Handle inherited required inits in @objcImpl

Because `required init`s do not have the `override` keyword, they are always treated as member implementations (if they pass other checks). However, these methods sometimes actually are overrides, and when they are, they should not be treated as member implementations. This results in required inits being treated as candidates when there won’t be a requirement for them to match.

Hack around this by separately checking for this situation and skipping the affected members.

Fixes rdar://112910098.

Author: beccadax

lib/Sema/TypeCheckDeclObjC.cpp

@@ -3507,6 +3507,15 @@ class ObjCImplementationChecker {
     for (auto &pair : unmatchedCandidates) {
       auto cand = pair.first;
 
+      // `isObjCMemberImplementation()` incorrectly returns true for required
+      // inits that are overrides because checking in that accessor would create
+      // a cycle between override computations and access control. Don't
+      // diagnose such candidates.
+      // FIXME: Refactor around this so these methods are never made candidates.
+      if (auto ctor = dyn_cast<ConstructorDecl>(cand))
+        if (ctor->isRequired() && !ctor->getOverriddenDecls().empty())
+          continue;
+
       diagnose(cand, diag::member_of_objc_implementation_not_objc_or_final,
                cand, cand->getDeclContext()->getSelfClassDecl());
 

test/decl/ext/Inputs/objc_implementation.h

@@ -157,6 +157,12 @@
 
 @end
 
+@interface ObjCImplSubclass : ObjCClass
+
+@end
+
+
+
 struct ObjCStruct {
   int foo;
 };

test/decl/ext/objc_implementation.swift

@@ -386,6 +386,13 @@ protocol EmptySwiftProto {}
   func nonPointerArgument(_: CInt!) {} // expected-error {{method cannot be implicitly @objc because the type of the parameter cannot be represented in Objective-C}}
 }
 
+@_objcImplementation extension ObjCImplSubclass {
+    @objc(initFromProtocol1:)
+    required public init?(fromProtocol1: CInt) {
+      // OK
+    }
+}
+
 @_objcImplementation extension ObjCClass {}
 // expected-error@-1 {{duplicate implementation of Objective-C class 'ObjCClass'}}