Fix indentation issue if trailing trivia contains a newline at the end of an indentation scope

Sources/SwiftBasicFormat/BasicFormat.swift

@@ -594,8 +594,19 @@ open class BasicFormat: SyntaxRewriter {
       trailingTriviaIndentation = anchorPointIndentation
     }
 
-    leadingTrivia = leadingTrivia.indented(indentation: leadingTriviaIndentation, isOnNewline: previousTokenIsStringLiteralEndingInNewline)
-    trailingTrivia = trailingTrivia.indented(indentation: trailingTriviaIndentation, isOnNewline: false)
+    leadingTrivia = leadingTrivia.indented(
+      indentation: leadingTriviaIndentation,
+      isOnNewline: previousTokenIsStringLiteralEndingInNewline || previousTokenWillEndWithNewline
+    )
+    trailingTrivia = trailingTrivia.indented(
+      indentation: trailingTriviaIndentation,
+      isOnNewline: false,
+      // Don't add indentation to the last newline.
+      // Its indentation will be added to the next token's leading trivia, which
+      // might have a different indentation scope than this token (in particular
+      // if this token is a closing brace).
+      addIndentationAfterLastNewline: false
+    )
 
     leadingTrivia = leadingTrivia.trimmingTrailingWhitespaceBeforeNewline(isBeforeNewline: leadingTriviaIsFollowedByNewline)
     trailingTrivia = trailingTrivia.trimmingTrailingWhitespaceBeforeNewline(isBeforeNewline: nextTokenWillStartWithNewline)

Sources/SwiftBasicFormat/Trivia+FormatExtensions.swift

@@ -62,7 +62,20 @@ extension Trivia {
   }
 
   /// Adds `indentation` after every newline in this trivia.
-  func indented(indentation: Trivia, isOnNewline: Bool) -> Trivia {
+  ///
+  /// - Parameters:
+  ///   - indentation: The amount of indentation to add.
+  ///   - isOnNewline: Whether this token starts on a new line.
+  ///     This causes the indentation to get added at the start of the trivia.
+  ///   - addIndentationAfterLastNewline: Whether to add indentation after newline
+  ///     if the newline is the last piece of trivia. Not doing this makes sense
+  ///     if the indentation will get added to the next token's leading trivia
+  ///     via `isOnNewline`.
+  func indented(
+    indentation: Trivia,
+    isOnNewline: Bool,
+    addIndentationAfterLastNewline: Bool = true
+  ) -> Trivia {
     guard !isEmpty else {
       if isOnNewline {
         return indentation
@@ -72,13 +85,13 @@ extension Trivia {
 
     var indentedPieces: [TriviaPiece] = []
     if isOnNewline {
-      indentedPieces.append(contentsOf: indentation)
+      indentedPieces += indentation
     }
 
-    for piece in pieces {
+    for (index, piece) in pieces.enumerated() {
       indentedPieces.append(piece)
-      if piece.isNewline {
-        indentedPieces.append(contentsOf: indentation)
+      if piece.isNewline && !(index == pieces.count - 1 && !addIndentationAfterLastNewline) {
+        indentedPieces += indentation
       }
     }
 

Tests/SwiftBasicFormatTest/BasicFormatTests.swift

@@ -566,4 +566,47 @@ final class BasicFormatTest: XCTestCase {
       """
     assertFormatted(source: source, expected: source)
   }
+
+  func testNewlineInTrailingTriviaAtEndOfIndentationScope() throws {
+    assertFormatted(
+      tree: try FunctionDeclSyntax("func test()") {
+        CodeBlockItemSyntax("Task {\n}\n")
+      },
+      expected: """
+        func test() {
+            Task {
+            }
+        }
+        """
+    )
+
+    assertFormatted(
+      tree: try FunctionDeclSyntax("func test()") {
+        CodeBlockItemSyntax("Task {\n}\n\n")
+      },
+      expected: """
+        func test() {
+            Task {
+            }
+        }
+        """
+    )
+
+    assertFormatted(
+      tree: try FunctionDeclSyntax("func bar()") {
+        try FunctionDeclSyntax("func test()") {
+          CodeBlockItemSyntax("Task {\n}\n")
+        }
+      },
+      expected: """
+        func bar() {
+            func test() {
+                Task {
+                }
+            }
+        }
+        """
+    )
+  }
+
 }