Check protocols for selector conflicts

Although we have always checked classes to see if their @objc members had the same selectors, it turns out we never did this for protocols. Oops. Keep a table of ObjC selector names for protocols, just as we do for classes, and diagnose any conflicts between them.

Fixes rdar://80990066.

Author: beccadax

lib/AST/NameLookup.cpp

@@ -1487,7 +1487,7 @@ bool NominalTypeDecl::createObjCMethodLookup() {
   assert(!ObjCMethodLookup && "Already have an Objective-C member table");
 
   // Most types cannot have ObjC methods.
-  if (!(isa<ClassDecl>(this)))
+  if (!(isa<ClassDecl>(this) || isa<ProtocolDecl>(this)))
     return false;
 
   auto &ctx = getASTContext();

lib/Sema/TypeCheckDeclObjC.cpp

@@ -2447,6 +2447,7 @@ bool swift::diagnoseObjCMethodConflicts(SourceFile &sf) {
   // Diagnose each conflict.
   bool anyConflicts = false;
   for (const auto &conflict : localConflicts) {
+    NominalTypeDecl *tyDecl = std::get<0>(conflict);
     ObjCSelector selector = std::get<1>(conflict);
 
     auto methods = getObjCMethodConflictDecls(conflict);
@@ -2530,6 +2531,9 @@ bool swift::diagnoseObjCMethodConflicts(SourceFile &sf) {
                                      origDiagInfo.first, origDiagInfo.second,
                                      selector);
 
+      // Protocols weren't checked for selector conflicts in 5.0.
+      diag.warnUntilSwiftVersionIf(!isa<ClassDecl>(tyDecl), 6);
+
       auto objcAttr = getObjCAttrIfFromAccessNote(conflictingDecl);
       swift::softenIfAccessNote(conflictingDecl, objcAttr, diag);
       if (objcAttr)

test/ClangImporter/objc_bridging_custom.swift

@@ -159,8 +159,9 @@ protocol TestProto {
   @objc optional func testUnmigrated(a: NSRuncingMode, b: Refrigerator, c: NSCoding) // expected-note {{here}} {{none}}
   @objc optional func testPartialMigrated(a: NSRuncingMode, b: Refrigerator) // expected-note {{here}} {{none}}
 
-  @objc optional subscript(a a: Refrigerator) -> Refrigerator? { get } // expected-note {{here}} {{none}}
+  @objc optional subscript(a a: Refrigerator) -> Refrigerator? { get } // expected-note 2 {{here}} {{none}}
   @objc optional subscript(generic a: ManufacturerInfo<NSString>) -> ManufacturerInfo<NSString>? { get } // expected-note {{here}} {{none}}
+  // expected-warning@-1 {{subscript getter with Objective-C selector 'objectForKeyedSubscript:' conflicts with previous declaration with the same Objective-C selector; this is an error in Swift 6}}
 
   @objc optional var prop: Refrigerator? { get } // expected-note {{here}} {{none}}
   @objc optional var propGeneric: ManufacturerInfo<NSString>? { get } // expected-note {{here}} {{none}}

test/Constraints/common_type_objc.swift

@@ -6,11 +6,11 @@
 import Foundation
 
 @objc protocol P {
-  func foo(_ i: Int) -> Double
-  func foo(_ d: Double) -> Double
+  func foo(_ i: Int) -> Double // expected-note {{'foo' previously declared here}}
+  func foo(_ d: Double) -> Double // expected-warning {{method 'foo' with Objective-C selector 'foo:' conflicts with previous declaration with the same Objective-C selector; this is an error in Swift 6}}
 
-  @objc optional func opt(_ i: Int) -> Int
-  @objc optional func opt(_ d: Double) -> Int
+  @objc optional func opt(_ i: Int) -> Int // expected-note {{'opt' previously declared here}}
+  @objc optional func opt(_ d: Double) -> Int // expected-warning {{method 'opt' with Objective-C selector 'opt:' conflicts with previous declaration with the same Objective-C selector; this is an error in Swift 6}}
 }
 
 func testOptional(obj: P) {

test/Constraints/overload_filtering_objc.swift

@@ -9,8 +9,8 @@
 import Foundation
 
 @objc protocol P {
-  func foo(_ i: Int) -> Int
-  func foo(_ d: Double) -> Int
+  func foo(_ i: Int) -> Int // expected-note {{'foo' previously declared here}}
+  func foo(_ d: Double) -> Int // expected-warning {{method 'foo' with Objective-C selector 'foo:' conflicts with previous declaration with the same Objective-C selector; this is an error in Swift 6}}
 
   @objc optional func opt(_ i: Int) -> Int
   @objc optional func opt(double: Double) -> Int

test/attr/attr_objc.swift

@@ -364,9 +364,11 @@ protocol subject_containerObjCProtocol1 {
 @objc // access-note-move{{subject_containerObjCProtocol2}}
 protocol subject_containerObjCProtocol2 {
   init(a: Int)
+  // expected-note@-1 {{'init' previously declared here}}
 
   @objc // FIXME: Access notes can't distinguish between init(a:) overloads
   init(a: Double)
+  // expected-warning@-1 {{initializer 'init(a:)' with Objective-C selector 'initWithA:' conflicts with previous declaration with the same Objective-C selector; this is an error in Swift 6}}
 
   func func1() -> Int
   @objc // access-note-move{{subject_containerObjCProtocol2.func1_()}}

test/decl/protocol/objc.swift

@@ -258,3 +258,10 @@ class C8SubRW: C8Base {
 class C8SubRW2: C8Base {
   var prop: Int = 0
 }
+
+@available(macOS 12, iOS 15, tvOS 15, watchOS 8, *)
+@objc protocol P9 {
+  @objc(custom:) func f(_: Any) // expected-note 2 {{method 'f' declared here}}
+  @objc(custom:) func g(_: Any) // expected-warning {{method 'g' with Objective-C selector 'custom:' conflicts with method 'f' with the same Objective-C selector; this is an error in Swift 6}}
+  @objc(custom:) func h() async // expected-warning {{method 'h()' with Objective-C selector 'custom:' conflicts with method 'f' with the same Objective-C selector; this is an error in Swift 6}}
+}