Fix trivia transfer bugs for freestanding expression macros

There were two bugs in the way we transferred trivia from the original macro expansion expression to the expanded expression.

1. We were attaching the stripped leading trivia to the end of the node
2. We weren’t resetting the `lineContainedComment` and `lineContainedNonWhitespaceNonComment` variables when seeing a newline in a comment-only line

(1) is easy to fix.
For (2), I just remove the entire comment-handling logic because it didn’t match what “Inline Macro” was doing anyway.

rdar://113639097

Author: ahoppen

Sources/SwiftSyntaxMacroExpansion/IndentationUtils.swift

@@ -85,6 +85,13 @@ extension Trivia {
     }
     return Trivia(pieces: resultPieces)
   }
+
+  /// Remove all indentation from the last line of this trivia
+  var removingIndentationOnLastLine: Trivia {
+    let lastNewlineIndex = pieces.lastIndex(where: \.isNewline) ?? pieces.startIndex
+
+    return Trivia(pieces: pieces[..<lastNewlineIndex]) + Trivia(pieces: pieces[lastNewlineIndex...]).removingIndentation
+  }
 }
 
 extension SyntaxProtocol {

Sources/SwiftSyntaxMacroExpansion/MacroSystem.swift

@@ -66,7 +66,7 @@ private func expandFreestandingMemberDeclList(
   let indentedSource =
     expanded
     .indented(by: node.indentationOfFirstLine)
-    .wrappingInNonCommentTrivia(from: node)
+    .wrappingInTrivia(from: node)
   return "\(raw: indentedSource)"
 }
 
@@ -94,7 +94,7 @@ private func expandFreestandingCodeItemList(
   let indentedSource =
     expanded
     .indented(by: node.indentationOfFirstLine)
-    .wrappingInNonCommentTrivia(from: node)
+    .wrappingInTrivia(from: node)
   return "\(raw: indentedSource)"
 }
 
@@ -119,7 +119,7 @@ private func expandFreestandingExpr(
   let indentedSource =
     expanded
     .indented(by: node.indentationOfFirstLine)
-    .wrappingInNonCommentTrivia(from: node)
+    .wrappingInTrivia(from: node)
   return "\(raw: indentedSource)"
 }
 
@@ -947,17 +947,18 @@ private extension AccessorBlockSyntax {
 }
 
 private extension String {
-  /// Add any non-comment trivia from `node` before/after this string.
+  /// Add any trivia from `node` before/after this string.
   ///
-  /// We need to do this because the macro is responsible for copying trivia
-  /// from the freestanding macro to the generated declaration.
-  ///
-  /// Essentially, what we want to keep any empty newlines in front of the
-  /// freestanding macro that separate it from the previous declarations.
-  func wrappingInNonCommentTrivia(from node: some SyntaxProtocol) -> String {
-    return node.leadingTrivia.removingComments.removingIndentation.description
+  /// We need to do this because we are replacing the entire macro expansion
+  /// declaration / expression with the expanded source but semantically, the
+  /// user should think about it as just replacing the `#...` expression without
+  /// any trivia.
+  func wrappingInTrivia(from node: some SyntaxProtocol) -> String {
+    // We need to remove the indentation from the last line because the macro
+    // expansion buffer already contains the indentation.
+    return node.leadingTrivia.removingIndentationOnLastLine.description
       + self
-      + node.leadingTrivia.removingComments.removingIndentation.description
+      + node.trailingTrivia.description
   }
 }
 
@@ -972,37 +973,3 @@ private extension SyntaxProtocol {
     return self.detached
   }
 }
-
-private extension Trivia {
-  /// Drop all comments from the trivia.
-  ///
-  /// If a comment is the only entry on a line, drop the entire line instead of
-  /// leaving an empty line.
-  var removingComments: Trivia {
-    var result: [TriviaPiece] = []
-
-    var lineContainedComment = false
-    var lineContainedNonWhitespaceNonComment = false
-    for piece in self.pieces {
-      switch piece {
-      case .spaces, .tabs:
-        result.append(piece)
-      case .backslashes, .formfeeds, .pounds, .unexpectedText, .verticalTabs:
-        lineContainedNonWhitespaceNonComment = true
-        result.append(piece)
-      case .blockComment, .docBlockComment, .docLineComment, .lineComment:
-        lineContainedComment = true
-      case .carriageReturns, .carriageReturnLineFeeds, .newlines:
-        if lineContainedComment && !lineContainedNonWhitespaceNonComment {
-          continue
-        } else {
-          result.append(piece)
-        }
-        lineContainedComment = false
-        lineContainedNonWhitespaceNonComment = false
-      }
-    }
-
-    return Trivia(pieces: result)
-  }
-}

Tests/SwiftSyntaxMacroExpansionTest/MacroSystemTests.swift

@@ -701,6 +701,25 @@ final class MacroSystemTests: XCTestCase {
     )
   }
 
+  func testTriviaTransferOnExpressionMacro() {
+    assertMacroExpansion(
+      """
+      // Ignore me
+      \t
+      // Capture me
+      #stringify(x)
+      """,
+      expandedSource: """
+        // Ignore me
+        \t
+        // Capture me
+        (x, "x")
+        """,
+      macros: testMacros,
+      indentationWidth: indentationWidth
+    )
+  }
+
   func testCommentsOnExpressionMacro() {
     assertMacroExpansion(
       """
@@ -709,7 +728,7 @@ final class MacroSystemTests: XCTestCase {
       """,
       expandedSource: """
         let b = 
-        (x + y, "x + y")
+        /*leading */ (x + y, "x + y") /*trailing*/
         """,
       macros: testMacros,
       indentationWidth: indentationWidth
@@ -1441,10 +1460,11 @@ final class MacroSystemTests: XCTestCase {
       ) /* trailing comment */
       """,
       expandedSource: """
+        // some comment
         func foo() {
         }
         func bar() {
-        }
+        } /* trailing comment */
         """,
       macros: ["decls": DeclsFromStringsMacro.self],
       indentationWidth: indentationWidth
@@ -1464,10 +1484,11 @@ final class MacroSystemTests: XCTestCase {
       """,
       expandedSource: """
         struct Foo {
+          // some comment
           func foo() {
           }
           func bar() {
-          }
+          } /* trailing comment */
         }
         """,
       macros: ["decls": DeclsFromStringsMacro.self],