):
-      fallthrough
-    case (_cocoaUTF8Encoding, _):
+    case (_cocoaASCIIEncoding, true),
+         (_cocoaUTF8Encoding, _):
       return start
     default:
       return _cocoaCStringUsingEncodingTrampoline(self, encoding)