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Resolver.swift
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Resolver.swift
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//
// Resolver.swift
// Carthage
//
// Created by Justin Spahr-Summers on 2014-11-09.
// Copyright (c) 2014 Carthage. All rights reserved.
//
import Foundation
import Result
import ReactiveCocoa
/// Responsible for resolving acyclic dependency graphs.
public struct Resolver {
private let versionsForDependency: ProjectIdentifier -> SignalProducer<PinnedVersion, CarthageError>
private let resolvedGitReference: (ProjectIdentifier, String) -> SignalProducer<PinnedVersion, CarthageError>
private let cartfileForDependency: Dependency<PinnedVersion> -> SignalProducer<Cartfile, CarthageError>
/// Instantiates a dependency graph resolver with the given behaviors.
///
/// versionsForDependency - Sends a stream of available versions for a
/// dependency.
/// cartfileForDependency - Loads the Cartfile for a specific version of a
/// dependency.
/// resolvedGitReference - Resolves an arbitrary Git reference to the
/// latest object.
public init(versionsForDependency: ProjectIdentifier -> SignalProducer<PinnedVersion, CarthageError>, cartfileForDependency: Dependency<PinnedVersion> -> SignalProducer<Cartfile, CarthageError>, resolvedGitReference: (ProjectIdentifier, String) -> SignalProducer<PinnedVersion, CarthageError>) {
self.versionsForDependency = versionsForDependency
self.cartfileForDependency = cartfileForDependency
self.resolvedGitReference = resolvedGitReference
}
/// Attempts to determine the latest valid version to use for each dependency
/// specified in the given Cartfile, and all nested dependencies thereof.
///
/// Sends each recursive dependency with its resolved version, in the order
/// that they should be built.
public func resolveDependenciesInCartfile(cartfile: Cartfile) -> SignalProducer<Dependency<PinnedVersion>, CarthageError> {
return nodePermutationsForCartfile(cartfile)
|> map { rootNodes -> SignalProducer<Event<DependencyGraph, CarthageError>, CarthageError> in
return self.graphPermutationsForEachNode(rootNodes, dependencyOf: nil, basedOnGraph: DependencyGraph())
|> promoteErrors(CarthageError.self)
}
|> flatten(.Concat)
// Pass through resolution errors only if we never got
// a valid graph.
|> dematerializeErrorsIfEmpty
|> take(1)
|> map { graph -> SignalProducer<Dependency<PinnedVersion>, CarthageError> in
return SignalProducer(values: graph.orderedNodes)
|> map { node in node.dependencyVersion }
}
|> flatten(.Merge)
}
/// Sends all permutations of valid DependencyNodes, corresponding to the
/// dependencies listed in the given Cartfile, in the order that they should
/// be tried.
///
/// In other words, this will always send arrays equal in length to
/// `cartfile.dependencies`. Each array represents one possible permutation
/// of those dependencies (chosen from among the versions that actually
/// exist for each).
private func nodePermutationsForCartfile(cartfile: Cartfile) -> SignalProducer<[DependencyNode], CarthageError> {
let nodeProducers = cartfile.dependencies.map { dependency -> SignalProducer<DependencyNode, CarthageError> in
let allowedVersions: SignalProducer<PinnedVersion, CarthageError> = {
switch dependency.version {
case let .GitReference(refName):
return self.resolvedGitReference(dependency.project, refName)
default:
return self.versionsForDependency(dependency.project)
|> reduce([]) { $0 + [ $1 ] }
|> map { nodes -> SignalProducer<PinnedVersion, CarthageError> in
if nodes.isEmpty {
return SignalProducer(error: CarthageError.TaggedVersionNotFound(dependency.project))
} else {
return SignalProducer(values: nodes)
}
}
|> flatten(.Merge)
|> filter { dependency.version.satisfiedBy($0) }
}
}()
return allowedVersions
|> map { DependencyNode(project: dependency.project, proposedVersion: $0, versionSpecifier: dependency.version) }
|> reduce([]) { $0 + [ $1 ] }
|> map(sorted)
|> map { nodes -> SignalProducer<DependencyNode, CarthageError> in
if nodes.isEmpty {
return SignalProducer(error: CarthageError.RequiredVersionNotFound(dependency.project, dependency.version))
} else {
return SignalProducer(values: nodes)
}
}
|> flatten(.Concat)
}
return permutations(nodeProducers)
}
/// Sends all possible permutations of `inputGraph` oriented around the
/// dependencies of `node`.
///
/// In other words, this attempts to create one transformed graph for each
/// possible permutation of the dependencies for the given node (chosen from
/// among the verisons that actually exist for each).
private func graphPermutationsForDependenciesOfNode(node: DependencyNode, basedOnGraph inputGraph: DependencyGraph) -> SignalProducer<DependencyGraph, CarthageError> {
return cartfileForDependency(node.dependencyVersion)
|> concat(SignalProducer(value: Cartfile(dependencies: [])))
|> take(1)
|> map { self.nodePermutationsForCartfile($0) }
|> flatten(.Merge)
|> map { dependencyNodes in
return self.graphPermutationsForEachNode(dependencyNodes, dependencyOf: node, basedOnGraph: inputGraph)
|> promoteErrors(CarthageError.self)
}
|> flatten(.Concat)
// Pass through resolution errors only if we never got
// a valid graph.
|> dematerializeErrorsIfEmpty
}
/// Recursively permutes each element in `nodes` and all dependencies
/// thereof, attaching each permutation to `inputGraph` as a dependency of
/// the specified node (or as a root otherwise).
///
/// This is a helper method, and not meant to be called from outside.
private func graphPermutationsForEachNode(nodes: [DependencyNode], dependencyOf: DependencyNode?, basedOnGraph inputGraph: DependencyGraph) -> SignalProducer<Event<DependencyGraph, CarthageError>, NoError> {
return SignalProducer<(DependencyGraph, [DependencyNode]), CarthageError>.try {
let initial: (DependencyGraph, [DependencyNode]) = (inputGraph, [])
var result: Result<(DependencyGraph, [DependencyNode]), CarthageError> = .success(initial)
for node in nodes {
result = result.flatMap { (var graph, var newNodes) in
switch graph.addNode(node, dependencyOf: dependencyOf) {
case let .Success(newNode):
newNodes.append(newNode.value)
let updated = (graph, newNodes)
return .success(updated)
case let .Failure(error):
return .failure(error.value)
}
}
}
return result
}
|> map { graph, nodes -> SignalProducer<DependencyGraph, CarthageError> in
// Each producer represents all evaluations of one subtree.
let graphProducers = nodes.map { node in self.graphPermutationsForDependenciesOfNode(node, basedOnGraph: graph) }
return permutations(graphProducers)
|> map { graphs -> SignalProducer<Event<DependencyGraph, CarthageError>, CarthageError> in
let result: Result<DependencyGraph, CarthageError> = reduce(graphs, .success(inputGraph)) { (result, graph) in
return result.flatMap { mergeGraphs($0, graph) }
}
switch result {
case let .Success(graph):
return SignalProducer(values: [
Event.Next(graph),
Event.Completed
])
case let .Failure(error):
// Discard impossible graphs.
return SignalProducer(value: .Error(error))
}
}
|> flatten(.Concat)
// Pass through resolution errors only if we never got
// a valid graph.
|> dematerializeErrorsIfEmpty
}
|> flatten(.Merge)
|> materialize
}
}
/// A poor person's Set.
private typealias DependencyNodeSet = [DependencyNode: ()]
/// Represents an acyclic dependency graph in which each project appears at most
/// once.
///
/// Dependency graphs can exist in an incomplete state, but will never be
/// inconsistent (i.e., include versions that are known to be invalid given the
/// current graph).
private struct DependencyGraph: Equatable {
/// A full list of all nodes included in the graph.
var allNodes: DependencyNodeSet = [:]
/// All nodes that have dependencies, associated with those lists of
/// dependencies themselves.
var edges: [DependencyNode: DependencyNodeSet] = [:]
/// The root nodes of the graph (i.e., those dependencies that are listed
/// by the top-level project).
var roots: DependencyNodeSet = [:]
/// Returns all of the graph nodes, in the order that they should be built.
var orderedNodes: [DependencyNode] {
return sorted(allNodes.keys) { (lhs, rhs) in
let lhsDependencies = self.edges[lhs]
let rhsDependencies = self.edges[rhs]
if let rhsDependencies = rhsDependencies {
// If the right node has a dependency on the left node, the
// left node needs to be built first (and is thus ordered
// first).
if contains(rhsDependencies.keys, lhs) {
return true
}
}
if let lhsDependencies = lhsDependencies {
// If the left node has a dependency on the right node, the
// right node needs to be built first.
if contains(lhsDependencies.keys, rhs) {
return false
}
}
// If neither node depends on each other, sort the one with the
// fewer dependencies first.
let lhsCount = lhsDependencies?.count ?? 0
let rhsCount = rhsDependencies?.count ?? 0
if lhsCount < rhsCount {
return true
} else if lhsCount > rhsCount {
return false
} else {
// If all else fails, compare names.
return lhs.project.name < rhs.project.name
}
}
}
init() {}
/// Attempts to add the given node to the graph, optionally as a dependency
/// of another.
///
/// If the given node refers to a project which already exists in the graph,
/// this method will attempt to unify the version specifiers of both.
///
/// Returns the node as actually inserted into the graph (which may be
/// different from the node passed in), or an error if this addition would
/// make the graph inconsistent.
mutating func addNode(var node: DependencyNode, dependencyOf: DependencyNode?) -> Result<DependencyNode, CarthageError> {
if let index = allNodes.indexForKey(node) {
let existingNode = allNodes[index].0
if let newSpecifier = intersection(existingNode.versionSpecifier, node.versionSpecifier) {
if newSpecifier.satisfiedBy(existingNode.proposedVersion) {
node = existingNode
node.versionSpecifier = newSpecifier
} else {
return .failure(CarthageError.RequiredVersionNotFound(node.project, newSpecifier))
}
} else {
return .failure(CarthageError.IncompatibleRequirements(node.project, existingNode.versionSpecifier, node.versionSpecifier))
}
} else {
allNodes[node] = ()
}
if let dependencyOf = dependencyOf {
var nodeSet = edges[dependencyOf] ?? DependencyNodeSet()
nodeSet[node] = ()
edges[dependencyOf] = nodeSet
} else {
roots[node] = ()
}
return .success(node)
}
}
private func ==(lhs: DependencyGraph, rhs: DependencyGraph) -> Bool {
if lhs.edges.count != rhs.edges.count || lhs.roots.count != rhs.roots.count {
return false
}
for (edge, leftDeps) in lhs.edges {
if let rightDeps = rhs.edges[edge] {
if leftDeps.count != rightDeps.count {
return false
}
for (dep, _) in leftDeps {
if rightDeps[dep] == nil {
return false
}
}
} else {
return false
}
}
for (root, _) in lhs.roots {
if rhs.roots[root] == nil {
return false
}
}
return true
}
extension DependencyGraph: Printable {
private var description: String {
var str = "Roots:"
for (root, _) in roots {
str += "\n\t\(root)"
}
str += "\n\nEdges:"
for (node, dependencies) in edges {
str += "\n\t\(node.project) ->"
for (dep, _) in dependencies {
str += "\n\t\t\(dep)"
}
}
return str
}
}
/// Attempts to unify two graphs.
///
/// Returns the new graph, or an error if the graphs specify inconsistent
/// versions for one or more dependencies.
private func mergeGraphs(lhs: DependencyGraph, rhs: DependencyGraph) -> Result<DependencyGraph, CarthageError> {
var result: Result<DependencyGraph, CarthageError> = .success(lhs)
for (root, _) in rhs.roots {
result = result.flatMap { (var graph) in
return graph.addNode(root, dependencyOf: nil).map { _ in graph }
}
}
for (node, dependencies) in rhs.edges {
for (dependency, _) in dependencies {
result = result.flatMap { (var graph) in
return graph.addNode(dependency, dependencyOf: node).map { _ in graph }
}
}
}
return result
}
/// A node in, or being considered for, an acyclic dependency graph.
private class DependencyNode: Comparable {
/// The project that this node refers to.
let project: ProjectIdentifier
/// The version of the dependency that this node represents.
///
/// This version is merely "proposed" because it depends on the final
/// resolution of the graph, as well as whether any "better" graphs exist.
let proposedVersion: PinnedVersion
/// The current requirements applied to this dependency.
///
/// This specifier may change as the graph is added to, and the requirements
/// become more stringent.
var versionSpecifier: VersionSpecifier
/// A Dependency equivalent to this node.
var dependencyVersion: Dependency<PinnedVersion> {
return Dependency(project: project, version: proposedVersion)
}
init(project: ProjectIdentifier, proposedVersion: PinnedVersion, versionSpecifier: VersionSpecifier) {
precondition(versionSpecifier.satisfiedBy(proposedVersion))
self.project = project
self.proposedVersion = proposedVersion
self.versionSpecifier = versionSpecifier
}
}
private func <(lhs: DependencyNode, rhs: DependencyNode) -> Bool {
let leftSemantic = SemanticVersion.fromPinnedVersion(lhs.proposedVersion).value ?? SemanticVersion(major: 0, minor: 0, patch: 0)
let rightSemantic = SemanticVersion.fromPinnedVersion(rhs.proposedVersion).value ?? SemanticVersion(major: 0, minor: 0, patch: 0)
// Try higher versions first.
return leftSemantic > rightSemantic
}
private func ==(lhs: DependencyNode, rhs: DependencyNode) -> Bool {
return lhs.project == rhs.project
}
extension DependencyNode: Hashable {
private var hashValue: Int {
return project.hashValue
}
}
extension DependencyNode: Printable {
private var description: String {
return "\(project) @ \(proposedVersion) (restricted to \(versionSpecifier))"
}
}