Add support for re-indenting block comments.

Sources/SwiftFormat/PrettyPrint/Comment.swift

@@ -58,9 +58,12 @@ struct Comment {
   let kind: Kind
   var text: [String]
   var length: Int
+  // what was the leading indentation, if any, that preceded this comment?
+  var leadingIndent: Indent?
 
-  init(kind: Kind, text: String) {
+  init(kind: Kind, leadingIndent: Indent?, text: String) {
     self.kind = kind
+    self.leadingIndent = leadingIndent
 
     switch kind {
     case .line, .docLine:
@@ -93,6 +96,25 @@ struct Comment {
       return kind.prefix + trimmedLines.joined(separator: separator)
     case .block, .docBlock:
       let separator = "\n"
+
+      // if all the lines after the first matching leadingIndent, replace that prefix with the
+      // current indentation level
+      if let leadingIndent {
+        let rest = self.text.dropFirst()
+
+        let hasLeading = rest.allSatisfy {
+          let result = $0.hasPrefix(leadingIndent.text) || $0.isEmpty
+          return result
+        }
+        if hasLeading, let first = self.text.first, !rest.isEmpty {
+          let restStr = rest.map {
+            let stripped = $0.dropFirst(leadingIndent.text.count)
+            return indent.indentation() + stripped
+          }.joined(separator: separator)
+          return kind.prefix + first + separator + restStr + "*/"
+        }
+      }
+
       return kind.prefix + self.text.joined(separator: separator) + "*/"
     }
   }

Sources/SwiftFormat/PrettyPrint/TokenStreamCreator.swift

@@ -3194,7 +3194,7 @@ fileprivate final class TokenStreamCreator: SyntaxVisitor {
         true,
         [
           .space(size: config.spacesBeforeEndOfLineComments, flexible: true),
-          .comment(Comment(kind: .line, text: text), wasEndOfLine: true),
+          .comment(Comment(kind: .line, leadingIndent: nil, text: text), wasEndOfLine: true),
           // There must be a break with a soft newline after the comment, but it's impossible to
           // know which kind of break must be used. Adding this newline is deferred until the
           // comment is added to the token stream.
@@ -3205,7 +3205,7 @@ fileprivate final class TokenStreamCreator: SyntaxVisitor {
         false,
         [
           .space(size: 1, flexible: true),
-          .comment(Comment(kind: .block, text: text), wasEndOfLine: false),
+          .comment(Comment(kind: .block, leadingIndent: nil, text: text), wasEndOfLine: false),
           // We place a size-0 break after the comment to allow a discretionary newline after
           // the comment if the user places one here but the comment is otherwise adjacent to a
           // text token.
@@ -3294,24 +3294,29 @@ fileprivate final class TokenStreamCreator: SyntaxVisitor {
     // example, even if discretionary newlines are discarded). This is the case when the preceding
     // trivia was a line comment or garbage text.
     var requiresNextNewline = false
+    // Tracking whether or not the last piece was leading indentation. A newline is considered
+    // a 0-space indentation; used for nesting/un-nesting block comments during formatting.
+    var leadingIndent: Indent? = nil
 
     for (index, piece) in trivia.enumerated() {
       if let cutoff = cutoffIndex, index == cutoff { break }
+
       switch piece {
       case .lineComment(let text):
         if index > 0 || isStartOfFile {
           generateEnableFormattingIfNecessary(position ..< position + piece.sourceLength)
-          appendToken(.comment(Comment(kind: .line, text: text), wasEndOfLine: false))
+          appendToken(.comment(Comment(kind: .line, leadingIndent: leadingIndent, text: text), wasEndOfLine: false))
           generateDisableFormattingIfNecessary(position + piece.sourceLength)
           appendNewlines(.soft)
           isStartOfFile = false
         }
         requiresNextNewline = true
+        leadingIndent = nil
 
       case .blockComment(let text):
         if index > 0 || isStartOfFile {
           generateEnableFormattingIfNecessary(position ..< position + piece.sourceLength)
-          appendToken(.comment(Comment(kind: .block, text: text), wasEndOfLine: false))
+          appendToken(.comment(Comment(kind: .block, leadingIndent: leadingIndent, text: text), wasEndOfLine: false))
           generateDisableFormattingIfNecessary(position + piece.sourceLength)
           // There is always a break after the comment to allow a discretionary newline after it.
           var breakSize = 0
@@ -3325,24 +3330,28 @@ fileprivate final class TokenStreamCreator: SyntaxVisitor {
           isStartOfFile = false
         }
         requiresNextNewline = false
+        leadingIndent = nil
 
       case .docLineComment(let text):
         generateEnableFormattingIfNecessary(position ..< position + piece.sourceLength)
-        appendToken(.comment(Comment(kind: .docLine, text: text), wasEndOfLine: false))
+        appendToken(.comment(Comment(kind: .docLine, leadingIndent: leadingIndent, text: text), wasEndOfLine: false))
         generateDisableFormattingIfNecessary(position + piece.sourceLength)
         appendNewlines(.soft)
         isStartOfFile = false
         requiresNextNewline = true
+        leadingIndent = nil
 
       case .docBlockComment(let text):
         generateEnableFormattingIfNecessary(position ..< position + piece.sourceLength)
-        appendToken(.comment(Comment(kind: .docBlock, text: text), wasEndOfLine: false))
+        appendToken(.comment(Comment(kind: .docBlock, leadingIndent: leadingIndent, text: text), wasEndOfLine: false))
         generateDisableFormattingIfNecessary(position + piece.sourceLength)
         appendNewlines(.soft)
         isStartOfFile = false
         requiresNextNewline = false
+        leadingIndent = nil
 
       case .newlines(let count), .carriageReturns(let count), .carriageReturnLineFeeds(let count):
+        leadingIndent = .spaces(0)
         guard !isStartOfFile else { break }
 
         if requiresNextNewline ||
@@ -3372,9 +3381,17 @@ fileprivate final class TokenStreamCreator: SyntaxVisitor {
         let isBOM = text == "\u{feff}"
         requiresNextNewline = !isBOM
         isStartOfFile = isStartOfFile && isBOM
+        leadingIndent = nil
 
-      default:
-        break
+      case .backslashes, .formfeeds, .pounds, .verticalTabs:
+        leadingIndent = nil
+
+      case .spaces(let n):
+        guard leadingIndent == .spaces(0) else { break }
+        leadingIndent = .spaces(n)
+      case .tabs(let n):
+        guard leadingIndent == .spaces(0) else { break }
+        leadingIndent = .tabs(n)
       }
       position += piece.sourceLength
     }

Tests/SwiftFormatTests/PrettyPrint/CommentTests.swift

@@ -583,14 +583,14 @@ final class CommentTests: PrettyPrintTestCase {
   func testBlockComments() {
     let input =
       """
-      /* Line Comment1 */
+              /* Line Comment1 */
       /* Line Comment2 */
       let a = 123
       let b = "456"  /* End of line comment */
       let c = "More content"
 
-      /* Comment 3
-         Comment 4 */
+            /* Comment 3
+               Comment 4 */
 
       let reallyLongVariableName = 123  /* This comment should wrap */
 
@@ -603,7 +603,9 @@ final class CommentTests: PrettyPrintTestCase {
       }
 
       let d = 123
-      /* Trailing Comment */
+        /* Trailing Comment */
+        /* Trailing
+           Block Comment */
       """
 
     let expected =
@@ -633,6 +635,8 @@ final class CommentTests: PrettyPrintTestCase {
 
       let d = 123
       /* Trailing Comment */
+      /* Trailing
+         Block Comment */
 
       """