lib/src/line_splitting/solve_state.dart - dart_style - Git at Google

 // 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.line_splitting.solve_state;

 import '../debug.dart' as debug;
 import '../rule/rule.dart';
 import 'line_splitter.dart';
 import 'rule_set.dart';

 /// A possibly incomplete solution in the line splitting search space.
 ///
 /// A single [SolveState] binds some subset of the rules to values while
 /// leaving the rest unbound. If every rule is bound, the solve state describes
 /// a complete solution to the line splitting problem. Even if rules are
 /// unbound, a state can also usually be used as a solution by treating all
 /// unbound rules as unsplit. (The usually is because a state that constrains
 /// an unbound rule to split can't be used with that rule unsplit.)
 ///
 /// From a given solve state, we can explore the search tree to more refined
 /// solve states by producing new ones that add more bound rules to the current
 /// state.
 class SolveState {
   final LineSplitter _splitter;
   final RuleSet _ruleValues;

   /// The unbound rules in this state that can be bound to produce new more
   /// refined states.
   ///
   /// Keeping this set small is the key to make the entire line splitter
   /// perform well. If we consider too make rules at each state, our
   /// exploration of the solution space is too branchy and we waste time on
   /// dead end solutions.
   ///
   /// Here is the key insight. The line splitter treats any unbound rule as
   /// being unsplit. This means refining a solution always means taking a rule
   /// that is unsplit and making it split. That monotonically increases the
   /// cost, but may help fit the solution inside the page.
   ///
   /// We want to keep the cost low, so the only reason to consider making a
   /// rule split is if it reduces an overflowing line. It's also the case that
   /// splitting an earlier rule will often reshuffle the rest of the line.
   ///
   /// Taking that into account, the only rules we consider binding to extend a
   /// solve state are *unbound rules inside the first line that is overflowing*.
   /// Even if a line has dozens of rules, this generally keeps the branching
   /// down to a few. It also means rules inside lines that already fit are
   /// never touched.
   ///
   /// There is one other set of rules that go in here. Sometimes a bound rule
   /// in the solve state constrains some other unbound rule to split. In that
   /// case, we also consider that active so we know to not leave it at zero.
   final _liveRules = new Set<Rule>();

   /// The set of splits chosen for this state.
   SplitSet get splits => _splits;
   SplitSet _splits;

   /// The number of characters that do not fit inside the page with this set of
   /// splits.
   int get overflowChars => _overflowChars;
   int _overflowChars;

   /// Whether we can treat this state as a complete solution by leaving its
   /// unbound rules unsplit.
   ///
   /// This is generally true but will be false if the state contains any
   /// unbound rules that are constrained to not be zero by other bound rules.
   /// This avoids picking a solution that leaves those rules at zero when they
   /// aren't allowed to be.
   bool _isComplete = true;

   /// The constraints the bound rules in this state have on the remaining
   /// unbound rules.
   Map<Rule, int> _constraints;

   /// The bound rules that appear inside lines also containing unbound rules.
   ///
   /// By appearing in the same line, it means these bound rules may affect the
   /// results of binding those unbound rules. This is used to tell if two
   /// states may diverge by binding unbound rules or not.
   Set<Rule> _boundRulesInUnboundLines;

   SolveState(this._splitter, this._ruleValues) {
     _calculateSplits();
     _calculateCost();
   }

   /// Gets the value to use for [rule], either the bound value or `0` if it
   /// isn't bound.
   int getValue(Rule rule) {
     if (rule is HardSplitRule) return 0;

     return _ruleValues.getValue(rule);
   }

   /// Returns `true` if this state is a better solution to use as the final
   /// result than [other].
   bool isBetterThan(SolveState other) {
     // If this state contains an unbound rule that we know can't be left
     // unsplit, we can't pick this as a solution.
     if (!_isComplete) return false;

     // Anything is better than nothing.
     if (other == null) return true;

     // Prefer the solution that fits the most in the page.
     if (overflowChars != other.overflowChars) {
       return overflowChars < other.overflowChars;
     }

     // Otherwise, prefer the best cost.
     return splits.cost < other.splits.cost;
   }

   /// Determines if this state "overlaps" [other].
   ///
   /// Two states overlap if they currently have the same score and we can tell
   /// for certain that they won't diverge as their unbound rules are bound. If
   /// that's the case, then whichever state is better now (based on their
   /// currently bound rule values) is the one that will always win, regardless
   /// of how they get expanded.
   ///
   /// In other words, their entire expanded solution trees also overlap. In
   /// that case, there's no point in expanding both, so we can just pick the
   /// winner now and discard the other.
   ///
   /// For this to be true, we need to prove that binding an unbound rule won't
   /// affect one state differently from the other. We have to show that they
   /// are parallel.
   ///
   /// Two things could cause this *not* to be the case.
   ///
   /// 1. If one state's bound rules place different constraints on the unbound
   ///    rules than the other.
   ///
   /// 2. If one state's different bound rules are in the same line as an
   ///    unbound rule. That affects the indentation and length of the line,
   ///    which affects the context where the unbound rule is being chosen.
   ///
   /// If neither of these is the case, the states overlap. Returns `<0` if this
   /// state is better, or `>0` if [other] wins. If the states do not overlap,
   /// returns `0`.
   int compareOverlap(SolveState other) {
     if (!_isOverlapping(other)) return 0;

     // They do overlap, so see which one wins.
     for (var rule in _splitter.rules) {
       var value = _ruleValues.getValue(rule);
       var otherValue = other._ruleValues.getValue(rule);

       if (value != otherValue) return value.compareTo(otherValue);
     }

     // The way SolveStates are expanded should guarantee that we never generate
     // the exact same state twice. Getting here implies that that failed.
     throw "unreachable";
   }

   /// Enqueues more solve states to consider based on this one.
   ///
   /// For each unbound rule in this state that occurred in the first long line,
   /// enqueue solve states that bind that rule to each value it can have and
   /// bind all previous rules to zero. (In other words, try all subsolutions
   /// where that rule becomes the first new rule to split at.)
   void expand() {
     var unsplitRules = _ruleValues.clone();

     // Walk down the rules looking for unbound ones to try.
     var triedRules = 0;
     for (var rule in _splitter.rules) {
       if (_liveRules.contains(rule)) {
         // We found one worth trying, so try all of its values.
         for (var value = 1; value < rule.numValues; value++) {
           var boundRules = unsplitRules.clone();

           var mustSplitRules;
           var valid = boundRules.tryBind(_splitter.rules, rule, value, (rule) {
             if (mustSplitRules == null) mustSplitRules = [];
             mustSplitRules.add(rule);
           });

           // Make sure we don't violate the constraints of the bound rules.
           if (!valid) continue;

           var state = new SolveState(_splitter, boundRules);

           // If some unbound rules are constrained to split, remember that.
           if (mustSplitRules != null) {
             state._isComplete = false;
             state._liveRules.addAll(mustSplitRules);
           }

           _splitter.enqueue(state);
         }

         // Stop once we've tried all of the ones we can.
         if (++triedRules == _liveRules.length) break;
       }

       // Fill in previous unbound rules with zero.
       if (!_ruleValues.contains(rule)) {
         // Pass a dummy callback because zero will never fail. (If it would
         // have, that rule would already be bound to some other value.)
         if (!unsplitRules.tryBind(_splitter.rules, rule, 0, (_) {})) {
           break;
         }
       }
     }
   }

   /// Returns `true` if [other] overlaps this state.
   bool _isOverlapping(SolveState other) {
     _ensureOverlapFields();
     other._ensureOverlapFields();

     // Lines that contain both bound and unbound rules must have the same
     // bound values.
     if (_boundRulesInUnboundLines.length !=
         other._boundRulesInUnboundLines.length) {
       return false;
     }

     for (var rule in _boundRulesInUnboundLines) {
       if (!other._boundRulesInUnboundLines.contains(rule)) return false;
       if (_ruleValues.getValue(rule) != other._ruleValues.getValue(rule)) {
         return false;
       }
     }

     if (_constraints.length != other._constraints.length) return false;

     for (var rule in _constraints.keys) {
       if (_constraints[rule] != other._constraints[rule]) return false;
     }

     return true;
   }

   /// Calculates the [SplitSet] for this solve state, assuming any unbound
   /// rules are set to zero.
   void _calculateSplits() {
     // Figure out which expression nesting levels got split and need to be
     // assigned columns.
     var usedNestingLevels = new Set();
     for (var i = 0; i < _splitter.chunks.length - 1; i++) {
       var chunk = _splitter.chunks[i];
       if (chunk.rule.isSplit(getValue(chunk.rule), chunk)) {
         usedNestingLevels.add(chunk.nesting);
         chunk.nesting.clearTotalUsedIndent();
       }
     }

     for (var nesting in usedNestingLevels) {
       nesting.refreshTotalUsedIndent(usedNestingLevels);
     }

     _splits = new SplitSet(_splitter.chunks.length);
     for (var i = 0; i < _splitter.chunks.length - 1; i++) {
       var chunk = _splitter.chunks[i];
       if (chunk.rule.isSplit(getValue(chunk.rule), chunk)) {
         var indent = 0;
         if (!chunk.flushLeftAfter) {
           // Add in the chunk's indent.
           indent = _splitter.blockIndentation + chunk.indent;

           // And any expression nesting.
           indent += chunk.nesting.totalUsedIndent;
         }

         _splits.add(i, indent);
       }
     }
   }

   /// Evaluates the cost (i.e. the relative "badness") of splitting the line
   /// into [lines] physical lines based on the current set of rules.
   void _calculateCost() {
     assert(_splits != null);

     // Calculate the length of each line and apply the cost of any spans that
     // get split.
     var cost = 0;
     _overflowChars = 0;

     var length = _splitter.firstLineIndent;

     // The unbound rules in use by the current line. This will be null after
     // the first long line has completed.
     var currentLineRules = [];

     endLine(int end) {
       // Track lines that went over the length. It is only rules contained in
       // long lines that we may want to split.
       if (length > _splitter.writer.pageWidth) {
         _overflowChars += length - _splitter.writer.pageWidth;

         // Only try rules that are in the first long line, since we know at
         // least one of them *will* be split.
         if (currentLineRules != null && currentLineRules.isNotEmpty) {
           _liveRules.addAll(currentLineRules);
           currentLineRules = null;
         }
       } else {
         // The line fit, so don't keep track of its rules.
         if (currentLineRules != null) {
           currentLineRules.clear();
         }
       }
     }

     // The set of spans that contain chunks that ended up splitting. We store
     // these in a set so a span's cost doesn't get double-counted if more than
     // one split occurs in it.
     var splitSpans = new Set();

     for (var i = 0; i < _splitter.chunks.length; i++) {
       var chunk = _splitter.chunks[i];

       length += chunk.text.length;

       // Ignore the split after the last chunk.
       if (i == _splitter.chunks.length - 1) break;

       if (_splits.shouldSplitAt(i)) {
         endLine(i);

         splitSpans.addAll(chunk.spans);

         // Include the cost of the nested block.
         if (chunk.blockChunks.isNotEmpty) {
           cost +=
               _splitter.writer.formatBlock(chunk, _splits.getColumn(i)).cost;
         }

         // Start the new line.
         length = _splits.getColumn(i);
       } else {
         if (chunk.spaceWhenUnsplit) length++;

         // Include the nested block inline, if any.
         length += chunk.unsplitBlockLength;

         // If we might be in the first overly long line, keep track of any
         // unbound rules we encounter. These are ones that we'll want to try to
         // bind to shorten the long line.
         if (currentLineRules != null &&
             chunk.rule != null &&
             !chunk.isHardSplit &&
             !_ruleValues.contains(chunk.rule)) {
           currentLineRules.add(chunk.rule);
         }
       }
     }

     // Add the costs for the rules that split.
     _ruleValues.forEach(_splitter.rules, (rule, value) {
       // A rule may be bound to zero if another rule constrains it to not split.
       if (value != 0) cost += rule.cost;
     });

     // Add the costs for the spans containing splits.
     for (var span in splitSpans) cost += span.cost;

     // Finish the last line.
     endLine(_splitter.chunks.length);

     _splits.setCost(cost);
   }

   /// Lazily initializes the fields needed to compare two states for overlap.
   ///
   /// We do this lazily because the calculation is a bit slow, and is only
   /// needed when we have two states with the same score.
   void _ensureOverlapFields() {
     if (_constraints != null) return;

     _calculateConstraints();
     _calculateBoundRulesInUnboundLines();
   }

   /// Initializes [_constraints] with any constraints the bound rules place on
   /// the unbound rules.
   void _calculateConstraints() {
     _constraints = {};

     var unboundRules = [];
     var boundRules = [];

     for (var rule in _splitter.rules) {
       if (_ruleValues.contains(rule)) {
         boundRules.add(rule);
       } else {
         unboundRules.add(rule);
       }
     }

     for (var bound in boundRules) {
       var value = _ruleValues.getValue(bound);

       for (var unbound in unboundRules) {
         var constraint = bound.constrain(value, unbound);
         if (constraint != null) {
           _constraints[unbound] = constraint;
         }
       }
     }
   }

   void _calculateBoundRulesInUnboundLines() {
     _boundRulesInUnboundLines = new Set();

     var boundInLine = new Set();
     var hasUnbound = false;

     for (var i = 0; i < _splitter.chunks.length - 1; i++) {
       if (splits.shouldSplitAt(i)) {
         if (hasUnbound) _boundRulesInUnboundLines.addAll(boundInLine);

         boundInLine.clear();
         hasUnbound = false;
       }

       var rule = _splitter.chunks[i].rule;
       if (rule != null && rule is! HardSplitRule) {
         if (_ruleValues.contains(rule)) {
           boundInLine.add(rule);
         } else {
           hasUnbound = true;
         }
       }
     }

     if (hasUnbound) _boundRulesInUnboundLines.addAll(boundInLine);
   }

   String toString() {
     var buffer = new StringBuffer();

     buffer.writeAll(_splitter.rules.map((rule) {
       var valueLength = "${rule.fullySplitValue}".length;

       var value = "?";
       if (_ruleValues.contains(rule)) {
         value = "${_ruleValues.getValue(rule)}";
       }

       value = value.padLeft(valueLength);
       if (_liveRules.contains(rule)) {
         value = debug.bold(value);
       } else {
         value = debug.gray(value);
       }

       return value;
     }), " ");

     buffer.write("   \$${splits.cost}");

     if (overflowChars > 0) buffer.write(" (${overflowChars} over)");
     if (!_isComplete) buffer.write(" (incomplete)");
     if (splits == null) buffer.write(" invalid");

     return buffer.toString();
   }
 }
	// 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.line_splitting.solve_state;

	import '../debug.dart' as debug;
	import '../rule/rule.dart';
	import 'line_splitter.dart';
	import 'rule_set.dart';

	/// A possibly incomplete solution in the line splitting search space.
	///
	/// A single [SolveState] binds some subset of the rules to values while
	/// leaving the rest unbound. If every rule is bound, the solve state describes
	/// a complete solution to the line splitting problem. Even if rules are
	/// unbound, a state can also usually be used as a solution by treating all
	/// unbound rules as unsplit. (The usually is because a state that constrains
	/// an unbound rule to split can't be used with that rule unsplit.)
	///
	/// From a given solve state, we can explore the search tree to more refined
	/// solve states by producing new ones that add more bound rules to the current
	/// state.
	class SolveState {
	final LineSplitter _splitter;
	final RuleSet _ruleValues;

	/// The unbound rules in this state that can be bound to produce new more
	/// refined states.
	///
	/// Keeping this set small is the key to make the entire line splitter
	/// perform well. If we consider too make rules at each state, our
	/// exploration of the solution space is too branchy and we waste time on
	/// dead end solutions.
	///
	/// Here is the key insight. The line splitter treats any unbound rule as
	/// being unsplit. This means refining a solution always means taking a rule
	/// that is unsplit and making it split. That monotonically increases the
	/// cost, but may help fit the solution inside the page.
	///
	/// We want to keep the cost low, so the only reason to consider making a
	/// rule split is if it reduces an overflowing line. It's also the case that
	/// splitting an earlier rule will often reshuffle the rest of the line.
	///
	/// Taking that into account, the only rules we consider binding to extend a
	/// solve state are unbound rules inside the first line that is overflowing.
	/// Even if a line has dozens of rules, this generally keeps the branching
	/// down to a few. It also means rules inside lines that already fit are
	/// never touched.
	///
	/// There is one other set of rules that go in here. Sometimes a bound rule
	/// in the solve state constrains some other unbound rule to split. In that
	/// case, we also consider that active so we know to not leave it at zero.
	final _liveRules = new Set<Rule>();

	/// The set of splits chosen for this state.
	SplitSet get splits => _splits;
	SplitSet _splits;

	/// The number of characters that do not fit inside the page with this set of
	/// splits.
	int get overflowChars => _overflowChars;
	int _overflowChars;

	/// Whether we can treat this state as a complete solution by leaving its
	/// unbound rules unsplit.
	///
	/// This is generally true but will be false if the state contains any
	/// unbound rules that are constrained to not be zero by other bound rules.
	/// This avoids picking a solution that leaves those rules at zero when they
	/// aren't allowed to be.
	bool _isComplete = true;

	/// The constraints the bound rules in this state have on the remaining
	/// unbound rules.
	Map<Rule, int> _constraints;

	/// The bound rules that appear inside lines also containing unbound rules.
	///
	/// By appearing in the same line, it means these bound rules may affect the
	/// results of binding those unbound rules. This is used to tell if two
	/// states may diverge by binding unbound rules or not.
	Set<Rule> _boundRulesInUnboundLines;

	SolveState(this._splitter, this._ruleValues) {
	_calculateSplits();
	_calculateCost();
	}

	/// Gets the value to use for [rule], either the bound value or `0` if it
	/// isn't bound.
	int getValue(Rule rule) {
	if (rule is HardSplitRule) return 0;

	return _ruleValues.getValue(rule);
	}

	/// Returns `true` if this state is a better solution to use as the final
	/// result than [other].
	bool isBetterThan(SolveState other) {
	// If this state contains an unbound rule that we know can't be left
	// unsplit, we can't pick this as a solution.
	if (!_isComplete) return false;

	// Anything is better than nothing.
	if (other == null) return true;

	// Prefer the solution that fits the most in the page.
	if (overflowChars != other.overflowChars) {
	return overflowChars < other.overflowChars;
	}

	// Otherwise, prefer the best cost.
	return splits.cost < other.splits.cost;
	}

	/// Determines if this state "overlaps" [other].
	///
	/// Two states overlap if they currently have the same score and we can tell
	/// for certain that they won't diverge as their unbound rules are bound. If
	/// that's the case, then whichever state is better now (based on their
	/// currently bound rule values) is the one that will always win, regardless
	/// of how they get expanded.
	///
	/// In other words, their entire expanded solution trees also overlap. In
	/// that case, there's no point in expanding both, so we can just pick the
	/// winner now and discard the other.
	///
	/// For this to be true, we need to prove that binding an unbound rule won't
	/// affect one state differently from the other. We have to show that they
	/// are parallel.
	///
	/// Two things could cause this not to be the case.
	///
	/// 1. If one state's bound rules place different constraints on the unbound
	/// rules than the other.
	///
	/// 2. If one state's different bound rules are in the same line as an
	/// unbound rule. That affects the indentation and length of the line,
	/// which affects the context where the unbound rule is being chosen.
	///
	/// If neither of these is the case, the states overlap. Returns `<0` if this
	/// state is better, or `>0` if [other] wins. If the states do not overlap,
	/// returns `0`.
	int compareOverlap(SolveState other) {
	if (!_isOverlapping(other)) return 0;

	// They do overlap, so see which one wins.
	for (var rule in _splitter.rules) {
	var value = _ruleValues.getValue(rule);
	var otherValue = other._ruleValues.getValue(rule);

	if (value != otherValue) return value.compareTo(otherValue);
	}

	// The way SolveStates are expanded should guarantee that we never generate
	// the exact same state twice. Getting here implies that that failed.
	throw "unreachable";
	}

	/// Enqueues more solve states to consider based on this one.
	///
	/// For each unbound rule in this state that occurred in the first long line,
	/// enqueue solve states that bind that rule to each value it can have and
	/// bind all previous rules to zero. (In other words, try all subsolutions
	/// where that rule becomes the first new rule to split at.)
	void expand() {
	var unsplitRules = _ruleValues.clone();

	// Walk down the rules looking for unbound ones to try.
	var triedRules = 0;
	for (var rule in _splitter.rules) {
	if (_liveRules.contains(rule)) {
	// We found one worth trying, so try all of its values.
	for (var value = 1; value < rule.numValues; value++) {
	var boundRules = unsplitRules.clone();

	var mustSplitRules;
	var valid = boundRules.tryBind(_splitter.rules, rule, value, (rule) {
	if (mustSplitRules == null) mustSplitRules = [];
	mustSplitRules.add(rule);
	});

	// Make sure we don't violate the constraints of the bound rules.
	if (!valid) continue;

	var state = new SolveState(_splitter, boundRules);

	// If some unbound rules are constrained to split, remember that.
	if (mustSplitRules != null) {
	state._isComplete = false;
	state._liveRules.addAll(mustSplitRules);
	}

	_splitter.enqueue(state);
	}

	// Stop once we've tried all of the ones we can.
	if (++triedRules == _liveRules.length) break;
	}

	// Fill in previous unbound rules with zero.
	if (!_ruleValues.contains(rule)) {
	// Pass a dummy callback because zero will never fail. (If it would
	// have, that rule would already be bound to some other value.)
	if (!unsplitRules.tryBind(_splitter.rules, rule, 0, (_) {})) {
	break;
	}
	}
	}
	}

	/// Returns `true` if [other] overlaps this state.
	bool _isOverlapping(SolveState other) {
	_ensureOverlapFields();
	other._ensureOverlapFields();

	// Lines that contain both bound and unbound rules must have the same
	// bound values.
	if (_boundRulesInUnboundLines.length !=
	other._boundRulesInUnboundLines.length) {
	return false;
	}

	for (var rule in _boundRulesInUnboundLines) {
	if (!other._boundRulesInUnboundLines.contains(rule)) return false;
	if (_ruleValues.getValue(rule) != other._ruleValues.getValue(rule)) {
	return false;
	}
	}

	if (_constraints.length != other._constraints.length) return false;

	for (var rule in _constraints.keys) {
	if (_constraints[rule] != other._constraints[rule]) return false;
	}

	return true;
	}

	/// Calculates the [SplitSet] for this solve state, assuming any unbound
	/// rules are set to zero.
	void _calculateSplits() {
	// Figure out which expression nesting levels got split and need to be
	// assigned columns.
	var usedNestingLevels = new Set();
	for (var i = 0; i < _splitter.chunks.length - 1; i++) {
	var chunk = _splitter.chunks[i];
	if (chunk.rule.isSplit(getValue(chunk.rule), chunk)) {
	usedNestingLevels.add(chunk.nesting);
	chunk.nesting.clearTotalUsedIndent();
	}
	}

	for (var nesting in usedNestingLevels) {
	nesting.refreshTotalUsedIndent(usedNestingLevels);
	}

	_splits = new SplitSet(_splitter.chunks.length);
	for (var i = 0; i < _splitter.chunks.length - 1; i++) {
	var chunk = _splitter.chunks[i];
	if (chunk.rule.isSplit(getValue(chunk.rule), chunk)) {
	var indent = 0;
	if (!chunk.flushLeftAfter) {
	// Add in the chunk's indent.
	indent = _splitter.blockIndentation + chunk.indent;

	// And any expression nesting.
	indent += chunk.nesting.totalUsedIndent;
	}

	_splits.add(i, indent);
	}
	}
	}

	/// Evaluates the cost (i.e. the relative "badness") of splitting the line
	/// into [lines] physical lines based on the current set of rules.
	void _calculateCost() {
	assert(_splits != null);

	// Calculate the length of each line and apply the cost of any spans that
	// get split.
	var cost = 0;
	_overflowChars = 0;

	var length = _splitter.firstLineIndent;

	// The unbound rules in use by the current line. This will be null after
	// the first long line has completed.
	var currentLineRules = [];

	endLine(int end) {
	// Track lines that went over the length. It is only rules contained in
	// long lines that we may want to split.
	if (length > _splitter.writer.pageWidth) {
	_overflowChars += length - _splitter.writer.pageWidth;

	// Only try rules that are in the first long line, since we know at
	// least one of them will be split.
	if (currentLineRules != null && currentLineRules.isNotEmpty) {
	_liveRules.addAll(currentLineRules);
	currentLineRules = null;
	}
	} else {
	// The line fit, so don't keep track of its rules.
	if (currentLineRules != null) {
	currentLineRules.clear();
	}
	}
	}

	// The set of spans that contain chunks that ended up splitting. We store
	// these in a set so a span's cost doesn't get double-counted if more than
	// one split occurs in it.
	var splitSpans = new Set();

	for (var i = 0; i < _splitter.chunks.length; i++) {
	var chunk = _splitter.chunks[i];

	length += chunk.text.length;

	// Ignore the split after the last chunk.
	if (i == _splitter.chunks.length - 1) break;

	if (_splits.shouldSplitAt(i)) {
	endLine(i);

	splitSpans.addAll(chunk.spans);

	// Include the cost of the nested block.
	if (chunk.blockChunks.isNotEmpty) {
	cost +=
	_splitter.writer.formatBlock(chunk, _splits.getColumn(i)).cost;
	}

	// Start the new line.
	length = _splits.getColumn(i);
	} else {
	if (chunk.spaceWhenUnsplit) length++;

	// Include the nested block inline, if any.
	length += chunk.unsplitBlockLength;

	// If we might be in the first overly long line, keep track of any
	// unbound rules we encounter. These are ones that we'll want to try to
	// bind to shorten the long line.
	if (currentLineRules != null &&
	chunk.rule != null &&
	!chunk.isHardSplit &&
	!_ruleValues.contains(chunk.rule)) {
	currentLineRules.add(chunk.rule);
	}
	}
	}

	// Add the costs for the rules that split.
	_ruleValues.forEach(_splitter.rules, (rule, value) {
	// A rule may be bound to zero if another rule constrains it to not split.
	if (value != 0) cost += rule.cost;
	});

	// Add the costs for the spans containing splits.
	for (var span in splitSpans) cost += span.cost;

	// Finish the last line.
	endLine(_splitter.chunks.length);

	_splits.setCost(cost);
	}

	/// Lazily initializes the fields needed to compare two states for overlap.
	///
	/// We do this lazily because the calculation is a bit slow, and is only
	/// needed when we have two states with the same score.
	void _ensureOverlapFields() {
	if (_constraints != null) return;

	_calculateConstraints();
	_calculateBoundRulesInUnboundLines();
	}

	/// Initializes [_constraints] with any constraints the bound rules place on
	/// the unbound rules.
	void _calculateConstraints() {
	_constraints = {};

	var unboundRules = [];
	var boundRules = [];

	for (var rule in _splitter.rules) {
	if (_ruleValues.contains(rule)) {
	boundRules.add(rule);
	} else {
	unboundRules.add(rule);
	}
	}

	for (var bound in boundRules) {
	var value = _ruleValues.getValue(bound);

	for (var unbound in unboundRules) {
	var constraint = bound.constrain(value, unbound);
	if (constraint != null) {
	_constraints[unbound] = constraint;
	}
	}
	}
	}

	void _calculateBoundRulesInUnboundLines() {
	_boundRulesInUnboundLines = new Set();

	var boundInLine = new Set();
	var hasUnbound = false;

	for (var i = 0; i < _splitter.chunks.length - 1; i++) {
	if (splits.shouldSplitAt(i)) {
	if (hasUnbound) _boundRulesInUnboundLines.addAll(boundInLine);

	boundInLine.clear();
	hasUnbound = false;
	}

	var rule = _splitter.chunks[i].rule;
	if (rule != null && rule is! HardSplitRule) {
	if (_ruleValues.contains(rule)) {
	boundInLine.add(rule);
	} else {
	hasUnbound = true;
	}
	}
	}

	if (hasUnbound) _boundRulesInUnboundLines.addAll(boundInLine);
	}

	String toString() {
	var buffer = new StringBuffer();

	buffer.writeAll(_splitter.rules.map((rule) {
	var valueLength = "${rule.fullySplitValue}".length;

	var value = "?";
	if (_ruleValues.contains(rule)) {
	value = "${_ruleValues.getValue(rule)}";
	}

	value = value.padLeft(valueLength);
	if (_liveRules.contains(rule)) {
	value = debug.bold(value);
	} else {
	value = debug.gray(value);
	}

	return value;
	}), " ");

	buffer.write(" \$${splits.cost}");

	if (overflowChars > 0) buffer.write(" (${overflowChars} over)");
	if (!_isComplete) buffer.write(" (incomplete)");
	if (splits == null) buffer.write(" invalid");

	return buffer.toString();
	}
	}