Add discarded_notification_center_observer rule

CHANGELOG.md

@@ -10,6 +10,13 @@
   `redundant_nil_coalescing` rules.  
   [Marcelo Fabri](https://github.com/marcelofabri)
 
+* Add `discarded_notification_center_observer` rule
+  that warns when the result of
+  `NotificationCenter.addObserver(forName:object:queue:using:)`
+  is not stored so it can be removed later.  
+  [Marcelo Fabri](https://github.com/marcelofabri)
+  [#1062](https://github.com/realm/SwiftLint/issues/1062)
+
 ##### Bug Fixes
 
 * None.

Source/SwiftLintFramework/Models/MasterRuleList.swift

@@ -83,6 +83,7 @@ public let masterRuleList = RuleList(rules:
     ControlStatementRule.self,
     CustomRules.self,
     CyclomaticComplexityRule.self,
+    DiscardedNotificationCenterObserverRule.self,
     DynamicInlineRule.self,
     EmptyCountRule.self,
     EmptyParametersRule.self,

Source/SwiftLintFramework/Rules/DiscardedNotificationCenterObserverRule.swift

@@ -0,0 +1,62 @@
+//
+//  DiscardedNotificationCenterObserverRule.swift
+//  SwiftLint
+//
+//  Created by Marcelo Fabri on 01/13/17.
+//  Copyright © 2017 Realm. All rights reserved.
+//
+
+import Foundation
+import SourceKittenFramework
+
+public struct DiscardedNotificationCenterObserverRule: ASTRule, ConfigurationProviderRule {
+    public var configuration = SeverityConfiguration(.warning)
+
+    public init() {}
+
+    public static let description = RuleDescription(
+        identifier: "discarded_notification_center_observer",
+        name: "Discarded Notification Center Observer",
+        description: "When registing for a notification using a block, the opaque observer that is " +
+                     "returned should be stored so it can be removed later.",
+        nonTriggeringExamples: [
+            "let foo = nc.addObserver(forName: .NSSystemTimeZoneDidChange, object: nil, queue: nil) { }\n",
+            "let foo = nc.addObserver(forName: .NSSystemTimeZoneDidChange, object: nil, queue: nil, using: { })\n"
+        ],
+        triggeringExamples: [
+            "↓nc.addObserver(forName: .NSSystemTimeZoneDidChange, object: nil, queue: nil) { }\n",
+            "↓nc.addObserver(forName: .NSSystemTimeZoneDidChange, object: nil, queue: nil, using: { })\n"
+        ]
+    )
+
+    public func validate(file: File, kind: SwiftExpressionKind,
+                         dictionary: [String: SourceKitRepresentable]) -> [StyleViolation] {
+        return violationOffsets(in: file, dictionary: dictionary, kind: kind).map { location in
+            StyleViolation(ruleDescription: type(of: self).description,
+                           severity: configuration.severity,
+                           location: Location(file: file, byteOffset: location))
+        }
+    }
+
+    private func violationOffsets(in file: File, dictionary: [String: SourceKitRepresentable],
+                                  kind: SwiftExpressionKind) -> [Int] {
+        guard kind == .call,
+            let name = dictionary.name,
+            name.hasSuffix(".addObserver"),
+            case let arguments = dictionary.enclosedArguments,
+            case let argumentsNames = arguments.flatMap({ $0.name }),
+            argumentsNames == ["forName", "object", "queue"] ||
+                argumentsNames == ["forName", "object", "queue", "using"],
+            let offset = dictionary.offset,
+            let range = file.contents.bridge().byteRangeToNSRange(start: 0, length: offset) else {
+                return []
+        }
+
+        if let lastMatch = regex("\\s?=\\s*").matches(in: file.contents, options: [], range: range).last?.range,
+            lastMatch.location == range.length - lastMatch.length {
+            return []
+        }
+
+        return [offset]
+    }
+}

SwiftLint.xcodeproj/project.pbxproj

@@ -139,6 +139,7 @@
 		D4DA1DF81E175E8A0037413D /* LinterCache+CommandLine.swift in Sources */ = {isa = PBXBuildFile; fileRef = D4DA1DF71E175E8A0037413D /* LinterCache+CommandLine.swift */; };
 		D4DA1DFA1E18D6200037413D /* LargeTupleRule.swift in Sources */ = {isa = PBXBuildFile; fileRef = D4DA1DF91E18D6200037413D /* LargeTupleRule.swift */; };
 		D4DA1DFE1E1A10DB0037413D /* NumberSeparatorConfiguration.swift in Sources */ = {isa = PBXBuildFile; fileRef = D4DA1DFD1E1A10DB0037413D /* NumberSeparatorConfiguration.swift */; };
+		D4DABFD31E29B4A5009617B6 /* DiscardedNotificationCenterObserverRule.swift in Sources */ = {isa = PBXBuildFile; fileRef = D4DABFD21E29B4A5009617B6 /* DiscardedNotificationCenterObserverRule.swift */; };
 		D4DAE8BC1DE14E8F00B0AE7A /* NimbleOperatorRule.swift in Sources */ = {isa = PBXBuildFile; fileRef = D4DAE8BB1DE14E8F00B0AE7A /* NimbleOperatorRule.swift */; };
 		D4FBADD01E00DA0400669C73 /* OperatorUsageWhitespaceRule.swift in Sources */ = {isa = PBXBuildFile; fileRef = D4FBADCF1E00DA0400669C73 /* OperatorUsageWhitespaceRule.swift */; };
 		D4FD58B21E12A0200019503C /* LinterCache.swift in Sources */ = {isa = PBXBuildFile; fileRef = D4FD58B11E12A0200019503C /* LinterCache.swift */; };
@@ -407,6 +408,7 @@
 		D4DA1DF71E175E8A0037413D /* LinterCache+CommandLine.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = "LinterCache+CommandLine.swift"; sourceTree = "<group>"; };
 		D4DA1DF91E18D6200037413D /* LargeTupleRule.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = LargeTupleRule.swift; sourceTree = "<group>"; };
 		D4DA1DFD1E1A10DB0037413D /* NumberSeparatorConfiguration.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = NumberSeparatorConfiguration.swift; sourceTree = "<group>"; };
+		D4DABFD21E29B4A5009617B6 /* DiscardedNotificationCenterObserverRule.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = DiscardedNotificationCenterObserverRule.swift; sourceTree = "<group>"; };
 		D4DAE8BB1DE14E8F00B0AE7A /* NimbleOperatorRule.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = NimbleOperatorRule.swift; sourceTree = "<group>"; };
 		D4FBADCF1E00DA0400669C73 /* OperatorUsageWhitespaceRule.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = OperatorUsageWhitespaceRule.swift; sourceTree = "<group>"; };
 		D4FD58B11E12A0200019503C /* LinterCache.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = LinterCache.swift; sourceTree = "<group>"; };
@@ -792,6 +794,7 @@
 				E88DEA831B0990F500A66CB0 /* ColonRule.swift */,
 				695BE9CE1BDFD92B0071E985 /* CommaRule.swift */,
 				D4DA1DF31E17511D0037413D /* CompilerProtocolInitRule.swift */,
+				D4DABFD21E29B4A5009617B6 /* DiscardedNotificationCenterObserverRule.swift */,
 				7C0C2E791D2866CB0076435A /* ExplicitInitRule.swift */,
 				93E0C3CD1D67BD7F007FA25D /* ConditionalReturnsOnNewline.swift */,
 				65454F451B14D73800319A6C /* ControlStatementRule.swift */,
@@ -1221,6 +1224,7 @@
 				D44254201DB87CA200492EA4 /* ValidIBInspectableRule.swift in Sources */,
 				85DA81321D6B471000951BC4 /* MarkRule.swift in Sources */,
 				D4A893351E15824100BF954D /* SwiftVersion.swift in Sources */,
+				D4DABFD31E29B4A5009617B6 /* DiscardedNotificationCenterObserverRule.swift in Sources */,
 				D4B022B21E10B613007E5297 /* RedundantVoidReturnRule.swift in Sources */,
 				3BCC04D21C4F56D3006073C3 /* NameConfiguration.swift in Sources */,
 				D4C27BFE1E12D53F00DF713E /* Version.swift in Sources */,

Tests/SwiftLintFrameworkTests/RulesTests.swift

@@ -52,6 +52,10 @@ class RulesTests: XCTestCase {
         verifyRule(CyclomaticComplexityRule.description)
     }
 
+    func testDiscardedNotificationCenterObserver() {
+        verifyRule(DiscardedNotificationCenterObserverRule.description)
+    }
+
     func testDynamicInline() {
         verifyRule(DynamicInlineRule.description)
     }
@@ -349,6 +353,7 @@ extension RulesTests {
             ("testConditionalReturnsOnNewline", testConditionalReturnsOnNewline),
             ("testControlStatement", testControlStatement),
             ("testCyclomaticComplexity", testCyclomaticComplexity),
+            ("testDiscardedNotificationCenterObserver", testDiscardedNotificationCenterObserver),
             ("testDynamicInline", testDynamicInline),
             ("testEmptyCount", testEmptyCount),
             ("testEmptyParameters", testEmptyParameters),