Linter Demo

Errors: 10

Warnings: 17

File: /home/fstrocco/Dart/dart/benchmark/dartstyle/lib/src/line_splitting/solve_state.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.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 many 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 unbound rule values that are disallowed because they would place /// invalid constraints on the currently bound values. /// /// For example, say rule A is bound to 1 and B is unbound. If B has value /// 1, it constrains A to be 1. Likewise, if B is 2, it constrains A to be /// 2 as well. Since we already know A is 1, that means we know B cannot be /// bound to value 2. This means B is more limited in this state than it /// might be in another state that binds A to a different value. /// /// It's important to track this, because we can't allow to states to overlap /// if one permits more values for some unbound rule than the other does. Map<Rule, List<int>> _unboundConstraints; /// 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) { // Lines that contain both bound and unbound rules must have the same // bound values. _ensureBoundRulesInUnboundLines(); other._ensureBoundRulesInUnboundLines(); 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; } } _ensureConstraints(); other._ensureConstraints(); if (_constraints.length != other._constraints.length) return false; for (var rule in _constraints.keys) { if (_constraints[rule] != other._constraints[rule]) return false; } if (_unboundConstraints.length != other._unboundConstraints.length) { return false; } for (var rule in _unboundConstraints.keys) { var disallowed = _unboundConstraints[rule]; var otherDisallowed = other._unboundConstraints[rule]; if (disallowed.length != otherDisallowed.length) return false; for (var value in disallowed) { if (!otherDisallowed.contains(value)) 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 foundOverflowRules = false; var start = 0; 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 (!foundOverflowRules) { for (var i = start; i < end; i++) { if (_addLiveRules(_splitter.chunks[i].rule)) { foundOverflowRules = true; } } } } start = end; } // 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(); // The nesting level of the chunk that ended the previous line. var previousNesting; 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; } // Do not allow sequential lines to have the same indentation but for // different reasons. In other words, don't allow different expressions // to claim the same nesting level on subsequent lines. // // A contrived example would be: // // function(inner( // argument), second( // another); // // For the most part, we prevent this by the constraints on splits. // For example, the above can't happen because the split before // "argument", forces the split before "second". // // But there are a couple of squirrely cases where it's hard to prevent // by construction. Instead, this outlaws it by penalizing it very // heavily if it happens to get this far. if (previousNesting != null && chunk.nesting.totalUsedIndent != 0 && chunk.nesting.totalUsedIndent == previousNesting.totalUsedIndent && !identical(chunk.nesting, previousNesting)) { _overflowChars += 10000; } previousNesting = chunk.nesting; // Start the new line. length = _splits.getColumn(i); } else { if (chunk.spaceWhenUnsplit) length++; // Include the nested block inline, if any. length += chunk.unsplitBlockLength; } } // 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); } /// Adds [rule] and all of the rules it constrains to the set of [_liveRules]. /// /// Only does this if [rule] is a valid soft rule. Returns `true` if any new /// live rules were added. bool _addLiveRules(Rule rule) { if (rule == null) return false; if (rule is HardSplitRule) return false; var added = false; for (var constrained in rule.allConstrainedRules) { // The rule may constrain some other rule that was already hardened and // discarded. In that case, we can ignore it. if (constrained.index == null) continue; if (_ruleValues.contains(constrained)) continue; _liveRules.add(constrained); added = true; } return added; } /// Lazily initializes the [_boundInUnboundLines], which is 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 _ensureBoundRulesInUnboundLines() { if (_boundRulesInUnboundLines != null) return; _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); } /// Lazily initializes the [_constraints], which is 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 _ensureConstraints() { if (_constraints != null) return; var unboundRules = []; var boundRules = []; for (var rule in _splitter.rules) { if (_ruleValues.contains(rule)) { boundRules.add(rule); } else { unboundRules.add(rule); } } _constraints = {}; for (var unbound in unboundRules) { for (var bound in boundRules) { var value = _ruleValues.getValue(bound); var constraint = bound.constrain(value, unbound); if (constraint != null) { _constraints[unbound] = constraint; } } } _unboundConstraints = {}; for (var unbound in unboundRules) { var disallowedValues; for (var value = 0; value < unbound.numValues; value++) { for (var j = 0; j < boundRules.length; j++) { var bound = boundRules[j]; var constraint = unbound.constrain(value, bound); // If the unbound rule doesn't place any constraint on this bound // rule, we're fine. if (constraint == null) continue; // If the bound rule's value already meets the constraint it applies, // we don't need to track it. This way, two states that have the // same bound value, one of which has a satisfied constraint, are // still allowed to overlap. var boundValue = _ruleValues.getValue(bound); if (constraint == boundValue) continue; if (constraint == -1 && boundValue != 0) continue; if (disallowedValues == null) { disallowedValues = new Set(); _unboundConstraints[unbound] = disallowedValues; } disallowedValues.add(value); } } } } 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(); } }