Don’t require @optional ObjC methods in @objcImpl

rdar://108461441

Author: beccadax

lib/Sema/TypeCheckDeclObjC.cpp

@@ -28,6 +28,9 @@
 #include "swift/AST/SourceFile.h"
 #include "swift/AST/TypeCheckRequests.h"
 #include "swift/Basic/StringExtras.h"
+
+#include "clang/AST/DeclObjC.h"
+
 using namespace swift;
 
 #pragma mark Determine whether an entity is representable in Objective-C.
@@ -3326,9 +3329,25 @@ class ObjCImplementationChecker {
     return Identifier();
   }
 
+  /// Is this member an `@optional` ObjC protocol requirement?
+  static bool isOptionalObjCProtocolRequirement(ValueDecl *vd) {
+    if (auto clangDecl = vd->getClangDecl()) {
+      if (auto method = dyn_cast<clang::ObjCMethodDecl>(clangDecl))
+        return method->isOptional();
+      if (auto property = dyn_cast<clang::ObjCPropertyDecl>(clangDecl))
+        return property->isOptional();
+    }
+
+    return false;
+  }
+
 public:
   void diagnoseUnmatchedRequirements() {
     for (auto req : unmatchedRequirements) {
+      // Ignore `@optional` protocol requirements.
+      if (isOptionalObjCProtocolRequirement(req))
+        continue;
+
       auto ext = cast<IterableDeclContext>(req->getDeclContext()->getAsDecl())
                         ->getImplementationContext();
 

test/decl/ext/Inputs/objc_implementation.h

@@ -91,6 +91,21 @@
 - (void)doSomethingFunAndAsynchronousWithCompletionHandler:(void (^ _Nonnull)(id _Nullable result, NSError * _Nullable error))completionHandler;
 @end
 
+@protocol PartiallyOptionalProtocol
+
+- (void)requiredMethod1;
+- (void)requiredMethod2;
+
+@optional
+- (void)optionalMethod1;
+- (void)optionalMethod2;
+
+@end
+
+@interface ObjCClass (Conformance) <PartiallyOptionalProtocol>
+
+@end
+
 @interface ObjCSubclass : ObjCClass
 
 - (void)subclassMethodFromHeader1:(int)param;

test/decl/ext/objc_implementation.swift

@@ -291,6 +291,15 @@
   }
 }
 
+@_objcImplementation(Conformance) extension ObjCClass {
+  // expected-error@-1 {{extension for category 'Conformance' should provide implementation for instance method 'requiredMethod2()'}}
+  // no-error concerning 'optionalMethod2()'
+
+  func requiredMethod1() {}
+
+  func optionalMethod1() {}
+}
+
 @_objcImplementation extension ObjCClass {}
 // expected-error@-1 {{duplicate implementation of Objective-C class 'ObjCClass'}}