Maybe use less memory

All CollectingRules implement AnyCollectingRule, which is used to check
whether a linter will perform any collections and only print the
"Collecting" log message if so.

.swiftlint.yml

@@ -4,8 +4,9 @@ included:
 excluded:
   - Tests/SwiftLintFrameworkTests/Resources
 analyzer_rules:
-  - unused_import
-  - unused_private_declaration
+  - unused_declaration
+  # - unused_import
+  # - unused_private_declaration
 opt_in_rules:
   - anyobject_protocol
   - array_init

CHANGELOG.md

@@ -6,7 +6,13 @@
 
 #### Experimental
 
-* None.
+* Add a two-stage `CollectingRule` protocol to support rules that collect data
+  from all files before validating. Collecting rules implement a `collect`
+  method which is called once for every file, before _any_ file is checked for
+  violations. By collecting, rules can be written which validate across
+  multiple files for things like unused declarations.  
+  [Elliott Williams](https://github.com/elliottwilliams)
+  [#2431](https://github.com/realm/SwiftLint/issues/2431)
 
 #### Enhancements
 

Makefile

@@ -62,8 +62,8 @@ test_tsan:
 	swift build --build-tests $(TSAN_SWIFT_BUILD_FLAGS)
 	DYLD_INSERT_LIBRARIES=$(TSAN_LIB) $(TSAN_XCTEST) $(TSAN_TEST_BUNDLE)
 
-write_xcodebuild_log: bootstrap
-	xcodebuild -workspace SwiftLint.xcworkspace -scheme swiftlint > xcodebuild.log
+write_xcodebuild_log:
+	xcodebuild -workspace SwiftLint.xcworkspace -scheme swiftlint clean build-for-testing > xcodebuild.log
 
 analyze: write_xcodebuild_log
 	swift run -c release swiftlint analyze --strict --compiler-log-path xcodebuild.log

Package.resolved

@@ -39,11 +39,11 @@
       },
       {
         "package": "SourceKitten",
-        "repositoryURL": "https://github.com/jpsim/SourceKitten.git",
+        "repositoryURL": "https://github.com/cltnschlosser/SourceKitten.git",
         "state": {
-          "branch": null,
-          "revision": "fd9091759201473aa234c22322a3939615aef59a",
-          "version": "0.23.2"
+          "branch": "cs_sourceKitMemoryLeak2",
+          "revision": "b6c9c6c56a898faabe2671152dfa963bb8d6f5e9",
+          "version": null
         }
       },
       {

Package.swift

@@ -15,7 +15,7 @@ let package = Package(
     ],
     dependencies: [
         .package(url: "https://github.com/Carthage/Commandant.git", .upToNextMinor(from: "0.16.0")),
-        .package(url: "https://github.com/jpsim/SourceKitten.git", from: "0.23.2"),
+        .package(url: "https://github.com/cltnschlosser/SourceKitten.git", .branch("cs_sourceKitMemoryLeak2")),
         .package(url: "https://github.com/jpsim/Yams.git", from: "2.0.0"),
         .package(url: "https://github.com/scottrhoyt/SwiftyTextTable.git", from: "0.9.0"),
     ] + (addCryptoSwift ? [.package(url: "https://github.com/krzyzanowskim/CryptoSwift.git", from: "1.0.0")] : []),

Source/SwiftLintFramework/Extensions/Array+SwiftLint.swift

@@ -45,11 +45,11 @@ extension Array {
             return (copy[0..<pivot], copy[pivot..<count])
     }
 
-    func parallelFlatMap<T>(transform: @escaping ((Element) -> [T])) -> [T] {
+    func parallelFlatMap<T>(transform: (Element) -> [T]) -> [T] {
         return parallelMap(transform: transform).flatMap { $0 }
     }
 
-    func parallelCompactMap<T>(transform: @escaping ((Element) -> T?)) -> [T] {
+    func parallelCompactMap<T>(transform: (Element) -> T?) -> [T] {
         return parallelMap(transform: transform).compactMap { $0 }
     }
 

Source/SwiftLintFramework/Models/Linter.swift

@@ -50,6 +50,7 @@ private extension Rule {
     // As we need the configuration to get custom identifiers.
     // swiftlint:disable:next function_parameter_count
     func lint(file: File, regions: [Region], benchmark: Bool,
+              storage: RuleStorage,
               configuration: Configuration,
               superfluousDisableCommandRule: SuperfluousDisableCommandRule?,
               compilerArguments: [String]) -> LintResult? {
@@ -63,10 +64,10 @@ private extension Rule {
         let ruleTime: (String, Double)?
         if benchmark {
             let start = Date()
-            violations = validate(file: file, compilerArguments: compilerArguments)
+            violations = validate(file: file, using: storage, compilerArguments: compilerArguments)
             ruleTime = (ruleID, -start.timeIntervalSinceNow)
         } else {
-            violations = validate(file: file, compilerArguments: compilerArguments)
+            violations = validate(file: file, using: storage, compilerArguments: compilerArguments)
             ruleTime = nil
         }
 
@@ -107,22 +108,70 @@ private extension Rule {
     }
 }
 
+/// Represents a file that can be linted for style violations and corrections after being collected.
 public struct Linter {
+    public let file: File
+    public var isCollecting: Bool
+    fileprivate let rules: [Rule]
+    fileprivate let cache: LinterCache?
+    fileprivate let configuration: Configuration
+    fileprivate let compilerArguments: [String]
+
+    public init(file: File, configuration: Configuration = Configuration()!, cache: LinterCache? = nil,
+                compilerArguments: [String] = []) {
+        self.file = file
+        self.cache = cache
+        self.configuration = configuration
+        self.compilerArguments = compilerArguments
+        let rules = configuration.rules.filter { rule in
+            if compilerArguments.isEmpty {
+                return !(rule is AnalyzerRule)
+            } else {
+                return rule is AnalyzerRule
+            }
+        }
+        self.rules = rules
+        self.isCollecting = rules.contains(where: { $0 is AnyCollectingRule })
+    }
+
+    /// Returns a linter capable of checking for violations after running each rule's collection step.
+    public func collect(into storage: RuleStorage) -> CollectedLinter {
+        DispatchQueue.concurrentPerform(iterations: rules.count) { idx in
+            rules[idx].collectInfo(for: file, into: storage, compilerArguments: compilerArguments)
+        }
+        return CollectedLinter(from: self)
+    }
+}
+
+/// Represents a file that can compute style violations and corrections for a list of rules.
+///
+/// A `CollectedLinter` is only created after a `Linter` has run its collection steps in `Linter.collect(into:)`.
+public struct CollectedLinter {
     public let file: File
     private let rules: [Rule]
     private let cache: LinterCache?
     private let configuration: Configuration
     private let compilerArguments: [String]
 
-    public var styleViolations: [StyleViolation] {
-        return getStyleViolations().0
+    fileprivate init(from linter: Linter) {
+        file = linter.file
+        rules = linter.rules
+        cache = linter.cache
+        configuration = linter.configuration
+        compilerArguments = linter.compilerArguments
     }
 
-    public var styleViolationsAndRuleTimes: ([StyleViolation], [(id: String, time: Double)]) {
-        return getStyleViolations(benchmark: true)
+    public func styleViolations(using storage: RuleStorage) -> [StyleViolation] {
+        return getStyleViolations(using: storage).0
     }
 
-    private func getStyleViolations(benchmark: Bool = false) -> ([StyleViolation], [(id: String, time: Double)]) {
+    public func styleViolationsAndRuleTimes(using storage: RuleStorage)
+        -> ([StyleViolation], [(id: String, time: Double)]) {
+            return getStyleViolations(using: storage, benchmark: true)
+    }
+
+    private func getStyleViolations(using storage: RuleStorage,
+                                    benchmark: Bool = false) -> ([StyleViolation], [(id: String, time: Double)]) {
         if let cached = cachedStyleViolations(benchmark: benchmark) {
             return cached
         }
@@ -136,6 +185,7 @@ public struct Linter {
         }) as? SuperfluousDisableCommandRule
         let validationResults = rules.parallelCompactMap {
             $0.lint(file: self.file, regions: regions, benchmark: benchmark,
+                    storage: storage,
                     configuration: self.configuration,
                     superfluousDisableCommandRule: superfluousDisableCommandRule,
                     compilerArguments: self.compilerArguments)
@@ -184,29 +234,14 @@ public struct Linter {
         return (cachedViolations, ruleTimes)
     }
 
-    public init(file: File, configuration: Configuration = Configuration()!, cache: LinterCache? = nil,
-                compilerArguments: [String] = []) {
-        self.file = file
-        self.configuration = configuration
-        self.cache = cache
-        self.compilerArguments = compilerArguments
-        self.rules = configuration.rules.filter { rule in
-            if compilerArguments.isEmpty {
-                return !(rule is AnalyzerRule)
-            } else {
-                return rule is AnalyzerRule
-            }
-        }
-    }
-
-    public func correct() -> [Correction] {
+    public func correct(using storage: RuleStorage) -> [Correction] {
         if let violations = cachedStyleViolations()?.0, violations.isEmpty {
             return []
         }
 
         var corrections = [Correction]()
         for rule in rules.compactMap({ $0 as? CorrectableRule }) {
-            let newCorrections = rule.correct(file: file, compilerArguments: compilerArguments)
+            let newCorrections = rule.correct(file: file, using: storage, compilerArguments: compilerArguments)
             corrections += newCorrections
             if !newCorrections.isEmpty {
                 file.invalidateCache()

Source/SwiftLintFramework/Models/MasterRuleList.swift

@@ -162,6 +162,7 @@ public let masterRuleList = RuleList(rules: [
     UnusedCaptureListRule.self,
     UnusedClosureParameterRule.self,
     UnusedControlFlowLabelRule.self,
+    UnusedDeclarationRule.self,
     UnusedEnumeratedRule.self,
     UnusedImportRule.self,
     UnusedOptionalBindingRule.self,

Source/SwiftLintFramework/Models/RuleStorage.swift

@@ -0,0 +1,24 @@
+import Dispatch
+import SourceKittenFramework
+
+public class RuleStorage {
+    private var storage: [ObjectIdentifier: [File: Any]]
+    private let access = DispatchQueue(label: "io.realm.swiftlint.ruleStorageAccess", attributes: .concurrent)
+
+    public init() {
+        storage = [:]
+    }
+
+    func collect<R: CollectingRule>(info: R.FileInfo, for file: File, in rule: R) {
+        let key = ObjectIdentifier(R.self)
+        access.sync(flags: .barrier) {
+            storage[key, default: [:]][file] = info
+        }
+    }
+
+    func collectedInfo<R: CollectingRule>(for rule: R) -> [File: R.FileInfo]? {
+        return access.sync {
+            storage[ObjectIdentifier(R.self)] as? [File: R.FileInfo]
+        }
+    }
+}

Source/SwiftLintFramework/Protocols/Rule.swift

@@ -11,9 +11,17 @@ public protocol Rule {
     func validate(file: File, compilerArguments: [String]) -> [StyleViolation]
     func validate(file: File) -> [StyleViolation]
     func isEqualTo(_ rule: Rule) -> Bool
+
+    // These are called by the linter and are always implemented in extensions.
+    func collectInfo(for file: File, into storage: RuleStorage, compilerArguments: [String])
+    func validate(file: File, using storage: RuleStorage, compilerArguments: [String]) -> [StyleViolation]
 }
 
 extension Rule {
+    public func validate(file: File, using storage: RuleStorage, compilerArguments: [String]) -> [StyleViolation] {
+        return validate(file: file, compilerArguments: compilerArguments)
+    }
+
     public func validate(file: File, compilerArguments: [String]) -> [StyleViolation] {
         return validate(file: file)
     }
@@ -22,6 +30,10 @@ extension Rule {
         return type(of: self).description == type(of: rule).description
     }
 
+    public func collectInfo(for file: File, into storage: RuleStorage, compilerArguments: [String]) {
+        // no-op: only CollectingRules mutate their storage
+    }
+
     internal var cacheDescription: String {
         return (self as? CacheDescriptionProvider)?.cacheDescription ?? configurationDescription
     }
@@ -40,12 +52,18 @@ public protocol ConfigurationProviderRule: Rule {
 public protocol CorrectableRule: Rule {
     func correct(file: File, compilerArguments: [String]) -> [Correction]
     func correct(file: File) -> [Correction]
+
+    // Called by the linter and are always implemented in extensions.
+    func correct(file: File, using storage: RuleStorage, compilerArguments: [String]) -> [Correction]
 }
 
 public extension CorrectableRule {
     func correct(file: File, compilerArguments: [String]) -> [Correction] {
         return correct(file: file)
     }
+    func correct(file: File, using storage: RuleStorage, compilerArguments: [String]) -> [Correction] {
+        return correct(file: file, compilerArguments: compilerArguments)
+    }
 }
 
 public protocol SubstitutionCorrectableRule: CorrectableRule {
@@ -117,7 +135,96 @@ public extension AnalyzerRule where Self: CorrectableRule {
     }
 }
 
-// MARK: - ConfigurationProviderRule conformance to Configurable
+// MARK: - Collecting rules
+
+/// Type-erased protocol used to check whether a rule is collectable.
+public protocol AnyCollectingRule: Rule { }
+
+public protocol CollectingRule: AnyCollectingRule {
+    associatedtype FileInfo
+    func collectInfo(for file: File, compilerArguments: [String]) -> FileInfo
+    func collectInfo(for file: File) -> FileInfo
+    func validate(file: File, collectedInfo: [File: FileInfo], compilerArguments: [String]) -> [StyleViolation]
+    func validate(file: File, collectedInfo: [File: FileInfo]) -> [StyleViolation]
+}
+
+public extension CollectingRule {
+    func collectInfo(for file: File, into storage: RuleStorage, compilerArguments: [String]) {
+        storage.collect(info: collectInfo(for: file, compilerArguments: compilerArguments),
+                        for: file, in: self)
+    }
+    func validate(file: File, using storage: RuleStorage, compilerArguments: [String]) -> [StyleViolation] {
+        guard let info = storage.collectedInfo(for: self) else {
+            queuedFatalError("Attempt to validate a CollectingRule before collecting info for it")
+        }
+        return validate(file: file, collectedInfo: info, compilerArguments: compilerArguments)
+    }
+    func collectInfo(for file: File, compilerArguments: [String]) -> FileInfo {
+        return collectInfo(for: file)
+    }
+    func validate(file: File, collectedInfo: [File: FileInfo], compilerArguments: [String]) -> [StyleViolation] {
+        return validate(file: file, collectedInfo: collectedInfo)
+    }
+    func validate(file: File) -> [StyleViolation] {
+        queuedFatalError("Must call `validate(file:collectedInfo:)` for CollectingRule")
+    }
+    func validate(file: File, compilerArguments: [String]) -> [StyleViolation] {
+        queuedFatalError("Must call `validate(file:collectedInfo:compilerArguments:)` for CollectingRule")
+    }
+}
+
+public extension CollectingRule where Self: AnalyzerRule {
+    func collectInfo(for file: File) -> FileInfo {
+        queuedFatalError(
+            "Must call `collect(infoFor:compilerArguments:)` for AnalyzerRule & CollectingRule"
+        )
+    }
+    func validate(file: File) -> [StyleViolation] {
+        queuedFatalError(
+            "Must call `validate(file:collectedInfo:compilerArguments:)` for AnalyzerRule & CollectingRule"
+        )
+    }
+    func validate(file: File, collectedInfo: [File: FileInfo]) -> [StyleViolation] {
+        queuedFatalError(
+            "Must call `validate(file:collectedInfo:compilerArguments:)` for AnalyzerRule & CollectingRule"
+        )
+    }
+}
+
+public protocol CollectingCorrectableRule: CollectingRule, CorrectableRule {
+    func correct(file: File, collectedInfo: [File: FileInfo], compilerArguments: [String]) -> [Correction]
+    func correct(file: File, collectedInfo: [File: FileInfo]) -> [Correction]
+}
+
+public extension CollectingCorrectableRule {
+    func correct(file: File, collectedInfo: [File: FileInfo], compilerArguments: [String]) -> [Correction] {
+        return correct(file: file, collectedInfo: collectedInfo)
+    }
+    func correct(file: File, using storage: RuleStorage, compilerArguments: [String]) -> [Correction] {
+        guard let info = storage.collectedInfo(for: self) else {
+            queuedFatalError("Attempt to correct a CollectingRule before collecting info for it")
+        }
+        return correct(file: file, collectedInfo: info, compilerArguments: compilerArguments)
+    }
+    func correct(file: File) -> [Correction] {
+        queuedFatalError("Must call `correct(file:collectedInfo:)` for AnalyzerRule")
+    }
+    func correct(file: File, compilerArguments: [String]) -> [Correction] {
+        queuedFatalError("Must call `correct(file:collectedInfo:compilerArguments:)` for AnalyzerRule")
+    }
+}
+
+public extension CollectingCorrectableRule where Self: AnalyzerRule {
+    func correct(file: File) -> [Correction] {
+        queuedFatalError("Must call `correct(file:collectedInfo:compilerArguments:)` for AnalyzerRule")
+    }
+    func correct(file: File, compilerArguments: [String]) -> [Correction] {
+        queuedFatalError("Must call `correct(file:collectedInfo:compilerArguments:)` for AnalyzerRule")
+    }
+    func correct(file: File, collectedInfo: [File: FileInfo]) -> [Correction] {
+        queuedFatalError("Must call `correct(file:collectedInfo:compilerArguments:)` for AnalyzerRule")
+    }
+}
 
 public extension ConfigurationProviderRule {
     init(configuration: Any) throws {

Source/SwiftLintFramework/Protocols/RuleConfiguration.swift

@@ -5,12 +5,6 @@ public protocol RuleConfiguration {
     func isEqualTo(_ ruleConfiguration: RuleConfiguration) -> Bool
 }
 
-extension RuleConfiguration {
-    internal var cacheDescription: String {
-        return (self as? CacheDescriptionProvider)?.cacheDescription ?? consoleDescription
-    }
-}
-
 public extension RuleConfiguration where Self: Equatable {
     func isEqualTo(_ ruleConfiguration: RuleConfiguration) -> Bool {
         return self == ruleConfiguration as? Self

Source/SwiftLintFramework/Rules/Lint/UnusedDeclarationRule.swift

@@ -0,0 +1,277 @@
+import Foundation
+import SourceKittenFramework
+
+public struct UnusedDeclarationRule: AutomaticTestableRule, ConfigurationProviderRule, AnalyzerRule, CollectingRule {
+    public struct FileUSRs {
+        var referenced: Set<String>
+        var declared: [(usr: String, nameOffset: Int)]
+        var testCaseUSRs: Set<String>
+    }
+
+    public typealias FileInfo = FileUSRs
+
+    public var configuration = UnusedDeclarationConfiguration(severity: .error, includePublicAndOpen: false)
+
+    public init() {}
+
+    public static let description = RuleDescription(
+        identifier: "unused_declaration",
+        name: "Unused Declaration",
+        description: "Declarations should be referenced at least once within all files linted.",
+        kind: .lint,
+        nonTriggeringExamples: [
+            """
+            let kConstant = 0
+            _ = kConstant
+            """,
+            """
+            struct Item {}
+            struct ResponseModel: Codable {
+                let items: [Item]
+
+                enum CodingKeys: String, CodingKey {
+                    case items = "ResponseItems"
+                }
+            }
+
+            _ = ResponseModel(items: [Item()]).items
+            """,
+            """
+            class ResponseModel {
+                @objc func foo() {
+                }
+            }
+            _ = ResponseModel()
+            """
+        ],
+        triggeringExamples: [
+            """
+            let ↓kConstant = 0
+            """,
+            """
+            struct ↓ResponseModel: Codable {
+                let ↓items: [Item]
+
+                enum ↓CodingKeys: String {
+                    case items = "ResponseItems"
+                }
+            }
+            """,
+            """
+            class ↓ResponseModel {
+                func ↓foo() {
+                }
+            }
+            """
+        ],
+        requiresFileOnDisk: true
+    )
+
+    public func collectInfo(for file: File, compilerArguments: [String]) -> UnusedDeclarationRule.FileUSRs {
+        guard !compilerArguments.isEmpty else {
+            queuedPrintError("""
+                Attempted to lint file at path '\(file.path ?? "...")' with the \
+                \(type(of: self).description.identifier) rule without any compiler arguments.
+                """)
+            return FileUSRs(referenced: [], declared: [], testCaseUSRs: [])
+        }
+
+        let allCursorInfo = file.allCursorInfo(compilerArguments: compilerArguments)
+        return FileUSRs(referenced: Set(File.referencedUSRs(allCursorInfo: allCursorInfo)),
+                        declared: File.declaredUSRs(allCursorInfo: allCursorInfo,
+                                                    includePublicAndOpen: configuration.includePublicAndOpen),
+                        testCaseUSRs: File.testCaseUSRs(allCursorInfo: allCursorInfo))
+    }
+
+    public func validate(file: File, collectedInfo: [File: UnusedDeclarationRule.FileUSRs],
+                         compilerArguments: [String]) -> [StyleViolation] {
+        let allReferencedUSRs = collectedInfo.values.reduce(into: Set()) { $0.formUnion($1.referenced) }
+        let allTestCaseUSRs = collectedInfo.values.reduce(into: Set()) { $0.formUnion($1.testCaseUSRs) }
+        return violationOffsets(in: file, compilerArguments: compilerArguments,
+                                declaredUSRs: collectedInfo[file]?.declared ?? [],
+                                allReferencedUSRs: allReferencedUSRs,
+                                allTestCaseUSRs: allTestCaseUSRs)
+            .map {
+                StyleViolation(ruleDescription: type(of: self).description,
+                               severity: configuration.severity,
+                               location: Location(file: file, byteOffset: $0))
+            }
+    }
+
+    private func violationOffsets(in file: File, compilerArguments: [String],
+                                  declaredUSRs: [(usr: String, nameOffset: Int)],
+                                  allReferencedUSRs: Set<String>,
+                                  allTestCaseUSRs: Set<String>) -> [Int] {
+        // Unused declarations are:
+        // 1. all declarations
+        // 2. minus all references
+        // 3. minus all XCTestCase subclasses
+        // 4. minus all XCTest test functions
+        let unusedDeclarations = declaredUSRs
+            .filter { !allReferencedUSRs.contains($0.usr) }
+            .filter { !allTestCaseUSRs.contains($0.usr) }
+            .filter { declaredUSR in
+                return !allTestCaseUSRs.contains(where: { testCaseUSR in
+                    return declaredUSR.usr.hasPrefix(testCaseUSR + "(im)test") ||
+                        declaredUSR.usr.hasPrefix(
+                            testCaseUSR.replacingOccurrences(of: "@M@", with: "@CM@") + "(im)test"
+                        )
+                })
+            }
+        return unusedDeclarations.map { $0.nameOffset }
+    }
+}
+
+// MARK: - File Extensions
+
+private extension File {
+    func allCursorInfo(compilerArguments: [String]) -> [[String: SourceKitRepresentable]] {
+        guard let path = path, let editorOpen = try? Request.editorOpen(file: self).sendIfNotDisabled() else {
+            return []
+        }
+
+        return syntaxMap.tokens.compactMap { token in
+            guard let kind = SyntaxKind(rawValue: token.type), !syntaxKindsToSkip.contains(kind) else {
+                return nil
+            }
+
+            let offset = Int64(token.offset)
+            let request = Request.cursorInfo(file: path, offset: offset, arguments: compilerArguments)
+            guard var cursorInfo = try? request.sendIfNotDisabled() else {
+                return nil
+            }
+
+            if let acl = File.aclAtOffset(offset, substructureElement: editorOpen) {
+                cursorInfo["key.accessibility"] = acl
+            }
+            cursorInfo["swiftlint.offset"] = offset
+            return cursorInfo
+        }
+    }
+
+    static func declaredUSRs(allCursorInfo: [[String: SourceKitRepresentable]], includePublicAndOpen: Bool)
+        -> [(usr: String, nameOffset: Int)] {
+        return allCursorInfo.compactMap { cursorInfo in
+            return declaredUSRAndOffset(cursorInfo: cursorInfo, includePublicAndOpen: includePublicAndOpen)
+        }
+    }
+
+    static func referencedUSRs(allCursorInfo: [[String: SourceKitRepresentable]]) -> [String] {
+        return allCursorInfo.compactMap(referencedUSR)
+    }
+
+    static func testCaseUSRs(allCursorInfo: [[String: SourceKitRepresentable]]) -> Set<String> {
+        return Set(allCursorInfo.compactMap(testCaseUSR))
+    }
+
+    private static func declaredUSRAndOffset(cursorInfo: [String: SourceKitRepresentable], includePublicAndOpen: Bool)
+        -> (usr: String, nameOffset: Int)? {
+        if let offset = cursorInfo["swiftlint.offset"] as? Int64,
+            let usr = cursorInfo["key.usr"] as? String,
+            let kind = (cursorInfo["key.kind"] as? String).flatMap(SwiftDeclarationKind.init(rawValue:)),
+            !declarationKindsToSkip.contains(kind),
+            let acl = (cursorInfo["key.accessibility"] as? String).flatMap(AccessControlLevel.init(rawValue:)),
+            includePublicAndOpen || [.internal, .private, .fileprivate].contains(acl) {
+            // Skip declarations marked as @IBOutlet, @IBAction or @objc
+            // since those might not be referenced in code, but only dynamically (e.g. Interface Builder)
+            if let annotatedDecl = cursorInfo["key.annotated_decl"] as? String,
+                ["@IBOutlet", "@IBAction", "@objc", "@IBInspectable"].contains(where: annotatedDecl.contains) {
+                return nil
+            }
+
+            // Classes marked as @UIApplicationMain are used by the operating system as the entry point into the app.
+            if let annotatedDecl = cursorInfo["key.annotated_decl"] as? String,
+                annotatedDecl.contains("@UIApplicationMain") {
+                return nil
+            }
+
+            // Skip declarations that override another. This works for both subclass overrides &
+            // protocol extension overrides.
+            if cursorInfo["key.overrides"] != nil {
+                return nil
+            }
+
+            // Sometimes default protocol implementations don't have `key.overrides` set but they do have
+            // `key.related_decls`.
+            if cursorInfo["key.related_decls"] != nil {
+                return nil
+            }
+
+            // Skip CodingKeys as they are used
+            if kind == .enum,
+                cursorInfo.name == "CodingKeys",
+                let annotatedDecl = cursorInfo["key.annotated_decl"] as? String,
+                annotatedDecl.contains("usr=\"s:s9CodingKeyP\">CodingKey<") {
+                return nil
+            }
+
+            return (usr, Int(offset))
+        }
+
+        return nil
+    }
+
+    private static func referencedUSR(cursorInfo: [String: SourceKitRepresentable]) -> String? {
+        if let usr = cursorInfo["key.usr"] as? String,
+            let kind = cursorInfo["key.kind"] as? String,
+            kind.contains("source.lang.swift.ref") {
+            return usr
+        }
+
+        return nil
+    }
+
+    private static func testCaseUSR(cursorInfo: [String: SourceKitRepresentable]) -> String? {
+        if let kind = (cursorInfo["key.kind"] as? String).flatMap(SwiftDeclarationKind.init(rawValue:)),
+            kind == .class,
+            let annotatedDecl = cursorInfo["key.annotated_decl"] as? String,
+            annotatedDecl.contains("<Type usr=\"c:objc(cs)XCTestCase\">XCTestCase</Type>"),
+            let usr = cursorInfo["key.usr"] as? String {
+            return usr
+        }
+
+        return nil
+    }
+
+    private static func aclAtOffset(_ offset: Int64, substructureElement: [String: SourceKitRepresentable]) -> String? {
+        if let nameOffset = substructureElement["key.nameoffset"] as? Int64,
+            nameOffset == offset,
+            let acl = substructureElement["key.accessibility"] as? String {
+            return acl
+        }
+        if let substructure = substructureElement[SwiftDocKey.substructure.rawValue] as? [SourceKitRepresentable] {
+            let nestedSubstructure = substructure.compactMap({ $0 as? [String: SourceKitRepresentable] })
+            for child in nestedSubstructure {
+                if let acl = File.aclAtOffset(offset, substructureElement: child) {
+                    return acl
+                }
+            }
+        }
+        return nil
+    }
+}
+
+// Skip initializers, deinit, enum cases and subscripts since we can't reliably detect if they're used.
+private let declarationKindsToSkip: Set<SwiftDeclarationKind> = [
+    .functionConstructor,
+    .functionDestructor,
+    .enumelement,
+    .functionSubscript
+]
+
+/// Skip syntax kinds that won't respond to cursor info requests.
+private let syntaxKindsToSkip: Set<SyntaxKind> = [
+    .attributeBuiltin,
+    .attributeID,
+    .comment,
+    .commentMark,
+    .commentURL,
+    .buildconfigID,
+    .buildconfigKeyword,
+    .docComment,
+    .docCommentField,
+    .keyword,
+    .number,
+    .string,
+    .stringInterpolationAnchor
+]

Source/SwiftLintFramework/Rules/RuleConfigurations/UnusedDeclarationConfiguration.swift

@@ -0,0 +1,43 @@
+private enum ConfigurationKey: String {
+    case severity = "severity"
+    case includePublicAndOpen = "include_public_and_open"
+}
+
+public struct UnusedDeclarationConfiguration: RuleConfiguration, Equatable {
+    private(set) var includePublicAndOpen: Bool
+    private(set) var severity: ViolationSeverity
+
+    public var consoleDescription: String {
+        return "\(ConfigurationKey.severity.rawValue): \(severity.rawValue), " +
+            "\(ConfigurationKey.includePublicAndOpen.rawValue): \(includePublicAndOpen)"
+    }
+
+    public init(severity: ViolationSeverity, includePublicAndOpen: Bool) {
+        self.includePublicAndOpen = includePublicAndOpen
+        self.severity = severity
+    }
+
+    public mutating func apply(configuration: Any) throws {
+        guard let configDict = configuration as? [String: Any], !configDict.isEmpty else {
+            throw ConfigurationError.unknownConfiguration
+        }
+
+        for (string, value) in configDict {
+            guard let key = ConfigurationKey(rawValue: string) else {
+                throw ConfigurationError.unknownConfiguration
+            }
+            switch (key, value) {
+            case (.severity, let stringValue as String):
+                if let severityValue = ViolationSeverity(rawValue: stringValue) {
+                    severity = severityValue
+                } else {
+                    throw ConfigurationError.unknownConfiguration
+                }
+            case (.includePublicAndOpen, let boolValue as Bool):
+                includePublicAndOpen = boolValue
+            default:
+                throw ConfigurationError.unknownConfiguration
+            }
+        }
+    }
+}

Source/swiftlint/Commands/AnalyzeCommand.swift

@@ -16,8 +16,10 @@ struct AnalyzeCommand: CommandProtocol {
     }
 
     private func autocorrect(_ options: LintOrAnalyzeOptions) -> Result<(), CommandantError<()>> {
-        return Configuration(options: options).visitLintableFiles(options: options, cache: nil) { linter in
-            let corrections = linter.correct()
+        let storage = RuleStorage()
+        let configuration = Configuration(options: options)
+        return configuration.visitLintableFiles(options: options, cache: nil, storage: storage) { linter in
+            let corrections = linter.correct(using: storage)
             if !corrections.isEmpty && !options.quiet {
                 let correctionLogs = corrections.map({ $0.consoleDescription })
                 queuedPrint(correctionLogs.joined(separator: "\n"))

Source/swiftlint/Commands/AutoCorrectCommand.swift

@@ -8,8 +8,9 @@ struct AutoCorrectCommand: CommandProtocol {
 
     func run(_ options: AutoCorrectOptions) -> Result<(), CommandantError<()>> {
         let configuration = Configuration(options: options)
-        let visitor = options.visitor(with: configuration)
-        return configuration.visitLintableFiles(with: visitor).flatMap { files in
+        let storage = RuleStorage()
+        let visitor = options.visitor(with: configuration, storage: storage)
+        return configuration.visitLintableFiles(with: visitor, storage: storage).flatMap { files in
             if !options.quiet {
                 let pluralSuffix = { (collection: [Any]) -> String in
                     return collection.count != 1 ? "s" : ""
@@ -63,7 +64,7 @@ struct AutoCorrectOptions: OptionsProtocol {
             <*> mode <| pathsArgument(action: "correct")
     }
 
-    fileprivate func visitor(with configuration: Configuration) -> LintableFilesVisitor {
+    fileprivate func visitor(with configuration: Configuration, storage: RuleStorage) -> LintableFilesVisitor {
         let cache = ignoreCache ? nil : LinterCache(configuration: configuration)
         return LintableFilesVisitor(paths: paths, action: "Correcting", useSTDIN: false, quiet: quiet,
                                     useScriptInputFiles: useScriptInputFiles, forceExclude: forceExclude, cache: cache,
@@ -76,7 +77,7 @@ struct AutoCorrectOptions: OptionsProtocol {
                     linter.format(useTabs: false, indentWidth: count)
                 }
             }
-            let corrections = linter.correct()
+            let corrections = linter.correct(using: storage)
             if !corrections.isEmpty && !self.quiet {
                 let correctionLogs = corrections.map({ $0.consoleDescription })
                 queuedPrint(correctionLogs.joined(separator: "\n"))

Source/swiftlint/Extensions/Array+SwiftLint.swift

@@ -0,0 +1 @@
+../../SwiftLintFramework/Extensions/Array+SwiftLint.swift

Source/swiftlint/Extensions/Configuration+CommandLine.swift

@@ -45,14 +45,18 @@ private func scriptInputFiles() -> Result<[File], CommandantError<()>> {
 }
 
 #if os(Linux)
-private func autoreleasepool(block: () -> Void) { block() }
+private func autoreleasepool<T>(block: () -> T) -> T { return block() }
 #endif
 
 extension Configuration {
-    func visitLintableFiles(with visitor: LintableFilesVisitor) -> Result<[File], CommandantError<()>> {
-        return getFiles(with: visitor)
-            .flatMap { groupFiles($0, visitor: visitor) }
-            .flatMap { visit(filesPerConfiguration: $0, visitor: visitor) }
+    func visitLintableFiles(with visitor: LintableFilesVisitor, storage: RuleStorage)
+        -> Result<[File], CommandantError<()>> {
+            return getFiles(with: visitor)
+                .flatMap { groupFiles($0, visitor: visitor) }
+                .map { linters(for: $0, visitor: visitor) }
+                .map { ($0, $0.duplicateFileNames) }
+                .map { collect(linters: $0.0, visitor: visitor, storage: storage, duplicateFileNames: $0.1) }
+                .map { visit(linters: $0.0, visitor: visitor, storage: storage, duplicateFileNames: $0.1) }
     }
 
     private func groupFiles(_ files: [File],
@@ -82,29 +86,31 @@ extension Configuration {
         return .success(groupedFiles)
     }
 
-    private func outputFilename(for path: NSString, in root: NSString, duplicateFileNames: Set<String>) -> String {
-        let basename = path.lastPathComponent
+    private func outputFilename(for path: String, duplicateFileNames: Set<String>) -> String {
+        guard !duplicateFileNames.isEmpty else {
+            return path
+        }
+
+        let root = self.rootPath ?? FileManager.default.currentDirectoryPath.bridge().standardizingPath
+        let basename = path.bridge().lastPathComponent
         if !duplicateFileNames.contains(basename) {
             return basename
         }
 
-        var pathComponents = path.pathComponents
-        for component in root.pathComponents where pathComponents.first == component {
+        var pathComponents = path.bridge().pathComponents
+        for component in root.bridge().pathComponents where pathComponents.first == component {
             pathComponents.removeFirst()
         }
 
         return pathComponents.joined(separator: "/")
     }
 
-    private func visit(filesPerConfiguration: [Configuration: [File]],
-                       visitor: LintableFilesVisitor) -> Result<[File], CommandantError<()>> {
-        var fileIndex = 0
+    private func linters(for filesPerConfiguration: [Configuration: [File]],
+                         visitor: LintableFilesVisitor) -> [Linter] {
         let fileCount = filesPerConfiguration.reduce(0) { $0 + $1.value.count }
-        let root = FileManager.default.currentDirectoryPath.bridge().standardizingPath.bridge()
-        var filesAndConfigurations = [(File, Configuration)]()
-        var allFileNames = Set<String>()
-        var duplicateFileNames = Set<String>()
-        filesAndConfigurations.reserveCapacity(fileCount)
+
+        var linters = [Linter]()
+        linters.reserveCapacity(fileCount)
         for (config, files) in filesPerConfiguration {
             let newConfig: Configuration
             if visitor.cache != nil {
@@ -112,33 +118,79 @@ extension Configuration {
             } else {
                 newConfig = config
             }
-            filesAndConfigurations += files.map { ($0, newConfig) }
-            for file in files {
-                if let filename = file.path?.bridge().lastPathComponent {
-                    if allFileNames.contains(filename) {
-                        duplicateFileNames.insert(filename)
-                    }
+            linters += files.map { visitor.linter(forFile: $0, configuration: newConfig) }
+        }
+        return linters
+    }
 
-                    allFileNames.insert(filename)
+    private func collect(linters: [Linter],
+                         visitor: LintableFilesVisitor,
+                         storage: RuleStorage,
+                         duplicateFileNames: Set<String>) -> ([CollectedLinter], Set<String>) {
+        var collected = 0
+        let total = linters.filter({ $0.isCollecting }).count
+        let collect = { (linter: Linter) -> CollectedLinter? in
+            let skipFile = visitor.shouldSkipFile(atPath: linter.file.path)
+            if !visitor.quiet, linter.isCollecting, let filePath = linter.file.path {
+                let outputFilename = self.outputFilename(for: filePath, duplicateFileNames: duplicateFileNames)
+                let increment = {
+                    collected += 1
+                    if skipFile {
+                        queuedPrintError("""
+                            Skipping '\(outputFilename)' (\(collected)/\(total)) \
+                            because its compiler arguments could not be found
+                            """)
+                    } else {
+                        queuedPrintError("Collecting '\(outputFilename)' (\(collected)/\(total))")
+                    }
+                }
+                if visitor.parallel {
+                    indexIncrementerQueue.sync(execute: increment)
+                } else {
+                    increment()
                 }
             }
-        }
-        let visit = { (file: File, configuration: Configuration) in
-            let printableFileName = (file.path?.bridge()).map { path in
-                self.outputFilename(for: path, in: root, duplicateFileNames: duplicateFileNames)
+
+            guard !skipFile else {
+                return nil
             }
-            visitor.visit(file: file, config: configuration, outputFileName: printableFileName,
-                          incrementIndex: { fileIndex += 1 }, progress: { "(\(fileIndex)/\(fileCount))" })
-        }
-        if visitor.parallel {
-            DispatchQueue.concurrentPerform(iterations: fileCount) { index in
-                let (file, config) = filesAndConfigurations[index]
-                visit(file, config)
+
+            return autoreleasepool {
+                linter.collect(into: storage)
             }
-        } else {
-            filesAndConfigurations.forEach(visit)
         }
-        return .success(filesAndConfigurations.compactMap({ $0.0 }))
+
+        let collectedLinters = visitor.parallel ?
+            linters.parallelCompactMap(transform: collect) :
+            linters.compactMap(collect)
+        return (collectedLinters, duplicateFileNames)
+    }
+
+    private func visit(linters: [CollectedLinter],
+                       visitor: LintableFilesVisitor,
+                       storage: RuleStorage,
+                       duplicateFileNames: Set<String>) -> [File] {
+        var visited = 0
+        let visit = { (linter: CollectedLinter) -> File in
+            if !visitor.quiet, let filePath = linter.file.path {
+                let outputFilename = self.outputFilename(for: filePath, duplicateFileNames: duplicateFileNames)
+                let increment = {
+                    visited += 1
+                    queuedPrintError("\(visitor.action) '\(outputFilename)' (\(visited)/\(linters.count))")
+                }
+                if visitor.parallel {
+                    indexIncrementerQueue.sync(execute: increment)
+                } else {
+                    increment()
+                }
+            }
+
+            autoreleasepool {
+                visitor.block(linter)
+            }
+            return linter.file
+        }
+        return visitor.parallel ? linters.parallelMap(transform: visit) : linters.map(visit)
     }
 
     fileprivate func getFiles(with visitor: LintableFilesVisitor) -> Result<[File], CommandantError<()>> {
@@ -189,9 +241,11 @@ extension Configuration {
                   cachePath: cachePath)
     }
 
-    func visitLintableFiles(options: LintOrAnalyzeOptions, cache: LinterCache? = nil,
-                            visitorBlock: @escaping (Linter) -> Void) -> Result<[File], CommandantError<()>> {
-        return LintableFilesVisitor.create(options, cache: cache, block: visitorBlock).flatMap(visitLintableFiles)
+    func visitLintableFiles(options: LintOrAnalyzeOptions, cache: LinterCache? = nil, storage: RuleStorage,
+                            visitorBlock: @escaping (CollectedLinter) -> Void) -> Result<[File], CommandantError<()>> {
+        return LintableFilesVisitor.create(options, cache: cache, block: visitorBlock).flatMap({ visitor in
+            visitLintableFiles(with: visitor, storage: storage)
+        })
     }
 
     // MARK: AutoCorrect Command
@@ -213,34 +267,22 @@ private func isConfigOptional() -> Bool {
     return !CommandLine.arguments.contains("--config")
 }
 
-private extension LintableFilesVisitor {
-    func visit(file: File, config: Configuration, outputFileName: String?, incrementIndex: @escaping () -> Void,
-               progress: @escaping () -> String) {
-        let skipFile = shouldSkipFile(atPath: file.path)
-        if !quiet, let outputFileName = outputFileName {
-            let increment = {
-                incrementIndex()
-                if skipFile {
-                    queuedPrintError("""
-                        Skipping '\(outputFileName)' \(progress()) because its compiler arguments could not be found
-                        """)
-                } else {
-                    queuedPrintError("\(self.action) '\(outputFileName)' \(progress())")
+private struct DuplicateCollector {
+    var all = Set<String>()
+    var duplicates = Set<String>()
+}
+
+private extension Collection where Element == Linter {
+    var duplicateFileNames: Set<String> {
+        let collector = reduce(into: DuplicateCollector()) { result, linter in
+            if let filename = linter.file.path?.bridge().lastPathComponent {
+                if result.all.contains(filename) {
+                    result.duplicates.insert(filename)
                 }
-            }
-            if parallel {
-                indexIncrementerQueue.sync(execute: increment)
-            } else {
-                increment()
+
+                result.all.insert(filename)
             }
         }
-
-        guard !skipFile else {
-            return
-        }
-
-        autoreleasepool {
-            block(linter(forFile: file, configuration: config))
-        }
+        return collector.duplicates
     }
 }

Source/swiftlint/Helpers/LintOrAnalyzeCommand.swift

@@ -23,15 +23,16 @@ struct LintOrAnalyzeCommand {
         var fileBenchmark = Benchmark(name: "files")
         var ruleBenchmark = Benchmark(name: "rules")
         var violations = [StyleViolation]()
+        let storage = RuleStorage()
         let configuration = Configuration(options: options)
         let reporter = reporterFrom(optionsReporter: options.reporter, configuration: configuration)
         let cache = options.ignoreCache ? nil : LinterCache(configuration: configuration)
         let visitorMutationQueue = DispatchQueue(label: "io.realm.swiftlint.lintVisitorMutation")
-        return configuration.visitLintableFiles(options: options, cache: cache) { linter in
+        return configuration.visitLintableFiles(options: options, cache: cache, storage: storage) { linter in
             let currentViolations: [StyleViolation]
             if options.benchmark {
                 let start = Date()
-                let (violationsBeforeLeniency, currentRuleTimes) = linter.styleViolationsAndRuleTimes
+                let (violationsBeforeLeniency, currentRuleTimes) = linter.styleViolationsAndRuleTimes(using: storage)
                 currentViolations = applyLeniency(options: options, violations: violationsBeforeLeniency)
                 visitorMutationQueue.sync {
                     fileBenchmark.record(file: linter.file, from: start)
@@ -39,7 +40,7 @@ struct LintOrAnalyzeCommand {
                     violations += currentViolations
                 }
             } else {
-                currentViolations = applyLeniency(options: options, violations: linter.styleViolations)
+                currentViolations = applyLeniency(options: options, violations: linter.styleViolations(using: storage))
                 visitorMutationQueue.sync {
                     violations += currentViolations
                 }

Source/swiftlint/Helpers/LintableFilesVisitor.swift

@@ -19,10 +19,10 @@ struct LintableFilesVisitor {
     let cache: LinterCache?
     let parallel: Bool
     let mode: LintOrAnalyzeModeWithCompilerArguments
-    let block: (Linter) -> Void
+    let block: (CollectedLinter) -> Void
 
     init(paths: [String], action: String, useSTDIN: Bool, quiet: Bool, useScriptInputFiles: Bool, forceExclude: Bool,
-         cache: LinterCache?, parallel: Bool, block: @escaping (Linter) -> Void) {
+         cache: LinterCache?, parallel: Bool, block: @escaping (CollectedLinter) -> Void) {
         self.paths = paths
         self.action = action
         self.useSTDIN = useSTDIN
@@ -37,7 +37,7 @@ struct LintableFilesVisitor {
 
     private init(paths: [String], action: String, useSTDIN: Bool, quiet: Bool, useScriptInputFiles: Bool,
                  forceExclude: Bool, cache: LinterCache?, compilerLogContents: String,
-                 block: @escaping (Linter) -> Void) {
+                 block: @escaping (CollectedLinter) -> Void) {
         self.paths = paths
         self.action = action
         self.useSTDIN = useSTDIN
@@ -56,7 +56,7 @@ struct LintableFilesVisitor {
         self.block = block
     }
 
-    static func create(_ options: LintOrAnalyzeOptions, cache: LinterCache?, block: @escaping (Linter) -> Void)
+    static func create(_ options: LintOrAnalyzeOptions, cache: LinterCache?, block: @escaping (CollectedLinter) -> Void)
         -> Result<LintableFilesVisitor, CommandantError<()>> {
         let compilerLogContents: String
         if options.mode == .lint {

SwiftLint.xcodeproj/project.pbxproj

@@ -35,6 +35,9 @@
 		1F11B3CF1C252F23002E8FA8 /* ClosingBraceRule.swift in Sources */ = {isa = PBXBuildFile; fileRef = 1F11B3CE1C252F23002E8FA8 /* ClosingBraceRule.swift */; };
 		24B4DF0D1D6DFDE90097803B /* RedundantNilCoalescingRule.swift in Sources */ = {isa = PBXBuildFile; fileRef = 24B4DF0B1D6DFA370097803B /* RedundantNilCoalescingRule.swift */; };
 		24E17F721B14BB3F008195BE /* File+Cache.swift in Sources */ = {isa = PBXBuildFile; fileRef = 24E17F701B1481FF008195BE /* File+Cache.swift */; };
+		260F66A0225C5B6D00407CF5 /* CollectingRuleTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 260F669F225C5B6D00407CF5 /* CollectingRuleTests.swift */; };
+		264E080F2248BA2800ADC4C5 /* RuleStorage.swift in Sources */ = {isa = PBXBuildFile; fileRef = 264E080E2248BA2800ADC4C5 /* RuleStorage.swift */; };
+		26CE462D228532CD00264485 /* Array+SwiftLint.swift in Sources */ = {isa = PBXBuildFile; fileRef = 26CE462C228532CD00264485 /* Array+SwiftLint.swift */; };
 		287F8B642230843000BDC504 /* NSLocalizedStringRequireBundleRule.swift in Sources */ = {isa = PBXBuildFile; fileRef = 287F8B62223083ED00BDC504 /* NSLocalizedStringRequireBundleRule.swift */; };
 		2882895F222975D00037CF5F /* NSObjectPreferIsEqualRule.swift in Sources */ = {isa = PBXBuildFile; fileRef = 2882895B22287C9C0037CF5F /* NSObjectPreferIsEqualRule.swift */; };
 		288289602229776C0037CF5F /* NSObjectPreferIsEqualRuleExamples.swift in Sources */ = {isa = PBXBuildFile; fileRef = 2882895D22287E2C0037CF5F /* NSObjectPreferIsEqualRuleExamples.swift */; };
@@ -174,6 +177,7 @@
 		85DA81321D6B471000951BC4 /* MarkRule.swift in Sources */ = {isa = PBXBuildFile; fileRef = 856651A61D6B395F005E6B29 /* MarkRule.swift */; };
 		8B01E4FD20A41C8700C9233E /* FunctionParameterCountConfiguration.swift in Sources */ = {isa = PBXBuildFile; fileRef = 8B01E4FB20A4183C00C9233E /* FunctionParameterCountConfiguration.swift */; };
 		8B01E50220A4349100C9233E /* FunctionParameterCountRuleTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 8B01E4FF20A4340A00C9233E /* FunctionParameterCountRuleTests.swift */; };
+		8F0856EB22DA8508001FF4D4 /* UnusedDeclarationRule.swift in Sources */ = {isa = PBXBuildFile; fileRef = 8F0856EA22DA8508001FF4D4 /* UnusedDeclarationRule.swift */; };
 		8F2CC1CB20A6A070006ED34F /* FileNameConfiguration.swift in Sources */ = {isa = PBXBuildFile; fileRef = 8F2CC1CA20A6A070006ED34F /* FileNameConfiguration.swift */; };
 		8F2CC1CD20A6A189006ED34F /* FileNameRuleTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 8F2CC1CC20A6A189006ED34F /* FileNameRuleTests.swift */; };
 		8F6AA75B211905B8009BA28A /* LintableFilesVisitor.swift in Sources */ = {isa = PBXBuildFile; fileRef = 8F6AA75A211905B8009BA28A /* LintableFilesVisitor.swift */; };
@@ -186,6 +190,7 @@
 		8FD216CC205584AF008ED13F /* CharacterSet+SwiftLint.swift in Sources */ = {isa = PBXBuildFile; fileRef = 8FD216CB205584AF008ED13F /* CharacterSet+SwiftLint.swift */; };
 		8FDF482C2122476D00521605 /* AnalyzeCommand.swift in Sources */ = {isa = PBXBuildFile; fileRef = 8FDF482B2122476D00521605 /* AnalyzeCommand.swift */; };
 		8FDF482E21234BFF00521605 /* LintOrAnalyzeCommand.swift in Sources */ = {isa = PBXBuildFile; fileRef = 8FDF482D21234BFF00521605 /* LintOrAnalyzeCommand.swift */; };
+		8FE3CCBC22DBF8D000B8EA87 /* UnusedDeclarationConfiguration.swift in Sources */ = {isa = PBXBuildFile; fileRef = 8FE3CCBB22DBF8D000B8EA87 /* UnusedDeclarationConfiguration.swift */; };
 		92CCB2D71E1EEFA300C8E5A3 /* UnusedOptionalBindingRule.swift in Sources */ = {isa = PBXBuildFile; fileRef = 92CCB2D61E1EEFA300C8E5A3 /* UnusedOptionalBindingRule.swift */; };
 		93E0C3CE1D67BD7F007FA25D /* ConditionalReturnsOnNewlineRule.swift in Sources */ = {isa = PBXBuildFile; fileRef = 93E0C3CD1D67BD7F007FA25D /* ConditionalReturnsOnNewlineRule.swift */; };
 		A1A6F3F21EE319ED00A9F9E2 /* ObjectLiteralConfiguration.swift in Sources */ = {isa = PBXBuildFile; fileRef = A1A6F3F11EE319ED00A9F9E2 /* ObjectLiteralConfiguration.swift */; };
@@ -506,6 +511,9 @@
 		1F11B3CE1C252F23002E8FA8 /* ClosingBraceRule.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = ClosingBraceRule.swift; sourceTree = "<group>"; };
 		24B4DF0B1D6DFA370097803B /* RedundantNilCoalescingRule.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = RedundantNilCoalescingRule.swift; sourceTree = "<group>"; };
 		24E17F701B1481FF008195BE /* File+Cache.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = "File+Cache.swift"; sourceTree = "<group>"; };
+		260F669F225C5B6D00407CF5 /* CollectingRuleTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = CollectingRuleTests.swift; sourceTree = "<group>"; };
+		264E080E2248BA2800ADC4C5 /* RuleStorage.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = RuleStorage.swift; sourceTree = "<group>"; };
+		26CE462C228532CD00264485 /* Array+SwiftLint.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; name = "Array+SwiftLint.swift"; path = "../../SwiftLintFramework/Extensions/Array+SwiftLint.swift"; sourceTree = "<group>"; };
 		287F8B62223083ED00BDC504 /* NSLocalizedStringRequireBundleRule.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = NSLocalizedStringRequireBundleRule.swift; sourceTree = "<group>"; };
 		2882895B22287C9C0037CF5F /* NSObjectPreferIsEqualRule.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = NSObjectPreferIsEqualRule.swift; sourceTree = "<group>"; };
 		2882895D22287E2C0037CF5F /* NSObjectPreferIsEqualRuleExamples.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = NSObjectPreferIsEqualRuleExamples.swift; sourceTree = "<group>"; };
@@ -644,6 +652,7 @@
 		856651A61D6B395F005E6B29 /* MarkRule.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = MarkRule.swift; sourceTree = "<group>"; };
 		8B01E4FB20A4183C00C9233E /* FunctionParameterCountConfiguration.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = FunctionParameterCountConfiguration.swift; sourceTree = "<group>"; };
 		8B01E4FF20A4340A00C9233E /* FunctionParameterCountRuleTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = FunctionParameterCountRuleTests.swift; sourceTree = "<group>"; };
+		8F0856EA22DA8508001FF4D4 /* UnusedDeclarationRule.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = UnusedDeclarationRule.swift; sourceTree = "<group>"; };
 		8F2CC1CA20A6A070006ED34F /* FileNameConfiguration.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = FileNameConfiguration.swift; sourceTree = "<group>"; };
 		8F2CC1CC20A6A189006ED34F /* FileNameRuleTests.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = FileNameRuleTests.swift; sourceTree = "<group>"; };
 		8F6AA75A211905B8009BA28A /* LintableFilesVisitor.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = LintableFilesVisitor.swift; sourceTree = "<group>"; };
@@ -656,6 +665,7 @@
 		8FD216CB205584AF008ED13F /* CharacterSet+SwiftLint.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = "CharacterSet+SwiftLint.swift"; sourceTree = "<group>"; };
 		8FDF482B2122476D00521605 /* AnalyzeCommand.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = AnalyzeCommand.swift; sourceTree = "<group>"; };
 		8FDF482D21234BFF00521605 /* LintOrAnalyzeCommand.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = LintOrAnalyzeCommand.swift; sourceTree = "<group>"; };
+		8FE3CCBB22DBF8D000B8EA87 /* UnusedDeclarationConfiguration.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = UnusedDeclarationConfiguration.swift; sourceTree = "<group>"; };
 		92CCB2D61E1EEFA300C8E5A3 /* UnusedOptionalBindingRule.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = UnusedOptionalBindingRule.swift; sourceTree = "<group>"; };
 		93E0C3CD1D67BD7F007FA25D /* ConditionalReturnsOnNewlineRule.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = ConditionalReturnsOnNewlineRule.swift; sourceTree = "<group>"; };
 		A1A6F3F11EE319ED00A9F9E2 /* ObjectLiteralConfiguration.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = ObjectLiteralConfiguration.swift; sourceTree = "<group>"; };
@@ -1017,6 +1027,7 @@
 				BF48D2D61CBCCA5F0080BDAE /* TrailingWhitespaceConfiguration.swift */,
 				82DB55FF21008F54001C62FF /* TypeContentsOrderConfiguration.swift */,
 				CE8178EB1EAC02CD0063186E /* UnusedOptionalBindingConfiguration.swift */,
+				8FE3CCBB22DBF8D000B8EA87 /* UnusedDeclarationConfiguration.swift */,
 				006204DA1E1E48F900FFFBE1 /* VerticalWhitespaceConfiguration.swift */,
 			);
 			path = RuleConfigurations;
@@ -1121,6 +1132,7 @@
 				7565E5F02262BA0900B0597C /* UnusedCaptureListRule.swift */,
 				D40AD0891E032F9700F48C30 /* UnusedClosureParameterRule.swift */,
 				D4D7320C21E15ED4001C07D9 /* UnusedControlFlowLabelRule.swift */,
+				8F0856EA22DA8508001FF4D4 /* UnusedDeclarationRule.swift */,
 				8F715B82213B528B00427BD9 /* UnusedImportRule.swift */,
 				D4BED5F72278AECC00D86BCE /* UnownedVariableCaptureRule.swift */,
 				8F6B3153213CDCD100858E44 /* UnusedPrivateDeclarationRule.swift */,
@@ -1422,9 +1434,11 @@
 			children = (
 				D4998DE61DF191380006E05D /* AttributesRuleTests.swift */,
 				D4EAB3A320E9948D0051C09A /* AutomaticRuleTests.generated.swift */,
+				260F669F225C5B6D00407CF5 /* CollectingRuleTests.swift */,
 				7578C915214173BE0080FEC9 /* CollectionAlignmentRuleTests.swift */,
 				D43B04651E071ED3004016AF /* ColonRuleTests.swift */,
 				E81ADD731ED6052F000CD451 /* CommandTests.swift */,
+				BCB68282216213130078E4C3 /* CompilerProtocolInitRuleTests.swift */,
 				820F451D21073D7200AA056A /* ConditionalReturnsOnNewlineRuleTests.swift */,
 				D0D1212219E878CC005E4BAA /* Configuration */,
 				C2B3C15F2106F78100088928 /* ConfigurationAliasesTests.swift */,
@@ -1435,12 +1449,12 @@
 				3BB47D861C51DE6E00AE6A10 /* CustomRulesTests.swift */,
 				67932E2C1E54AF4B00CB0629 /* CyclomaticComplexityConfigurationTests.swift */,
 				67EB4DFB1E4CD7F5004E9ACD /* CyclomaticComplexityRuleTests.swift */,
-				CCD8B87720559C4A00B75847 /* DisableAllTests.swift */,
 				D41985EC21FAD033003BE2B7 /* DeploymentTargetConfigurationTests.swift */,
 				D41985EE21FAD5E8003BE2B7 /* DeploymentTargetRuleTests.swift */,
+				CCD8B87720559C4A00B75847 /* DisableAllTests.swift */,
 				62AF35D71F30B183009B11EE /* DiscouragedDirectInitRuleTests.swift */,
-				D48B51221F4F5E4B0068AB98 /* DocumentationTests.swift */,
 				D414D6AB21D0B77F00960935 /* DiscouragedObjectLiteralRuleTests.swift */,
+				D48B51221F4F5E4B0068AB98 /* DocumentationTests.swift */,
 				125CE52E20425EFD001635E5 /* ExplicitTypeInterfaceConfigurationTests.swift */,
 				12E3D4DB2042729300B3E30E /* ExplicitTypeInterfaceRuleTests.swift */,
 				02FD8AEE1BFC18D60014BFFB /* ExtendedNSStringTests.swift */,
@@ -1481,9 +1495,9 @@
 				787CDE3A208F9C34005F3D2F /* SwitchCaseAlignmentRuleTests.swift */,
 				E81224991B04F85B001783D2 /* TestHelpers.swift */,
 				D4DB92241E628898005DE9C1 /* TodoRuleTests.swift */,
-				C9802F2E1E0C8AEE008AB27F /* TrailingCommaRuleTests.swift */,
 				D450D1E121F19B1E00E60010 /* TrailingClosureConfigurationTests.swift */,
 				D450D1DE21F19A9400E60010 /* TrailingClosureRuleTests.swift */,
+				C9802F2E1E0C8AEE008AB27F /* TrailingCommaRuleTests.swift */,
 				D4F5851320E99A720085C6D8 /* TrailingWhitespaceTests.swift */,
 				820F451B2107292500AA056A /* TypeContentsOrderRuleTests.swift */,
 				3B20CD0B1EB699C20069EF2E /* TypeNameRuleTests.swift */,
@@ -1493,7 +1507,6 @@
 				627C7A312004F9290053C79D /* XCTSpecificMatcherRuleTests.swift */,
 				3B30C4A01C3785B300E04027 /* YamlParserTests.swift */,
 				3B12C9C21C320A53000B423F /* YamlSwiftLintTests.swift */,
-				BCB68282216213130078E4C3 /* CompilerProtocolInitRuleTests.swift */,
 			);
 			name = SwiftLintFrameworkTests;
 			path = Tests/SwiftLintFrameworkTests;
@@ -1598,6 +1611,7 @@
 				D4C27BFD1E12D53F00DF713E /* Version.swift */,
 				E88DEA701B09847500A66CB0 /* ViolationSeverity.swift */,
 				3BD9CD3C1C37175B009A5D25 /* YamlParser.swift */,
+				264E080E2248BA2800ADC4C5 /* RuleStorage.swift */,
 			);
 			path = Models;
 			sourceTree = "<group>";
@@ -1635,6 +1649,7 @@
 		E8B0677F1C13E48100E9E13F /* Extensions */ = {
 			isa = PBXGroup;
 			children = (
+				26CE462C228532CD00264485 /* Array+SwiftLint.swift */,
 				E8B067801C13E49600E9E13F /* Configuration+CommandLine.swift */,
 				E86E2B2D1E17443B001E823C /* Reporter+CommandLine.swift */,
 			);
@@ -1951,6 +1966,7 @@
 				29FC197A21382C07006D208C /* DuplicateImportsRuleExamples.swift in Sources */,
 				83D71E281B131ECE000395DE /* RuleDescription.swift in Sources */,
 				D4470D571EB69225008A1B2E /* ImplicitReturnRule.swift in Sources */,
+				8FE3CCBC22DBF8D000B8EA87 /* UnusedDeclarationConfiguration.swift in Sources */,
 				3B12C9C51C322032000B423F /* MasterRuleList.swift in Sources */,
 				E812249C1B04FADC001783D2 /* Linter.swift in Sources */,
 				1F11B3CF1C252F23002E8FA8 /* ClosingBraceRule.swift in Sources */,
@@ -2125,6 +2141,8 @@
 				E88198421BEA929F00333A11 /* NestingRule.swift in Sources */,
 				D46A317F1F1CEDCD00AF914A /* UnneededParenthesesInClosureArgumentRule.swift in Sources */,
 				D4470D591EB6B4D1008A1B2E /* EmptyEnumArgumentsRule.swift in Sources */,
+				8F0856EB22DA8508001FF4D4 /* UnusedDeclarationRule.swift in Sources */,
+				264E080F2248BA2800ADC4C5 /* RuleStorage.swift in Sources */,
 				627BC48D1F9405160004A6C2 /* QuickDiscouragedFocusedTestRule.swift in Sources */,
 				3BB47D851C51D80000AE6A10 /* NSRegularExpression+SwiftLint.swift in Sources */,
 				E881985B1BEA974E00333A11 /* StatementPositionRule.swift in Sources */,
@@ -2284,6 +2302,7 @@
 				C9802F2F1E0C8AEE008AB27F /* TrailingCommaRuleTests.swift in Sources */,
 				3B63D46F1E1F09DF0057BE35 /* LineLengthRuleTests.swift in Sources */,
 				627C7A322004F9290053C79D /* XCTSpecificMatcherRuleTests.swift in Sources */,
+				260F66A0225C5B6D00407CF5 /* CollectingRuleTests.swift in Sources */,
 				3BCC04D41C502BAB006073C3 /* RuleConfigurationTests.swift in Sources */,
 				E809EDA31B8A73FB00399043 /* ConfigurationTests.swift in Sources */,
 				8F2CC1CD20A6A189006ED34F /* FileNameRuleTests.swift in Sources */,
@@ -2301,6 +2320,7 @@
 				E802ED001C56A56000A35AE1 /* Benchmark.swift in Sources */,
 				E83A0B351A5D382B0041A60A /* VersionCommand.swift in Sources */,
 				E81FB3E41C6D507B00DC988F /* CommonOptions.swift in Sources */,
+				26CE462D228532CD00264485 /* Array+SwiftLint.swift in Sources */,
 				E861519B1B0573B900C54AC0 /* LintCommand.swift in Sources */,
 				D0E7B65619E9C76900EDBA4D /* main.swift in Sources */,
 				83894F221B0C928A006214E1 /* RulesCommand.swift in Sources */,

SwiftLint.xcodeproj/xcshareddata/xcschemes/swiftlint.xcscheme

@@ -69,7 +69,8 @@
       selectedDebuggerIdentifier = "Xcode.DebuggerFoundation.Debugger.LLDB"
       selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
       launchStyle = "0"
-      useCustomWorkingDirectory = "NO"
+      useCustomWorkingDirectory = "YES"
+      customWorkingDirectory = "~/Projects/Lyft-iOS"
       ignoresPersistentStateOnLaunch = "NO"
       debugDocumentVersioning = "NO"
       debugXPCServices = "NO"
@@ -88,9 +89,13 @@
       </BuildableProductRunnable>
       <CommandLineArguments>
          <CommandLineArgument
-            argument = "lint --no-cache"
+            argument = "analyze --quiet --strict --compiler-log-path xcodebuild.log"
             isEnabled = "YES">
          </CommandLineArgument>
+         <CommandLineArgument
+            argument = "lint --no-cache"
+            isEnabled = "NO">
+         </CommandLineArgument>
       </CommandLineArguments>
       <EnvironmentVariables>
          <EnvironmentVariable

Tests/LinuxMain.swift

@@ -69,6 +69,15 @@ extension ClosureSpacingRuleTests {
     ]
 }
 
+extension CollectingRuleTests {
+    static var allTests: [(String, (CollectingRuleTests) -> () throws -> Void)] = [
+        ("testCollectsIntoStorage", testCollectsIntoStorage),
+        ("testCollectsAllFiles", testCollectsAllFiles),
+        ("testCollectsAnalyzerFiles", testCollectsAnalyzerFiles),
+        ("testCorrects", testCorrects)
+    ]
+}
+
 extension CollectionAlignmentRuleTests {
     static var allTests: [(String, (CollectionAlignmentRuleTests) -> () throws -> Void)] = [
         ("testWithDefaultConfiguration", testWithDefaultConfiguration),
@@ -1381,6 +1390,12 @@ extension UnusedControlFlowLabelRuleTests {
     ]
 }
 
+extension UnusedDeclarationRuleTests {
+    static var allTests: [(String, (UnusedDeclarationRuleTests) -> () throws -> Void)] = [
+        ("testWithDefaultConfiguration", testWithDefaultConfiguration)
+    ]
+}
+
 extension UnusedEnumeratedRuleTests {
     static var allTests: [(String, (UnusedEnumeratedRuleTests) -> () throws -> Void)] = [
         ("testWithDefaultConfiguration", testWithDefaultConfiguration)
@@ -1532,6 +1547,7 @@ XCTMain([
     testCase(ClosureEndIndentationRuleTests.allTests),
     testCase(ClosureParameterPositionRuleTests.allTests),
     testCase(ClosureSpacingRuleTests.allTests),
+    testCase(CollectingRuleTests.allTests),
     testCase(CollectionAlignmentRuleTests.allTests),
     testCase(ColonRuleTests.allTests),
     testCase(CommaRuleTests.allTests),
@@ -1700,6 +1716,7 @@ XCTMain([
     testCase(UnusedCaptureListRuleTests.allTests),
     testCase(UnusedClosureParameterRuleTests.allTests),
     testCase(UnusedControlFlowLabelRuleTests.allTests),
+    testCase(UnusedDeclarationRuleTests.allTests),
     testCase(UnusedEnumeratedRuleTests.allTests),
     testCase(UnusedImportRuleTests.allTests),
     testCase(UnusedOptionalBindingRuleTests.allTests),

Tests/SwiftLintFrameworkTests/AutomaticRuleTests.generated.swift

@@ -714,6 +714,12 @@ class UnusedControlFlowLabelRuleTests: XCTestCase {
     }
 }
 
+class UnusedDeclarationRuleTests: XCTestCase {
+    func testWithDefaultConfiguration() {
+        verifyRule(UnusedDeclarationRule.description)
+    }
+}
+
 class UnusedEnumeratedRuleTests: XCTestCase {
     func testWithDefaultConfiguration() {
         verifyRule(UnusedEnumeratedRule.description)

Tests/SwiftLintFrameworkTests/CollectingRuleTests.swift

@@ -0,0 +1,125 @@
+import SourceKittenFramework
+@testable import SwiftLintFramework
+import XCTest
+
+// swiftlint:disable nesting
+
+class CollectingRuleTests: XCTestCase {
+    func testCollectsIntoStorage() {
+        struct Spec: MockCollectingRule {
+            func collectInfo(for file: File) -> Int {
+                return 42
+            }
+            func validate(file: File, collectedInfo: [File: Int]) -> [StyleViolation] {
+                XCTAssertEqual(collectedInfo[file], 42)
+                return [StyleViolation(ruleDescription: Spec.description,
+                                       location: Location(file: file, byteOffset: 0))]
+            }
+        }
+
+        XCTAssertFalse(violations("", config: Spec.configuration!).isEmpty)
+    }
+
+    func testCollectsAllFiles() {
+        struct Spec: MockCollectingRule {
+            func collectInfo(for file: File) -> String {
+                return file.contents
+            }
+            func validate(file: File, collectedInfo: [File: String]) -> [StyleViolation] {
+                let values = collectedInfo.values
+                XCTAssertTrue(values.contains("foo"))
+                XCTAssertTrue(values.contains("bar"))
+                XCTAssertTrue(values.contains("baz"))
+                return [StyleViolation(ruleDescription: Spec.description,
+                                       location: Location(file: file, byteOffset: 0))]
+            }
+        }
+
+        let inputs = ["foo", "bar", "baz"]
+        XCTAssertEqual(inputs.violations(config: Spec.configuration!).count, inputs.count)
+    }
+
+    func testCollectsAnalyzerFiles() {
+        struct Spec: MockCollectingRule & AnalyzerRule {
+            func collectInfo(for file: File, compilerArguments: [String]) -> [String] {
+                return compilerArguments
+            }
+            func validate(file: File, collectedInfo: [File: [String]], compilerArguments: [String])
+                -> [StyleViolation] {
+                    XCTAssertEqual(collectedInfo[file], compilerArguments)
+                    return [StyleViolation(ruleDescription: Spec.description,
+                                           location: Location(file: file, byteOffset: 0))]
+            }
+        }
+
+        XCTAssertFalse(violations("", config: Spec.configuration!, requiresFileOnDisk: true).isEmpty)
+    }
+
+    func testCorrects() {
+        struct Spec: MockCollectingRule & CollectingCorrectableRule {
+            func collectInfo(for file: File) -> String {
+                return file.contents
+            }
+
+            func validate(file: File, collectedInfo: [File: String]) -> [StyleViolation] {
+                if collectedInfo[file] == "baz" {
+                    return [StyleViolation(ruleDescription: Spec.description,
+                                           location: Location(file: file, byteOffset: 2))]
+                } else {
+                    return []
+                }
+            }
+
+            func correct(file: File, collectedInfo: [File: String]) -> [Correction] {
+                if collectedInfo[file] == "baz" {
+                    return [Correction(ruleDescription: Spec.description,
+                                       location: Location(file: file, byteOffset: 2))]
+                } else {
+                    return []
+                }
+            }
+        }
+
+        struct AnalyzerSpec: MockCollectingRule & AnalyzerRule & CollectingCorrectableRule {
+            func collectInfo(for file: File, compilerArguments: [String]) -> String {
+                return file.contents
+            }
+
+            func validate(file: File, collectedInfo: [File: String], compilerArguments: [String])
+                -> [StyleViolation] {
+                    if collectedInfo[file] == "baz" {
+                        return [StyleViolation(ruleDescription: Spec.description,
+                                               location: Location(file: file, byteOffset: 2))]
+                    } else {
+                        return []
+                    }
+            }
+
+            func correct(file: File, collectedInfo: [File: String], compilerArguments: [String]) -> [Correction] {
+                if collectedInfo[file] == "baz" {
+                    return [Correction(ruleDescription: Spec.description,
+                                       location: Location(file: file, byteOffset: 2))]
+                } else {
+                    return []
+                }
+            }
+        }
+
+        let inputs = ["foo", "baz"]
+        XCTAssertEqual(inputs.corrections(config: Spec.configuration!).count, 1)
+        XCTAssertEqual(inputs.corrections(config: AnalyzerSpec.configuration!, requiresFileOnDisk: true).count, 1)
+    }
+}
+
+private protocol MockCollectingRule: CollectingRule {}
+extension MockCollectingRule {
+    var configurationDescription: String { return "N/A" }
+    static var description: RuleDescription {
+        return RuleDescription(identifier: "test_rule", name: "", description: "", kind: .lint)
+    }
+    static var configuration: Configuration? {
+        return Configuration(rulesMode: .whitelisted([description.identifier]), ruleList: RuleList(rules: self))
+    }
+
+    init(configuration: Any) throws { self.init() }
+}

Tests/SwiftLintFrameworkTests/FunctionParameterCountRuleTests.swift

@@ -7,10 +7,6 @@ private func funcWithParameters(_ parameters: String, violates: Bool = false) ->
     return "func \(marker)abc(\(parameters)) {}\n"
 }
 
-private func violatingFuncWithParameters(_ parameters: String) -> String {
-    return funcWithParameters(parameters, violates: true)
-}
-
 class FunctionParameterCountRuleTests: XCTestCase {
     func testWithDefaultConfiguration() {
         verifyRule(FunctionParameterCountRule.description)
@@ -48,10 +44,4 @@ class FunctionParameterCountRuleTests: XCTestCase {
 
         verifyRule(description, ruleConfiguration: ["ignores_default_parameters": false])
     }
-
-    private func violations(_ string: String) -> [StyleViolation] {
-        let config = makeConfig(nil, FunctionParameterCountRule.description.identifier)!
-
-        return SwiftLintFrameworkTests.violations(string, config: config)
-    }
 }

Tests/SwiftLintFrameworkTests/IntegrationTests.swift

@@ -18,8 +18,9 @@ class IntegrationTests: XCTestCase {
         let swiftFiles = config.lintableFiles(inPath: "", forceExclude: false)
         XCTAssert(swiftFiles.contains(where: { #file == $0.path }), "current file should be included")
 
+        let storage = RuleStorage()
         let violations = swiftFiles.parallelFlatMap {
-            Linter(file: $0, configuration: config).styleViolations
+            Linter(file: $0, configuration: config).collect(into: storage).styleViolations(using: storage)
         }
         violations.forEach { violation in
             violation.location.file!.withStaticString {
@@ -30,7 +31,10 @@ class IntegrationTests: XCTestCase {
 
     func testSwiftLintAutoCorrects() {
         let swiftFiles = config.lintableFiles(inPath: "", forceExclude: false)
-        let corrections = swiftFiles.parallelFlatMap { Linter(file: $0, configuration: config).correct() }
+        let storage = RuleStorage()
+        let corrections = swiftFiles.parallelFlatMap {
+            Linter(file: $0, configuration: config).collect(into: storage).correct(using: storage)
+        }
         for correction in corrections {
             correction.location.file!.withStaticString {
                 XCTFail(correction.ruleDescription.description,

Tests/SwiftLintFrameworkTests/SourceKitCrashTests.swift

@@ -65,7 +65,8 @@ class SourceKitCrashTests: XCTestCase {
             XCTFail("If this called, rule's SourceKitFreeRule is not properly configured")
         }
         let configuration = Configuration(rulesMode: .whitelisted(allRuleIdentifiers))!
-        _ = Linter(file: file, configuration: configuration).styleViolations
+        let storage = RuleStorage()
+        _ = Linter(file: file, configuration: configuration).collect(into: storage).styleViolations(using: storage)
         file.sourcekitdFailed = false
         file.assertHandler = nil
     }

Tests/SwiftLintFrameworkTests/TestHelpers.swift

@@ -33,17 +33,78 @@ func violations(_ string: String, config: Configuration = Configuration()!,
     let stringStrippingMarkers = string.replacingOccurrences(of: violationMarker, with: "")
     guard requiresFileOnDisk else {
         let file = File(contents: stringStrippingMarkers)
-        let linter = Linter(file: file, configuration: config)
-        return linter.styleViolations
+        let storage = RuleStorage()
+        let linter = Linter(file: file, configuration: config).collect(into: storage)
+        return linter.styleViolations(using: storage)
     }
 
     let file = File.temporary(withContents: stringStrippingMarkers)
-    let linter = Linter(file: file, configuration: config, compilerArguments: file.makeCompilerArguments())
-    return linter.styleViolations.map { violation in
-        let locationWithoutFile = Location(file: nil, line: violation.location.line,
-                                           character: violation.location.character)
-        return StyleViolation(ruleDescription: violation.ruleDescription, severity: violation.severity,
-                              location: locationWithoutFile, reason: violation.reason)
+    let storage = RuleStorage()
+    let collecter = Linter(file: file, configuration: config, compilerArguments: file.makeCompilerArguments())
+    let linter = collecter.collect(into: storage)
+    return linter.styleViolations(using: storage).withoutFiles()
+}
+
+extension Collection where Element == String {
+    func violations(config: Configuration = Configuration()!, requiresFileOnDisk: Bool = false)
+        -> [StyleViolation] {
+            let makeFile = requiresFileOnDisk ? File.temporary : File.init(contents:)
+            return map(makeFile).violations(config: config, requiresFileOnDisk: requiresFileOnDisk)
+    }
+
+    func corrections(config: Configuration = Configuration()!, requiresFileOnDisk: Bool = false) -> [Correction] {
+        let makeFile = requiresFileOnDisk ? File.temporary : File.init(contents:)
+        return map(makeFile).corrections(config: config, requiresFileOnDisk: requiresFileOnDisk)
+    }
+}
+
+extension Collection where Element: File {
+    func violations(config: Configuration = Configuration()!, requiresFileOnDisk: Bool = false)
+        -> [StyleViolation] {
+            let storage = RuleStorage()
+            let violations = map({ file in
+                Linter(file: file, configuration: config,
+                       compilerArguments: requiresFileOnDisk ? file.makeCompilerArguments() : [])
+            }).map({ linter in
+                linter.collect(into: storage)
+            }).flatMap({ linter in
+                linter.styleViolations(using: storage)
+            })
+            return requiresFileOnDisk ? violations.withoutFiles() : violations
+    }
+
+    func corrections(config: Configuration = Configuration()!, requiresFileOnDisk: Bool = false) -> [Correction] {
+        let storage = RuleStorage()
+        let corrections = map({ file in
+            Linter(file: file, configuration: config,
+                   compilerArguments: requiresFileOnDisk ? file.makeCompilerArguments() : [])
+        }).map({ linter in
+            linter.collect(into: storage)
+        }).flatMap({ linter in
+            linter.correct(using: storage)
+        })
+        return requiresFileOnDisk ? corrections.withoutFiles() : corrections
+    }
+}
+
+private extension Collection where Element == StyleViolation {
+    func withoutFiles() -> [StyleViolation] {
+        return map { violation in
+            let locationWithoutFile = Location(file: nil, line: violation.location.line,
+                                               character: violation.location.character)
+            return StyleViolation(ruleDescription: violation.ruleDescription, severity: violation.severity,
+                                  location: locationWithoutFile, reason: violation.reason)
+        }
+    }
+}
+
+private extension Collection where Element == Correction {
+    func withoutFiles() -> [Correction] {
+        return map { correction in
+            let locationWithoutFile = Location(file: nil, line: correction.location.line,
+                                               character: correction.location.character)
+            return Correction(ruleDescription: correction.ruleDescription, location: locationWithoutFile)
+        }
     }
 }
 
@@ -98,8 +159,10 @@ private extension Configuration {
         let expectedLocations = markerOffsets.map { Location(file: file, characterOffset: $0) }
         let includeCompilerArguments = self.rules.contains(where: { $0 is AnalyzerRule })
         let compilerArguments = includeCompilerArguments ? file.makeCompilerArguments() : []
-        let linter = Linter(file: file, configuration: self, compilerArguments: compilerArguments)
-        let corrections = linter.correct().sorted { $0.location < $1.location }
+        let storage = RuleStorage()
+        let collecter = Linter(file: file, configuration: self, compilerArguments: compilerArguments)
+        let linter = collecter.collect(into: storage)
+        let corrections = linter.correct(using: storage).sorted { $0.location < $1.location }
         if expectedLocations.isEmpty {
             XCTAssertEqual(corrections.count, before != expected ? 1 : 0)
         } else {

script/oss-check

@@ -154,7 +154,7 @@ def generate_reports(branch)
       command = '../builds/.build/release/swiftlint lint --no-cache --enable-all-rules --reporter xcode'
       File.open("../#{branch}_reports/#{repo}.txt", 'w') do |file|
         puts "\n#{command}" if @options[:verbose]
-        Open3.popen3(command) do |_, stdout, _, wait_thr|
+        Open3.popen2(command) do |_, stdout, wait_thr|
           while line = stdout.gets
             file.puts line
           end
@@ -170,7 +170,7 @@ def generate_reports(branch)
         print "..#{i}"
         start = Time.now
         puts command if @options[:verbose]
-        Open3.popen3(command) { |_, stdout, _, _| stdout.read }
+        Open3.popen2(command) { |_, stdout, _| stdout.read }
         durations << Time.now - start
       end
       puts ''