Remove _blockCandidates and store block element type on ListElement.

lib/src/front_end/delimited_list_builder.dart

@@ -36,11 +36,6 @@ class DelimitedListBuilder {
 
   final ListStyle _style;
 
-  /// The nodes that have been visited by this builder.
-  ///
-  /// Used to find the block element from them, if desired.
-  final List<AstNode> _blockCandidates = [];
-
   /// The list of comments following the most recently written element before
   /// any comma following the element.
   CommentSequence _commentsBeforeComma = CommentSequence.empty;
@@ -131,8 +126,8 @@ class DelimitedListBuilder {
   /// [addCommentsBefore()] for the first token in the [piece].
   ///
   /// Assumes there is no comma after this piece.
-  void add(Piece piece) {
-    _elements.add(ListElement(piece));
+  void add(Piece piece, [BlockFormat format = BlockFormat.none]) {
+    _elements.add(ListElement(piece, format));
     _commentsBeforeComma = CommentSequence.empty;
   }
 
@@ -148,17 +143,21 @@ class DelimitedListBuilder {
     // Handle comments between the preceding element and this one.
     addCommentsBefore(element.firstNonCommentToken);
 
+    // See if it's an expression that supports block formatting.
+    var format = switch (element) {
+      FunctionExpression() when element.canBlockSplit => BlockFormat.function,
+      Expression() when element.canBlockSplit => BlockFormat.block,
+      _ => BlockFormat.none,
+    };
+
     // Traverse the element itself.
     _visitor.visit(element);
-    add(_visitor.pieces.split());
+    add(_visitor.pieces.split(), format);
 
     var nextToken = element.endToken.next!;
     if (nextToken.lexeme == ',') {
       _commentsBeforeComma = _visitor.takeCommentsBefore(nextToken);
     }
-
-    // If this element might be block formatted, remember it.
-    if (_style.allowBlockElement) _blockCandidates.add(element);
   }
 
   /// Inserts an inner left delimiter between two elements.
@@ -396,14 +395,14 @@ class DelimitedListBuilder {
     var functions = <int>[];
     var others = <int>[];
 
-    for (var i = 0; i < _blockCandidates.length; i++) {
-      var node = _blockCandidates[i];
-      if (node is Expression && node.canBlockSplit) {
-        if (node is FunctionExpression) {
+    for (var i = 0; i < _elements.length; i++) {
+      switch (_elements[i].blockFormat) {
+        case BlockFormat.function:
           functions.add(i);
-        } else {
+        case BlockFormat.block:
           others.add(i);
-        }
+        case BlockFormat.none:
+          break; // Not a block element.
       }
     }
 

lib/src/piece/list.dart

@@ -187,6 +187,9 @@ class ListPiece extends Piece {
 final class ListElement {
   final Piece? _element;
 
+  /// What kind of block formatting can be applied to this element.
+  final BlockFormat blockFormat;
+
   /// If this piece has an opening delimiter after the comma, this is its
   /// lexeme, otherwise an empty string.
   ///
@@ -203,11 +206,14 @@ final class ListElement {
 
   final Piece? _comment;
 
-  ListElement(Piece element, [Piece? comment]) : this._(element, '', comment);
+  ListElement(Piece element, BlockFormat format, [Piece? comment])
+      : this._(element, format, '', comment);
 
-  ListElement.comment(Piece comment) : this._(null, '', comment);
+  ListElement.comment(Piece comment)
+      : this._(null, BlockFormat.none, '', comment);
 
-  ListElement._(this._element, this._delimiter, [this._comment]);
+  ListElement._(this._element, this.blockFormat, this._delimiter,
+      [this._comment]);
 
   /// Writes this element to [writer].
   ///
@@ -239,11 +245,11 @@ final class ListElement {
   /// Returns a new [ListElement] containing this one's element and [comment].
   ListElement withComment(Piece comment) {
     assert(_comment == null); // Shouldn't already have one.
-    return ListElement._(_element, _delimiter, comment);
+    return ListElement._(_element, blockFormat, _delimiter, comment);
   }
 
   ListElement withDelimiter(String delimiter) {
-    return ListElement._(_element, delimiter, _comment);
+    return ListElement._(_element, blockFormat, delimiter, _comment);
   }
 }
 
@@ -264,6 +270,20 @@ enum Commas {
   none,
 }
 
+/// What kind of block formatting style can be applied to the element.
+enum BlockFormat {
+  /// The element is a function expression, which takes priority over other
+  /// kinds of block formatted elements.
+  function,
+
+  /// The element is a collection literal or some other kind expression that
+  /// can be block formatted.
+  block,
+
+  /// The element can't be block formatted.
+  none,
+}
+
 /// The various ways a "list" can appear syntactically and be formatted.
 ///
 /// [ListPiece] is used for most places in code where a series of elements can