Fix bug with comments being reordered.

In certain locations, if you had multiple inline block comments on the same line, they would get reordered. That in turn would (correctly) trip the formatter's internal "whitespace-only changes" sanity check and lead to it aborting.

Fix #1667.

Author: munificent

lib/src/front_end/piece_writer.dart

@@ -398,6 +398,7 @@ final class PieceWriter {
     if (comments.isEmpty) return const [];
 
     var leadingComments = <Piece>[];
+    var afterHanging = false;
     for (var i = 0; i < comments.length; i++) {
       var comment = comments[i];
 
@@ -411,12 +412,16 @@ final class PieceWriter {
 
       var piece = commentPiece(comment, trailingWhitespace);
 
-      if (comments.isHanging(i)) {
+      if (!afterHanging && comments.isHanging(i)) {
         // Attach it to the previous CodePiece.
         _previousCode!.addHangingComment(piece);
       } else {
         // Add it to the list of leading comments for the upcoming token.
         leadingComments.add(piece);
+
+        // Once we've found a single non-hanging comment, all subsequent ones
+        // must also be non-hanging since they follow it.
+        afterHanging = true;
       }
     }
 

test/tall/regression/1600/1667.unit

@@ -0,0 +1,47 @@
+>>>
+/*Debugger:stepOver*/
+void main() {
+  /*bl*/ /*sl:1*/ var data = [1, 2, 3];
+  for (
+      // comment forcing formatting
+      /*sl:3*/ /*sl:5*/ /*sl:7*/ /*sl:8*/ var datapoint
+      // comment forcing formatting
+      in
+      // comment forcing formatting
+      /*sl:2*/ data
+      // comment forcing formatting
+      ) {
+    /*sl:4*/ /*sl:6*/ /*sl:8*/ print(datapoint);
+  }
+  /*sl:9 */ print('Done');
+}
+<<<
+/*Debugger:stepOver*/
+void main() {
+  /*bl*/ /*sl:1*/
+  var data = [1, 2, 3];
+  for (
+  // comment forcing formatting
+  /*sl:3*/ /*sl:5*/ /*sl:7*/ /*sl:8*/ var datapoint
+      // comment forcing formatting
+      in
+      // comment forcing formatting
+      /*sl:2*/ data
+  // comment forcing formatting
+  ) {
+    /*sl:4*/ /*sl:6*/ /*sl:8*/
+    print(datapoint);
+  }
+  /*sl:9 */
+  print('Done');
+}
+>>> Minimal repro.
+main() {
+  for (
+      /* 1 */ /* 2 */ datapoint in data) {}
+}
+<<<
+main() {
+  for (
+  /* 1 */ /* 2 */ datapoint in data) {}
+}