dart / pub / 978cc9c4be7d8978348e56d4ae82be8257a59579 / . / lib / src / solver / partial_solution.dart

// Copyright (c) 2017, 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. | |

import '../package_name.dart'; | |

import 'assignment.dart'; | |

import 'incompatibility.dart'; | |

import 'set_relation.dart'; | |

import 'term.dart'; | |

/// A list of [Assignment]s that represent the solver's current best guess about | |

/// what's true for the eventual set of package versions that will comprise the | |

/// total solution. | |

/// | |

/// See https://github.com/dart-lang/pub/tree/master/doc/solver.md#partial-solution. | |

class PartialSolution { | |

/// The assignments that have been made so far, in the order they were | |

/// assigned. | |

final _assignments = <Assignment>[]; | |

/// The decisions made for each package. | |

final _decisions = <String, PackageId>{}; | |

/// The intersection of all positive [Assignment]s for each package, minus any | |

/// negative [Assignment]s that refer to that package. | |

/// | |

/// This is derived from [_assignments]. | |

final _positive = <String, Term>{}; | |

/// The union of all negative [Assignment]s for each package. | |

/// | |

/// If a package has any positive [Assignment]s, it doesn't appear in this | |

/// map. | |

/// | |

/// This is derived from [_assignments]. | |

final _negative = <String, Map<PackageRef, Term>>{}; | |

/// Returns all the decisions that have been made in this partial solution. | |

Iterable<PackageId> get decisions => _decisions.values; | |

/// Returns all [PackageRange]s that have been assigned but are not yet | |

/// satisfied. | |

Iterable<PackageRange> get unsatisfied => _positive.values | |

.where((term) => !_decisions.containsKey(term.package.name)) | |

.map((term) => term.package); | |

// The current decision levelâ€”that is, the length of [decisions]. | |

int get decisionLevel => _decisions.length; | |

/// The number of distinct solutions that have been attempted so far. | |

int get attemptedSolutions => _attemptedSolutions; | |

var _attemptedSolutions = 1; | |

/// Whether the solver is currently backtracking. | |

var _backtracking = false; | |

/// Adds an assignment of [package] as a decision and increments the | |

/// [decisionLevel]. | |

void decide(PackageId package) { | |

// When we make a new decision after backtracking, count an additional | |

// attempted solution. If we backtrack multiple times in a row, though, we | |

// only want to count one, since we haven't actually started attempting a | |

// new solution. | |

if (_backtracking) _attemptedSolutions++; | |

_backtracking = false; | |

_decisions[package.name] = package; | |

_assign(Assignment.decision(package, decisionLevel, _assignments.length)); | |

} | |

/// Adds an assignment of [package] as a derivation. | |

void derive(PackageName package, bool isPositive, Incompatibility cause) { | |

_assign(Assignment.derivation( | |

package, isPositive, cause, decisionLevel, _assignments.length)); | |

} | |

/// Adds [assignment] to [_assignments] and [_positive] or [_negative]. | |

void _assign(Assignment assignment) { | |

_assignments.add(assignment); | |

_register(assignment); | |

} | |

/// Resets the current decision level to [decisionLevel], and removes all | |

/// assignments made after that level. | |

void backtrack(int decisionLevel) { | |

_backtracking = true; | |

var packages = <String>{}; | |

while (_assignments.last.decisionLevel > decisionLevel) { | |

var removed = _assignments.removeLast(); | |

packages.add(removed.package.name); | |

if (removed.isDecision) _decisions.remove(removed.package.name); | |

} | |

// Re-compute [_positive] and [_negative] for the packages that were removed. | |

for (var package in packages) { | |

_positive.remove(package); | |

_negative.remove(package); | |

} | |

for (var assignment in _assignments) { | |

if (packages.contains(assignment.package.name)) { | |

_register(assignment); | |

} | |

} | |

} | |

/// Registers [assignment] in [_positive] or [_negative]. | |

void _register(Assignment assignment) { | |

var name = assignment.package.name; | |

var oldPositive = _positive[name]; | |

if (oldPositive != null) { | |

_positive[name] = oldPositive.intersect(assignment); | |

return; | |

} | |

var ref = assignment.package.toRef(); | |

var negativeByRef = _negative[name]; | |

var oldNegative = negativeByRef == null ? null : negativeByRef[ref]; | |

var term = | |

oldNegative == null ? assignment : assignment.intersect(oldNegative); | |

if (term.isPositive) { | |

_negative.remove(name); | |

_positive[name] = term; | |

} else { | |

_negative.putIfAbsent(name, () => {})[ref] = term; | |

} | |

} | |

/// Returns the first [Assignment] in this solution such that the sublist of | |

/// assignments up to and including that entry collectively satisfies [term]. | |

/// | |

/// Throws a [StateError] if [term] isn't satisfied by [this]. | |

Assignment satisfier(Term term) { | |

Term assignedTerm; | |

for (var assignment in _assignments) { | |

if (assignment.package.name != term.package.name) continue; | |

if (!assignment.package.isRoot && | |

!assignment.package.samePackage(term.package)) { | |

// not foo from hosted has no bearing on foo from git | |

if (!assignment.isPositive) continue; | |

// foo from hosted satisfies not foo from git | |

assert(!term.isPositive); | |

return assignment; | |

} | |

assignedTerm = assignedTerm == null | |

? assignment | |

: assignedTerm.intersect(assignment); | |

// As soon as we have enough assignments to satisfy [term], return them. | |

if (assignedTerm.satisfies(term)) return assignment; | |

} | |

throw StateError('[BUG] $term is not satisfied.'); | |

} | |

/// Returns whether [this] satisfies [other]. | |

/// | |

/// That is, whether [other] must be true given the assignments in this | |

/// partial solution. | |

bool satisfies(Term term) => relation(term) == SetRelation.subset; | |

/// Returns the relationship between the package versions allowed by all | |

/// assignments in [this] and those allowed by [term]. | |

SetRelation relation(Term term) { | |

var positive = _positive[term.package.name]; | |

if (positive != null) return positive.relation(term); | |

// If there are no assignments related to [term], that means the | |

// assignments allow any version of any package, which is a superset of | |

// [term]. | |

var byRef = _negative[term.package.name]; | |

if (byRef == null) return SetRelation.overlapping; | |

// not foo from git is a superset of foo from hosted | |

// not foo from git overlaps not foo from hosted | |

var negative = byRef[term.package.toRef()]; | |

if (negative == null) return SetRelation.overlapping; | |

return negative.relation(term); | |

} | |

} |