Add support for re-indenting block comments.

Re-indent all lines of a block comment with the current indentation
level. The comment must not have anything other than whitespace
preceding it on the line, and all lines must have at least that level
of whitespace (or be empty).

Author: shawnhyam

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 */
 
       """