simplify RegexConfiguration.cacheDescription

by respecting the value of ignoreCache rather than always passing 'true'

CHANGELOG.md

@@ -11,12 +11,31 @@
   [Marcelo Fabri](https://github.com/marcelofabri)
   [#1387](https://github.com/realm/SwiftLint/issues/1453)
 
+* Add `modificationDate(forFileAtPath:)` function requirement to
+  `LintableFileManager` protocol.  
+  [Victor Pimentel](https://github.com/victorpimentel)
+
+* Replace `configurationHash` parameters in all `LinterCache` initializers
+  with `configurationDescription` parameters.  
+  [Victor Pimentel](https://github.com/victorpimentel)
+
+* Remove `fileHash` parameter from `LinterCache.cache(violations:forFile:)`
+  and `LinterCache.violations(forFile:)` functions.  
+  [Victor Pimentel](https://github.com/victorpimentel)
+
+* Remove `hash` attribute from `Configuration` struct.  
+  [Victor Pimentel](https://github.com/victorpimentel)
+
 * Rename `ConditionalReturnsOnNewline` struct to
   `ConditionalReturnsOnNewlineRule` to match rule naming conventions.  
   [JP Simard](https://github.com/jpsim)
 
 ##### Enhancements
 
+* Cache linter results for files unmodified since the previous linter run.  
+  [Victor Pimentel](https://github.com/victorpimentel)
+  [#1184](https://github.com/realm/SwiftLint/issues/1184)
+
 * Add opt-in configurations to `generic_type_name`, `identifier_name` and
   `type_name` rules to allow excluding non-alphanumeric characters and names 
   that start with uppercase.  

Source/SwiftLintFramework/Extensions/NSFileManager+SwiftLint.swift

@@ -10,6 +10,7 @@ import Foundation
 
 public protocol LintableFileManager {
     func filesToLint(inPath: String, rootDirectory: String?) -> [String]
+    func modificationDate(forFileAtPath: String) -> Date?
 }
 
 extension FileManager: LintableFileManager {
@@ -31,4 +32,8 @@ extension FileManager: LintableFileManager {
             return nil
         } ?? []
     }
+
+    public func modificationDate(forFileAtPath path: String) -> Date? {
+        return (try? attributesOfItem(atPath: path))?[.modificationDate] as? Date
+    }
 }

Source/SwiftLintFramework/Models/Configuration.swift

@@ -9,8 +9,6 @@
 import Foundation
 import SourceKittenFramework
 
-private let fileManager = FileManager.default
-
 private enum ConfigurationKey: String {
     case cachePath = "cache_path"
     case disabledRules = "disabled_rules"
@@ -34,9 +32,25 @@ public struct Configuration: Equatable {
     public let rules: [Rule]
     public var rootPath: String?              // the root path to search for nested configurations
     public var configurationPath: String?     // if successfully loaded from a path
-    public var hash: Int?
     public let cachePath: String?
 
+    public var cacheDescription: String {
+        let cacheRulesDescriptions: [String: Any] = rules.reduce([:]) { accu, element in
+            var accu = accu
+            accu[type(of: element).description.identifier] = element.cacheDescription
+            return accu
+        }
+        let dict: [String: Any] = [
+            "root": rootPath ?? FileManager.default.currentDirectoryPath,
+            "rules": cacheRulesDescriptions
+        ]
+        if let jsonData = try? JSONSerialization.data(withJSONObject: dict),
+          let jsonString = String(data: jsonData, encoding: .utf8) {
+              return jsonString
+        }
+        fatalError("Could not serialize configuration for cache")
+    }
+
     public init?(disabledRules: [String] = [],
                  optInRules: [String] = [],
                  enableAllRules: Bool = false,
@@ -176,7 +190,6 @@ public struct Configuration: Equatable {
             }
             self.init(dict: dict, enableAllRules: enableAllRules)!
             configurationPath = fullPath
-            hash = dict.description.hashValue
             self.rootPath = rootPath
             return
         } catch YamlParserError.yamlParsing(let message) {
@@ -192,7 +205,7 @@ public struct Configuration: Equatable {
                   optional: !CommandLine.arguments.contains("--config"), quiet: quiet, enableAllRules: enableAllRules)
     }
 
-    public func lintablePaths(inPath path: String, fileManager: LintableFileManager = fileManager) -> [String] {
+    public func lintablePaths(inPath path: String, fileManager: LintableFileManager = FileManager.default) -> [String] {
         // If path is a Swift file, skip filtering with excluded/included paths
         if path.bridge().isSwiftFile() && path.isFile {
             return [path]

Source/SwiftLintFramework/Models/Linter.swift

@@ -85,8 +85,7 @@ public struct Linter {
         }
 
         if let cache = cache, let path = file.path {
-            let hash = file.contents.hash
-            cache.cache(violations: violations, forFile: path, fileHash: hash)
+            cache.cache(violations: violations, forFile: path)
         }
 
         for (deprecatedIdentifier, identifier) in deprecatedToValidIdentifier {
@@ -99,11 +98,8 @@ public struct Linter {
 
     private func cachedStyleViolations(benchmark: Bool = false) -> ([StyleViolation], [(id: String, time: Double)])? {
         let start: Date! = benchmark ? Date() : nil
-        guard let cache = cache,
-            let file = file.path,
-            case let hash = self.file.contents.hash,
-            let cachedViolations = cache.violations(forFile: file, hash: hash) else {
-                return nil
+        guard let cache = cache, let file = file.path, let cachedViolations = cache.violations(forFile: file) else {
+            return nil
         }
 
         var ruleTimes = [(id: String, time: Double)]()

Source/SwiftLintFramework/Models/LinterCache.swift

@@ -18,25 +18,26 @@ public enum LinterCacheError: Error {
 public final class LinterCache {
     private var cache: [String: Any]
     private let lock = NSLock()
+    internal lazy var fileManager: LintableFileManager = FileManager.default
 
-    public init(currentVersion: Version = .current, configurationHash: Int? = nil) {
+    public init(currentVersion: Version = .current, configurationDescription: String? = nil) {
         cache = [
-            "version": currentVersion.value,
-            "files": [:]
+            Key.version.rawValue: currentVersion.value,
+            Key.files.rawValue: [:]
         ]
-        cache["configuration_hash"] = configurationHash
+        cache[Key.configuration.rawValue] = configurationDescription
     }
 
-    public init(cache: Any, currentVersion: Version = .current, configurationHash: Int? = nil) throws {
+    public init(cache: Any, currentVersion: Version = .current, configurationDescription: String? = nil) throws {
         guard let dictionary = cache as? [String: Any] else {
             throw LinterCacheError.invalidFormat
         }
 
-        guard let version = dictionary["version"] as? String, version == currentVersion.value else {
+        guard dictionary[Key.version.rawValue] as? String == currentVersion.value else {
             throw LinterCacheError.differentVersion
         }
 
-        if dictionary["configuration_hash"] as? Int != configurationHash {
+        guard dictionary[Key.configuration.rawValue] as? String == configurationDescription else {
             throw LinterCacheError.differentConfiguration
         }
 
@@ -44,32 +45,40 @@ public final class LinterCache {
     }
 
     public convenience init(contentsOf url: URL, currentVersion: Version = .current,
-                            configurationHash: Int? = nil) throws {
+                            configurationDescription: String? = nil) throws {
         let data = try Data(contentsOf: url)
         let json = try JSONSerialization.jsonObject(with: data, options: [])
         try self.init(cache: json, currentVersion: currentVersion,
-                      configurationHash: configurationHash)
+                      configurationDescription: configurationDescription)
     }
 
-    public func cache(violations: [StyleViolation], forFile file: String, fileHash: Int) {
+    public func cache(violations: [StyleViolation], forFile file: String) {
+        guard let lastModification = fileManager.modificationDate(forFileAtPath: file) else {
+            return
+        }
+
         lock.lock()
-        var filesCache = (cache["files"] as? [String: Any]) ?? [:]
+        var filesCache = (cache[Key.files.rawValue] as? [String: Any]) ?? [:]
         filesCache[file] = [
-            "violations": violations.map(dictionary(for:)),
-            "hash": fileHash
+            Key.violations.rawValue: violations.map(dictionary(for:)),
+            Key.lastModification.rawValue: lastModification.timeIntervalSinceReferenceDate
         ]
-        cache["files"] = filesCache
+        cache[Key.files.rawValue] = filesCache
         lock.unlock()
     }
 
-    public func violations(forFile file: String, hash: Int) -> [StyleViolation]? {
+    public func violations(forFile file: String) -> [StyleViolation]? {
+        guard let lastModification = fileManager.modificationDate(forFileAtPath: file) else {
+            return nil
+        }
+
         lock.lock()
 
-        guard let filesCache = cache["files"] as? [String: Any],
+        guard let filesCache = cache[Key.files.rawValue] as? [String: Any],
             let entry = filesCache[file] as? [String: Any],
-            let cacheHash = entry["hash"] as? Int,
-            cacheHash == hash,
-            let violations = entry["violations"] as? [[String: Any]] else {
+            let cacheLastModification = entry[Key.lastModification.rawValue] as? TimeInterval,
+            cacheLastModification == lastModification.timeIntervalSinceReferenceDate,
+            let violations = entry[Key.violations.rawValue] as? [[String: Any]] else {
                 lock.unlock()
                 return nil
         }
@@ -87,29 +96,46 @@ public final class LinterCache {
 
     private func dictionary(for violation: StyleViolation) -> [String: Any] {
         return [
-            "line": violation.location.line ?? NSNull() as Any,
-            "character": violation.location.character ?? NSNull() as Any,
-            "severity": violation.severity.rawValue,
-            "type": violation.ruleDescription.name,
-            "rule_id": violation.ruleDescription.identifier,
-            "reason": violation.reason
+            Key.line.rawValue: violation.location.line ?? NSNull() as Any,
+            Key.character.rawValue: violation.location.character ?? NSNull() as Any,
+            Key.severity.rawValue: violation.severity.rawValue,
+            Key.type.rawValue: violation.ruleDescription.name,
+            Key.ruleID.rawValue: violation.ruleDescription.identifier,
+            Key.reason.rawValue: violation.reason
         ]
     }
 }
 
+extension LinterCache {
+    fileprivate enum Key: String {
+        case character
+        case configuration
+        case files
+        case lastModification = "last_modification"
+        case line
+        case reason
+        case ruleID = "rule_id"
+        case severity
+        case type
+        case version
+        case violations
+    }
+}
+
 extension StyleViolation {
     fileprivate static func from(cache: [String: Any], file: String) -> StyleViolation? {
-        guard let severity = (cache["severity"] as? String).flatMap({ ViolationSeverity(rawValue: $0) }),
-            let name = cache["type"] as? String,
-            let ruleId = cache["rule_id"] as? String,
-            let reason = cache["reason"] as? String else {
+        guard let severityString = (cache[LinterCache.Key.severity.rawValue] as? String),
+            let severity = ViolationSeverity(rawValue: severityString),
+            let name = cache[LinterCache.Key.type.rawValue] as? String,
+            let ruleID = cache[LinterCache.Key.ruleID.rawValue] as? String,
+            let reason = cache[LinterCache.Key.reason.rawValue] as? String else {
                 return nil
         }
 
-        let line = cache["line"] as? Int
-        let character = cache["character"] as? Int
+        let line = cache[LinterCache.Key.line.rawValue] as? Int
+        let character = cache[LinterCache.Key.character.rawValue] as? Int
 
-        let ruleDescription = RuleDescription(identifier: ruleId, name: name, description: reason)
+        let ruleDescription = RuleDescription(identifier: ruleID, name: name, description: reason)
         let location = Location(file: file, line: line, character: character)
         let violation = StyleViolation(ruleDescription: ruleDescription, severity: severity,
                                        location: location, reason: reason)

Source/SwiftLintFramework/Protocols/CacheDescriptionProvider.swift

@@ -0,0 +1,11 @@
+//
+//  CacheDescriptionProvider.swift
+//  SwiftLint
+//
+//  Created by JP Simard on 5/16/17.
+//  Copyright © 2017 Realm. All rights reserved.
+//
+
+internal protocol CacheDescriptionProvider {
+    var cacheDescription: String { get }
+}

Source/SwiftLintFramework/Protocols/Rule.swift

@@ -21,6 +21,10 @@ extension Rule {
     public func isEqualTo(_ rule: Rule) -> Bool {
         return type(of: self).description == type(of: rule).description
     }
+
+    internal var cacheDescription: String {
+        return (self as? CacheDescriptionProvider)?.cacheDescription ?? configurationDescription
+    }
 }
 
 public protocol OptInRule: Rule {}

Source/SwiftLintFramework/Protocols/RuleConfiguration.swift

@@ -6,14 +6,18 @@
 //  Copyright © 2016 Realm. All rights reserved.
 //
 
-import Foundation
-
 public protocol RuleConfiguration {
     mutating func apply(configuration: Any) throws
     func isEqualTo(_ ruleConfiguration: RuleConfiguration) -> Bool
     var consoleDescription: String { get }
 }
 
+extension RuleConfiguration {
+    internal var cacheDescription: String {
+        return (self as? CacheDescriptionProvider)?.cacheDescription ?? consoleDescription
+    }
+}
+
 extension RuleConfiguration where Self: Equatable {
     public func isEqualTo(_ ruleConfiguration: RuleConfiguration) -> Bool {
         return self == ruleConfiguration as? Self

Source/SwiftLintFramework/Rules/CustomRules.swift

@@ -17,8 +17,11 @@ private extension Region {
 
 // MARK: - CustomRulesConfiguration
 
-public struct CustomRulesConfiguration: RuleConfiguration, Equatable {
+public struct CustomRulesConfiguration: RuleConfiguration, Equatable, CacheDescriptionProvider {
     public var consoleDescription: String { return "user-defined" }
+    internal var cacheDescription: String {
+        return customRuleConfigurations.map({ $0.cacheDescription }).joined(separator: "\n")
+    }
     public var customRuleConfigurations = [RegexConfiguration]()
 
     public init() {}
@@ -42,7 +45,11 @@ public func == (lhs: CustomRulesConfiguration, rhs: CustomRulesConfiguration) ->
 
 // MARK: - CustomRules
 
-public struct CustomRules: Rule, ConfigurationProviderRule {
+public struct CustomRules: Rule, ConfigurationProviderRule, CacheDescriptionProvider {
+
+    internal var cacheDescription: String {
+        return configuration.cacheDescription
+    }
 
     public static let description = RuleDescription(
         identifier: "custom_rules",

Source/SwiftLintFramework/Rules/RuleConfigurations/RegexConfiguration.swift

@@ -9,7 +9,7 @@
 import Foundation
 import SourceKittenFramework
 
-public struct RegexConfiguration: RuleConfiguration, Equatable {
+public struct RegexConfiguration: RuleConfiguration, Equatable, CacheDescriptionProvider {
     public let identifier: String
     public var name: String?
     public var message = "Regex matched."
@@ -27,6 +27,23 @@ public struct RegexConfiguration: RuleConfiguration, Equatable {
         return "\(severity.rawValue): \(regex.pattern)"
     }
 
+    internal var cacheDescription: String {
+        var dict = [String: Any]()
+        dict["identifier"] = identifier
+        dict["name"] = name
+        dict["message"] = message
+        dict["regex"] = regex.pattern
+        dict["included"] = included?.pattern
+        dict["excluded"] = excluded?.pattern
+        dict["match_kinds"] = matchKinds.map { $0.rawValue }
+        dict["severity"] = severityConfiguration.consoleDescription
+        if let jsonData = try? JSONSerialization.data(withJSONObject: dict),
+          let jsonString = String(data: jsonData, encoding: .utf8) {
+              return jsonString
+        }
+        fatalError("Could not serialize regex configuration for cache")
+    }
+
     public var description: RuleDescription {
         return RuleDescription(identifier: identifier, name: name ?? identifier, description: "")
     }

Source/swiftlint/Commands/LintCommand.swift

@@ -140,7 +140,7 @@ struct LintOptions: OptionsProtocol {
     // swiftlint:disable line_length
     static func create(_ path: String) -> (_ useSTDIN: Bool) -> (_ configurationFile: String) -> (_ strict: Bool) -> (_ lenient: Bool) -> (_ useScriptInputFiles: Bool) -> (_ benchmark: Bool) -> (_ reporter: String) -> (_ quiet: Bool) -> (_ cachePath: String) -> (_ ignoreCache: Bool) -> (_ enableAllRules: Bool) -> LintOptions {
         return { useSTDIN in { configurationFile in { strict in { lenient in { useScriptInputFiles in { benchmark in { reporter in { quiet in { cachePath in { ignoreCache in { enableAllRules in
-            self.init(path: path, useSTDIN: useSTDIN, configurationFile: configurationFile, strict: strict, lenient: lenient, useScriptInputFiles: useScriptInputFiles, benchmark: benchmark, reporter: reporter, quiet: quiet, cachePath: cachePath, ignoreCache: true, enableAllRules: enableAllRules)
+            self.init(path: path, useSTDIN: useSTDIN, configurationFile: configurationFile, strict: strict, lenient: lenient, useScriptInputFiles: useScriptInputFiles, benchmark: benchmark, reporter: reporter, quiet: quiet, cachePath: cachePath, ignoreCache: ignoreCache, enableAllRules: enableAllRules)
         }}}}}}}}}}}
     }
 

Source/swiftlint/Extensions/LinterCache+CommandLine.swift

@@ -16,12 +16,12 @@ extension LinterCache {
             return nil
         }
 
-        let configurationHash = configuration.hash
+        let configurationDescription = configuration.cacheDescription
         let cache: LinterCache
         do {
-            cache = try LinterCache(contentsOf: url, configurationHash: configurationHash)
+            cache = try LinterCache(contentsOf: url, configurationDescription: configurationDescription)
         } catch {
-            cache = LinterCache(configurationHash: configurationHash)
+            cache = LinterCache(configurationDescription: configurationDescription)
         }
 
         return cache
@@ -50,7 +50,7 @@ private func defaultCacheURL(options: LintOptions) -> URL {
     #if os(Linux)
         let baseURL = URL(fileURLWithPath: "/var/tmp/")
     #else
-        let baseURL = FileManager.default.urls(for: .applicationSupportDirectory, in: .userDomainMask)[0]
+        let baseURL = FileManager.default.urls(for: .cachesDirectory, in: .userDomainMask)[0]
     #endif
 
     let fileName = String(rootPath.hash) + ".json"

SwiftLint.xcodeproj/project.pbxproj

@@ -120,8 +120,8 @@
 		D44254201DB87CA200492EA4 /* ValidIBInspectableRule.swift in Sources */ = {isa = PBXBuildFile; fileRef = D442541E1DB87C3D00492EA4 /* ValidIBInspectableRule.swift */; };
 		D44254271DB9C15C00492EA4 /* SyntacticSugarRule.swift in Sources */ = {isa = PBXBuildFile; fileRef = D44254251DB9C12300492EA4 /* SyntacticSugarRule.swift */; };
 		D4470D571EB69225008A1B2E /* ImplicitReturnRule.swift in Sources */ = {isa = PBXBuildFile; fileRef = D4470D561EB69225008A1B2E /* ImplicitReturnRule.swift */; };
-		D4470D5B1EB76F44008A1B2E /* UnusedOptionalBindingRuleTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = D4470D5A1EB76F44008A1B2E /* UnusedOptionalBindingRuleTests.swift */; };
 		D4470D591EB6B4D1008A1B2E /* EmptyEnumArgumentsRule.swift in Sources */ = {isa = PBXBuildFile; fileRef = D4470D581EB6B4D1008A1B2E /* EmptyEnumArgumentsRule.swift */; };
+		D4470D5B1EB76F44008A1B2E /* UnusedOptionalBindingRuleTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = D4470D5A1EB76F44008A1B2E /* UnusedOptionalBindingRuleTests.swift */; };
 		D44AD2761C0AA5350048F7B0 /* LegacyConstructorRule.swift in Sources */ = {isa = PBXBuildFile; fileRef = D44AD2741C0AA3730048F7B0 /* LegacyConstructorRule.swift */; };
 		D462021F1E15F52D0027AAD1 /* NumberSeparatorRuleExamples.swift in Sources */ = {isa = PBXBuildFile; fileRef = D462021E1E15F52D0027AAD1 /* NumberSeparatorRuleExamples.swift */; };
 		D46252541DF63FB200BE2CA1 /* NumberSeparatorRule.swift in Sources */ = {isa = PBXBuildFile; fileRef = D46252531DF63FB200BE2CA1 /* NumberSeparatorRule.swift */; };
@@ -170,6 +170,7 @@
 		E315B83C1DFA4BC500621B44 /* DynamicInlineRule.swift in Sources */ = {isa = PBXBuildFile; fileRef = E315B83B1DFA4BC500621B44 /* DynamicInlineRule.swift */; };
 		E57B23C11B1D8BF000DEA512 /* ReturnArrowWhitespaceRule.swift in Sources */ = {isa = PBXBuildFile; fileRef = E57B23C01B1D8BF000DEA512 /* ReturnArrowWhitespaceRule.swift */; };
 		E802ED001C56A56000A35AE1 /* Benchmark.swift in Sources */ = {isa = PBXBuildFile; fileRef = E802ECFF1C56A56000A35AE1 /* Benchmark.swift */; };
+		E80746F61ECB722F00548D31 /* CacheDescriptionProvider.swift in Sources */ = {isa = PBXBuildFile; fileRef = E80746F51ECB722F00548D31 /* CacheDescriptionProvider.swift */; };
 		E809EDA11B8A71DF00399043 /* Configuration.swift in Sources */ = {isa = PBXBuildFile; fileRef = E809EDA01B8A71DF00399043 /* Configuration.swift */; };
 		E809EDA31B8A73FB00399043 /* ConfigurationTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = E809EDA21B8A73FB00399043 /* ConfigurationTests.swift */; };
 		E80E018D1B92C0F60078EB70 /* Command.swift in Sources */ = {isa = PBXBuildFile; fileRef = E80E018C1B92C0F60078EB70 /* Command.swift */; };
@@ -409,8 +410,8 @@
 		D442541E1DB87C3D00492EA4 /* ValidIBInspectableRule.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = ValidIBInspectableRule.swift; sourceTree = "<group>"; };
 		D44254251DB9C12300492EA4 /* SyntacticSugarRule.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = SyntacticSugarRule.swift; sourceTree = "<group>"; };
 		D4470D561EB69225008A1B2E /* ImplicitReturnRule.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = ImplicitReturnRule.swift; sourceTree = "<group>"; };
-		D4470D5A1EB76F44008A1B2E /* UnusedOptionalBindingRuleTests.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = UnusedOptionalBindingRuleTests.swift; sourceTree = "<group>"; };
 		D4470D581EB6B4D1008A1B2E /* EmptyEnumArgumentsRule.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = EmptyEnumArgumentsRule.swift; sourceTree = "<group>"; };
+		D4470D5A1EB76F44008A1B2E /* UnusedOptionalBindingRuleTests.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = UnusedOptionalBindingRuleTests.swift; sourceTree = "<group>"; };
 		D44AD2741C0AA3730048F7B0 /* LegacyConstructorRule.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = LegacyConstructorRule.swift; sourceTree = "<group>"; };
 		D462021E1E15F52D0027AAD1 /* NumberSeparatorRuleExamples.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = NumberSeparatorRuleExamples.swift; sourceTree = "<group>"; };
 		D46252531DF63FB200BE2CA1 /* NumberSeparatorRule.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = NumberSeparatorRule.swift; sourceTree = "<group>"; };
@@ -460,6 +461,7 @@
 		E57B23C01B1D8BF000DEA512 /* ReturnArrowWhitespaceRule.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = ReturnArrowWhitespaceRule.swift; sourceTree = "<group>"; };
 		E5A167C81B25A0B000CF2D03 /* OperatorFunctionWhitespaceRule.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = OperatorFunctionWhitespaceRule.swift; sourceTree = "<group>"; };
 		E802ECFF1C56A56000A35AE1 /* Benchmark.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = Benchmark.swift; sourceTree = "<group>"; };
+		E80746F51ECB722F00548D31 /* CacheDescriptionProvider.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = CacheDescriptionProvider.swift; sourceTree = "<group>"; };
 		E809EDA01B8A71DF00399043 /* Configuration.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = Configuration.swift; sourceTree = "<group>"; };
 		E809EDA21B8A73FB00399043 /* ConfigurationTests.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = ConfigurationTests.swift; sourceTree = "<group>"; };
 		E80E018C1B92C0F60078EB70 /* Command.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = Command.swift; sourceTree = "<group>"; };
@@ -935,6 +937,7 @@
 			isa = PBXGroup;
 			children = (
 				E88DEA8B1B0999A000A66CB0 /* ASTRule.swift */,
+				E80746F51ECB722F00548D31 /* CacheDescriptionProvider.swift */,
 				E86396C11BADAAE5002C9E88 /* Reporter.swift */,
 				E88DEA761B098D0C00A66CB0 /* Rule.swift */,
 				3B828E521C546468000D180E /* RuleConfiguration.swift */,
@@ -1330,6 +1333,7 @@
 				F22314B01D4FA4D7009AD165 /* LegacyNSGeometryFunctionsRule.swift in Sources */,
 				E88DEA8C1B0999A000A66CB0 /* ASTRule.swift in Sources */,
 				1E82D5591D7775C7009553D7 /* ClosureSpacingRule.swift in Sources */,
+				E80746F61ECB722F00548D31 /* CacheDescriptionProvider.swift in Sources */,
 				094385041D5D4F7C009168CF /* PrivateOutletRule.swift in Sources */,
 				E88DEA6B1B0983FE00A66CB0 /* StyleViolation.swift in Sources */,
 				3BB47D831C514E8100AE6A10 /* RegexConfiguration.swift in Sources */,

Tests/SwiftLintFrameworkTests/ConfigurationTests.swift

@@ -131,6 +131,10 @@ class ConfigurationTests: XCTestCase {
             XCTFail("Should not be called with path \(path)")
             return []
         }
+
+        public func modificationDate(forFileAtPath path: String) -> Date? {
+            return nil
+        }
     }
 
     func testExcludedPaths() {

Tests/SwiftLintFrameworkTests/LinterCacheTests.swift

@@ -12,6 +12,20 @@ import XCTest
 
 class LinterCacheTests: XCTestCase {
 
+    private class TestFileManager: LintableFileManager {
+        func filesToLint(inPath: String, rootDirectory: String? = nil) -> [String] {
+            return []
+        }
+
+        internal var stubbedModificationDateByPath: [String: Date] = [:]
+
+        public func modificationDate(forFileAtPath path: String) -> Date? {
+            return stubbedModificationDateByPath[path]
+        }
+    }
+
+    private let fileManager = TestFileManager()
+
     func testInitThrowsWhenUsingDifferentVersion() {
         let cache = ["version": "0.1.0"]
         checkError(LinterCacheError.differentVersion) {
@@ -27,10 +41,10 @@ class LinterCacheTests: XCTestCase {
     }
 
     func testInitThrowsWhenUsingDifferentConfiguration() {
-        let cache = ["version": "0.1.0", "configuration_hash": 1] as [String : Any]
+        let cache = ["version": "0.1.0", "configuration": "Configuration 1"] as [String : Any]
         checkError(LinterCacheError.differentConfiguration) {
             _ = try LinterCache(cache: cache, currentVersion: Version(value: "0.1.0"),
-                                configurationHash: 2)
+                                configurationDescription: "Configuration 2")
         }
     }
 
@@ -40,15 +54,16 @@ class LinterCacheTests: XCTestCase {
         XCTAssertNotNil(linterCache)
     }
 
-    func testInitSucceedsWithConfigurationHash() {
-        let cache = ["version": "0.2.0", "configuration_hash": 1] as [String : Any]
+    func testInitSucceedsWithConfiguration() {
+        let cache = ["version": "0.2.0", "configuration": "Configuration 1"] as [String : Any]
         let linterCache = try? LinterCache(cache: cache, currentVersion: Version(value: "0.2.0"),
-                                           configurationHash: 1)
+                                           configurationDescription: "Configuration 1")
         XCTAssertNotNil(linterCache)
     }
 
     func testParsesViolations() {
         let cache = LinterCache(currentVersion: Version(value: "0.2.0"))
+        cache.fileManager = fileManager
         let file = "foo.swift"
         let ruleDescription = RuleDescription(identifier: "rule", name: "Some rule",
                                               description: "Validates stuff")
@@ -62,27 +77,72 @@ class LinterCacheTests: XCTestCase {
                            location: Location(file: file, line: 5, character: nil),
                            reason: "Something is wrong.")
         ]
+        fileManager.stubbedModificationDateByPath[file] = Date()
 
-        cache.cache(violations: violations, forFile: file, fileHash: 1)
-        let cachedViolations = cache.violations(forFile: file, hash: 1)
+        cache.cache(violations: violations, forFile: file)
+        let cachedViolations = cache.violations(forFile: file)
 
         XCTAssertNotNil(cachedViolations)
         XCTAssertEqual(cachedViolations!, violations)
     }
 
-    func testParsesViolationsWithModifiedHash() {
+    func testParsesViolationsWithEmptyViolations() {
         let cache = LinterCache(currentVersion: Version(value: "0.2.0"))
+        cache.fileManager = fileManager
         let file = "foo.swift"
-        cache.cache(violations: [], forFile: file, fileHash: 1)
-        let cachedViolations = cache.violations(forFile: file, hash: 2)
+        fileManager.stubbedModificationDateByPath[file] = Date()
+
+        let cachedViolations = cache.violations(forFile: file)
 
         XCTAssertNil(cachedViolations)
     }
 
-    func testParsesViolationsWithEmptyViolations() {
+    func testParsesViolationsWithNoDate() {
         let cache = LinterCache(currentVersion: Version(value: "0.2.0"))
+        cache.fileManager = fileManager
         let file = "foo.swift"
-        let cachedViolations = cache.violations(forFile: file, hash: 2)
+        let ruleDescription = RuleDescription(identifier: "rule", name: "Some rule",
+                                              description: "Validates stuff")
+        let violations = [
+            StyleViolation(ruleDescription: ruleDescription,
+                           severity: .warning,
+                           location: Location(file: file, line: 10, character: 2),
+                           reason: "Something is not right."),
+            StyleViolation(ruleDescription: ruleDescription,
+                           severity: .error,
+                           location: Location(file: file, line: 5, character: nil),
+                           reason: "Something is wrong.")
+        ]
+        fileManager.stubbedModificationDateByPath[file] = Date()
+
+        cache.cache(violations: violations, forFile: file)
+        fileManager.stubbedModificationDateByPath[file] = nil
+        let cachedViolations = cache.violations(forFile: file)
+
+        XCTAssertNil(cachedViolations)
+    }
+
+    func testParsesViolationsWithDifferentDate() {
+        let cache = LinterCache(currentVersion: Version(value: "0.2.0"))
+        cache.fileManager = fileManager
+        let file = "foo.swift"
+        let ruleDescription = RuleDescription(identifier: "rule", name: "Some rule",
+                                              description: "Validates stuff")
+        let violations = [
+            StyleViolation(ruleDescription: ruleDescription,
+                           severity: .warning,
+                           location: Location(file: file, line: 10, character: 2),
+                           reason: "Something is not right."),
+            StyleViolation(ruleDescription: ruleDescription,
+                           severity: .error,
+                           location: Location(file: file, line: 5, character: nil),
+                           reason: "Something is wrong.")
+        ]
+        fileManager.stubbedModificationDateByPath[file] = Date()
+
+        cache.cache(violations: violations, forFile: file)
+        fileManager.stubbedModificationDateByPath[file] = Date()
+        let cachedViolations = cache.violations(forFile: file)
 
         XCTAssertNil(cachedViolations)
     }
@@ -95,10 +155,11 @@ extension LinterCacheTests {
             ("testInitThrowsWhenUsingInvalidCacheFormat", testInitThrowsWhenUsingInvalidCacheFormat),
             ("testInitThrowsWhenUsingDifferentConfiguration", testInitThrowsWhenUsingDifferentConfiguration),
             ("testInitSucceeds", testInitSucceeds),
-            ("testInitSucceedsWithConfigurationHash", testInitSucceedsWithConfigurationHash),
+            ("testInitSucceedsWithConfiguration", testInitSucceedsWithConfiguration),
             ("testParsesViolations", testParsesViolations),
-            ("testParsesViolationsWithModifiedHash", testParsesViolationsWithModifiedHash),
-            ("testParsesViolationsWithEmptyViolations", testParsesViolationsWithEmptyViolations)
+            ("testParsesViolationsWithEmptyViolations", testParsesViolationsWithEmptyViolations),
+            ("testParsesViolationsWithNoDate", testParsesViolationsWithNoDate),
+            ("testParsesViolationsWithDifferentDate", testParsesViolationsWithDifferentDate)
         ]
     }
 }