Handle #if clauses inside of switch statements.

Sources/SwiftFormatPrettyPrint/TokenStreamCreator.swift

@@ -640,6 +640,17 @@ fileprivate final class TokenStreamCreator: SyntaxVisitor {
     before(node.leftBrace, tokens: .break(.reset))
     after(node.leftBrace, tokens: .close)
 
+    // An if-configuration clause around a switch-case encloses the case's node, so an
+    // if-configuration clause requires a break here in order to be allowed on a new line.
+    for ifConfigDecl in node.cases.filter({ $0.is(IfConfigDeclSyntax.self) }) {
+      if config.indentSwitchCaseLabels {
+        before(ifConfigDecl.firstToken, tokens: .break(.open))
+        after(ifConfigDecl.lastToken, tokens: .break(.close, size: 0))
+      } else {
+        before(ifConfigDecl.firstToken, tokens: .break(.same))
+      }
+    }
+
     let newlines: NewlineBehavior =
       areBracesCompletelyEmpty(node, contentsKeyPath: \.cases) ? .elective : .soft
     before(node.rightBrace, tokens: .break(.same, size: 0, newlines: newlines))

Tests/SwiftFormatPrettyPrintTests/SwitchStmtTests.swift

@@ -1,3 +1,5 @@
+import SwiftFormatConfiguration
+
 final class SwitchStmtTests: PrettyPrintTestCase {
   func testBasicSwitch() {
     let input =
@@ -332,4 +334,97 @@ final class SwitchStmtTests: PrettyPrintTestCase {
 
     assertPrettyPrintEqual(input: input, expected: expected, linelength: 20)
   }
+
+  func testConditionalCases() {
+    let input =
+      """
+      switch foo {
+      #if CONDITION_A
+      case bar:
+        callForBar()
+      #endif
+      case baz:
+        callForBaz()
+      }
+      switch foo2 {
+      case bar2:
+        callForBar()
+      #if CONDITION_B
+      case baz2:
+        callForBaz()
+      #endif
+      }
+      """
+
+    let expected =
+      """
+      switch foo {
+      #if CONDITION_A
+        case bar:
+          callForBar()
+      #endif
+      case baz:
+        callForBaz()
+      }
+      switch foo2 {
+      case bar2:
+        callForBar()
+      #if CONDITION_B
+        case baz2:
+          callForBaz()
+      #endif
+      }
+
+      """
+
+    assertPrettyPrintEqual(input: input, expected: expected, linelength: 40)
+  }
+
+  func testConditionalCasesIndenting() {
+    let input =
+      """
+      switch foo {
+      #if CONDITION_A
+      case bar:
+        callForBar()
+      #endif
+      case baz:
+        callForBaz()
+      }
+      switch foo2 {
+      case bar2:
+        callForBar()
+      #if CONDITION_B
+      case baz2:
+        callForBaz()
+      #endif
+      }
+      """
+
+    let expected =
+      """
+      switch foo {
+        #if CONDITION_A
+          case bar:
+            callForBar()
+        #endif
+        case baz:
+          callForBaz()
+      }
+      switch foo2 {
+        case bar2:
+          callForBar()
+        #if CONDITION_B
+          case baz2:
+            callForBaz()
+        #endif
+      }
+
+      """
+
+    var configuration = Configuration()
+    configuration.indentSwitchCaseLabels = true
+    assertPrettyPrintEqual(
+      input: input, expected: expected, linelength: 40, configuration: configuration)
+  }
 }