Fix false alarms in `redundant_objc_attribute` rule (#4742)

CHANGELOG.md

@@ -32,6 +32,11 @@
   [SimplyDanny](https://github.com/SimplyDanny)
   [#5009](https://github.com/realm/SwiftLint/issues/5009)
 
+* Fix false positives on `redundant_objc_attribute` rule for enums
+  and private members.  
+  [Martin Redington](https://github.com/mildm8nnered)
+  [#4633](https://github.com/realm/SwiftLint/issues/4633)
+
 * Fix autocorrect for `CGIntersectionRect` in `legacy_cggeometry_functions`
   rule.  
   [Haoocen](https://github.com/Haoocen)

Source/SwiftLintBuiltInRules/Rules/Idiomatic/RedundantObjcAttributeRule.swift

@@ -68,6 +68,15 @@ private extension Syntax {
             return false
         }
     }
+
+    var functionOrVariableModifiers: ModifierListSyntax? {
+        if let functionDecl = self.as(FunctionDeclSyntax.self) {
+            return functionDecl.modifiers
+        } else if let variableDecl = self.as(VariableDeclSyntax.self) {
+            return variableDecl.modifiers
+        }
+        return nil
+    }
 }
 
 private extension AttributeListSyntax {
@@ -78,10 +87,12 @@ private extension AttributeListSyntax {
 
         if hasAttributeImplyingObjC, parent?.is(ExtensionDeclSyntax.self) != true {
             return objcAttribute
+        } else if parent?.is(EnumDeclSyntax.self) == true {
+            return nil
         } else if parent?.isFunctionOrStoredProperty == true,
                   let parentClassDecl = parent?.parent?.parent?.parent?.parent?.as(ClassDeclSyntax.self),
                   parentClassDecl.attributes.contains(attributeNamed: "objcMembers") {
-            return objcAttribute
+            return parent?.functionOrVariableModifiers.isPrivateOrFileprivate == true ? nil : objcAttribute
         } else if let parentExtensionDecl = parent?.parent?.parent?.parent?.parent?.as(ExtensionDeclSyntax.self),
                   parentExtensionDecl.attributes?.objCAttribute != nil {
             return objcAttribute

Source/SwiftLintBuiltInRules/Rules/Idiomatic/RedundantObjcAttributeRuleExamples.swift

@@ -13,7 +13,7 @@ struct RedundantObjcAttributeRuleExamples {
         class Foo {
             var bar: Any?
             @objc
-            class Bar {
+            class Bar: NSObject {
                 @objc
                 var foo: Any?
             }
@@ -59,14 +59,15 @@ struct RedundantObjcAttributeRuleExamples {
         Example("""
         @objcMembers
         class Foo {
+            @objc
             class Bar: NSObject {
-                @objc var foo: Any
+                @objc var foo: Any?
             }
         }
         """),
         Example("""
         @objcMembers
-        class Foo {
+        class Foo: NSObject {
             @objc class Bar {}
         }
         """),
@@ -75,6 +76,59 @@ struct RedundantObjcAttributeRuleExamples {
             @objc(addElementsObject:)
             @NSManaged public func addToElements(_ value: BlockEditorSettingElement)
         }
+        """),
+        Example("""
+        @objcMembers
+        public class Foo: NSObject {
+            @objc
+            private func handler(_ notification: Notification) {
+            }
+
+            func registerForNotifications() {
+                NotificationCenter.default.addObserver(self, selector: #selector(handler(_:)), name: nil, object: nil)
+            }
+        }
+        """),
+        Example("""
+        class Foo: NSObject { }
+
+        @objc extension Foo {
+            @objc enum Bar: Int {
+               case bar
+            }
+
+            var bar: Bar { .bar }
+        }
+        """),
+        Example("""
+        class Foo: NSObject { }
+
+        @objc extension Foo {
+            @objc private enum Baz: Int {
+              case baz
+            }
+
+            private var baz: Baz { .baz }
+        }
+        """),
+        Example("""
+        @objcMembers
+        internal class Foo: NSObject {
+            @objc
+            private var baz: Int = 1
+
+            var x: Any? {
+                value(forKey: "baz")
+            }
+        }
+        """),
+        Example("""
+        @objcMembers
+        class Foo: NSObject {
+            @objc enum Bar: Int {
+               case bar
+            }
+        }
         """)
     ]
 
@@ -90,13 +144,13 @@ struct RedundantObjcAttributeRuleExamples {
         Example("↓@objc @IBDesignable class Foo {}"),
         Example("""
         @objcMembers
-        class Foo {
+        class Foo: NSObject {
             ↓@objc var bar: Any?
         }
         """),
         Example("""
         @objcMembers
-        class Foo {
+        class Foo: NSObject {
             ↓@objc var bar: Any?
             ↓@objc var foo: Any?
             @objc
@@ -126,7 +180,7 @@ struct RedundantObjcAttributeRuleExamples {
         """),
         Example("""
         @objcMembers
-        class Foo {
+        class Foo: NSObject {
             @objcMembers
             class Bar: NSObject {
                 ↓@objc var foo: Any
@@ -160,23 +214,23 @@ struct RedundantObjcAttributeRuleExamples {
         Example("↓@objc @IBDesignable class Foo {}"): Example("@IBDesignable class Foo {}"),
         Example("""
         @objcMembers
-        class Foo {
+        class Foo: NSObject {
             ↓@objc var bar: Any?
         }
         """):
         Example("""
         @objcMembers
-        class Foo {
+        class Foo: NSObject {
             var bar: Any?
         }
         """),
         Example("""
         @objcMembers
-        class Foo {
+        class Foo: NSObject {
             ↓@objc var bar: Any?
             ↓@objc var foo: Any?
             @objc
-            class Bar {
+            class Bar: NSObject {
                 @objc
                 var foo2: Any?
             }
@@ -184,11 +238,11 @@ struct RedundantObjcAttributeRuleExamples {
         """):
         Example("""
         @objcMembers
-        class Foo {
+        class Foo: NSObject {
             var bar: Any?
             var foo: Any?
             @objc
-            class Bar {
+            class Bar: NSObject {
                 @objc
                 var foo2: Any?
             }
@@ -230,7 +284,7 @@ struct RedundantObjcAttributeRuleExamples {
         """),
         Example("""
         @objcMembers
-        class Foo {
+        class Foo: NSObject {
             @objcMembers
             class Bar: NSObject {
                 ↓@objc var foo: Any
@@ -239,7 +293,7 @@ struct RedundantObjcAttributeRuleExamples {
         """):
         Example("""
         @objcMembers
-        class Foo {
+        class Foo: NSObject {
             @objcMembers
             class Bar: NSObject {
                 var foo: Any