New, simpler and faster line splitter.

lib/src/nesting_level.dart

+// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+library dart_style.src.nesting_level;
+
+import 'fast_hash.dart';
+
+/// A single level of expression nesting.
+///
+/// When a line is split in the middle of an expression, this tracks the
+/// context of where in the expression that split occurs. It ensures that the
+/// [LineSplitter] obeys the expression nesting when deciding what column to
+/// start lines at when split inside an expression.
+///
+/// Each instance of this represents a single level of expression nesting. If we
+/// split at to chunks with different levels of nesting, the splitter ensures
+/// they each get assigned to different columns.
+///
+/// In addition, each level has an indent. This is the number of spaces it is
+/// indented relative to the outer expression. It's almost always
+/// [Indent.expression], but cascades are special magic snowflakes and use
+/// [Indent.cascade].
+class NestingLevel extends FastHash {
+  /// The nesting level surrounding this one, or `null` if this is represents
+  /// top level code in a block.
+  NestingLevel get parent => _parent;
+  NestingLevel _parent;
+
+  /// The number of characters that this nesting level is indented relative to
+  /// the containing level.
+  ///
+  /// Normally, this is [Indent.expression], but cascades use [Indent.cascade].
+  final int indent;
+
+  /// The total number of characters of indentation from this level and all of
+  /// its parents, after determining which nesting levels are actually used.
+  ///
+  /// This is only valid during line splitting.
+  int get totalUsedIndent => _totalUsedIndent;
+  int _totalUsedIndent;
+
+  bool get isNested => _parent != null;
+
+  NestingLevel() : indent = 0;
+
+  NestingLevel._(this._parent, this.indent);
+
+  /// Creates a new deeper level of nesting indented [spaces] more characters
+  /// that the outer level.
+  NestingLevel nest(int spaces) => new NestingLevel._(this, spaces);
+
+  /// Clears the previously calculated total indent of this nesting level.
+  void clearTotalUsedIndent() {
+    _totalUsedIndent = null;
+    if (_parent != null) _parent.clearTotalUsedIndent();
+  }
+
+  /// Calculates the total amount of indentation from this nesting level and
+  /// all of its parents assuming only [usedNesting] levels are in use.
+  void refreshTotalUsedIndent(Set<NestingLevel> usedNesting) {
+    if (_totalUsedIndent != null) return;
+
+    _totalUsedIndent = 0;
+
+    if (_parent != null) {
+      _parent.refreshTotalUsedIndent(usedNesting);
+      _totalUsedIndent += _parent.totalUsedIndent;
+    }
+
+    if (usedNesting.contains(this)) _totalUsedIndent += indent;
+  }
+
+  String toString() {
+    if (_parent == null) return indent.toString();
+    return "$parent:$indent";
+  }
+}