Fix error for trailing newline before end-of-file

Author: kimdv

Sources/SwiftParser/ParseSourceFile.swift

@@ -152,8 +152,9 @@ extension Parser {
     }
 
     let remainingTokens = self.consumeRemainingTokens()
+
     if remainingTokens.isEmpty {
-      return into
+      return R.init(transferTrailingTrivaFromEndOfFileIfPresent(raw: into.raw))!
     }
 
     let existingUnexpected: [RawSyntax]
@@ -166,6 +167,33 @@ extension Parser {
     let unexpected = RawUnexpectedNodesSyntax(elements: existingUnexpected + remainingTokens, arena: self.arena)
 
     let withUnexpected = layout.replacingChild(at: layout.children.count - 1, with: unexpected.raw, arena: self.arena)
-    return R.init(withUnexpected)!
+
+    return R.init(transferTrailingTrivaFromEndOfFileIfPresent(raw: withUnexpected))!
+  }
+
+  /// Parses the end-of-file token and appends its leading trivia to the provided `RawSyntax`.
+  /// - Parameter raw: The raw syntax node to which the leading trivia of the end-of-file token will be appended.
+  /// - Returns: A new `RawSyntax` instance with trailing trivia transferred from the end-of-file token if present, otherwise it will return the raw parameter..
+  private mutating func transferTrailingTrivaFromEndOfFileIfPresent(raw: RawSyntax) -> RawSyntax {
+    guard let endOfFileToken = self.consume(if: .endOfFile),
+      !endOfFileToken.leadingTriviaPieces.isEmpty,
+      let raw = raw.withTrailingTrivia(
+        Trivia(
+          rawPieces: (raw.trailingTriviaPieces ?? []) + endOfFileToken.leadingTriviaPieces
+        ),
+        arena: self.arena
+      )
+    else {
+      return raw
+    }
+
+    return raw
+  }
+}
+
+private extension Trivia {
+  init(rawPieces: [RawTriviaPiece]) {
+    let pieces = rawPieces.map(TriviaPiece.init(raw:))
+    self.init(pieces: pieces)
   }
 }

Sources/SwiftSyntax/Raw/RawSyntax.swift

@@ -302,6 +302,7 @@ extension RawSyntax {
   /// - Parameters:
   ///   - leadingTrivia: The trivia to attach.
   ///   - arena: SyntaxArena to the result node data resides.
+  @_spi(RawSyntax)
   func withLeadingTrivia(_ leadingTrivia: Trivia, arena: SyntaxArena) -> RawSyntax? {
     switch view {
     case .token(let tokenView):
@@ -328,7 +329,8 @@ extension RawSyntax {
   /// - Parameters:
   ///   - trailingTrivia: The trivia to attach.
   ///   - arena: SyntaxArena to the result node data resides.
-  func withTrailingTrivia(_ trailingTrivia: Trivia, arena: SyntaxArena) -> RawSyntax? {
+  @_spi(RawSyntax)
+  public func withTrailingTrivia(_ trailingTrivia: Trivia, arena: SyntaxArena) -> RawSyntax? {
     switch view {
     case .token(let tokenView):
       return .makeMaterializedToken(

Tests/SwiftParserTest/DeclarationTests.swift

@@ -3120,4 +3120,17 @@ final class DeclarationTests: ParserTestCase {
       experimentalFeatures: .nonEscapableTypes
     )
   }
+
+  func testDeclarationEndingWithNewline() {
+    let inputs: [UInt: String] = [
+      #line: "var x = 0\n",
+      #line: "var x = 0 garbage\n",
+      #line: "var x = 0 \n",
+    ]
+
+    for (line, input) in inputs {
+      let decl = DeclSyntax(stringLiteral: input)
+      XCTAssertEqual(decl.description, input, line: line)
+    }
+  }
 }

Tests/SwiftSyntaxMacroExpansionTest/PeerMacroTests.swift

@@ -151,7 +151,7 @@ final class PeerMacroTests: XCTestCase {
           Task {
             completionHandler(await f(a: a, for: b, value))
           }
-        }
+          }
         """,
       macros: ["addCompletionHandler": AddCompletionHandler.self],
       indentationWidth: indentationWidth