[QoI] Don't emit @objc Fix-Its for cases where @objc will be inferred from a requirement.

This is a follow-up to the change that allowed one to omit @objc (or
the name in an @objc) when it can be inferred by matching a
requirement. There is no point in suggesting that one add @objc if it
will be inferred anyway, since it's just syntactic noise.

Author: DougGregor

include/swift/AST/Decl.h

@@ -2144,6 +2144,10 @@ class ValueDecl : public Decl {
   /// first slot.
   Optional<ObjCSelector> getObjCRuntimeName() const;
 
+  /// Determine whether the given declaration can infer @objc, or the
+  /// Objective-C name, if used to satisfy the given requirement.
+  bool canInferObjCFromRequirement(ValueDecl *requirement);
+
   SourceLoc getNameLoc() const { return NameLoc; }
   SourceLoc getLoc() const { return NameLoc; }
 

lib/AST/ASTContext.cpp

@@ -2479,8 +2479,9 @@ bool ASTContext::diagnoseObjCUnsatisfiedOptReqConflicts(SourceFile &sf) {
       fixDeclarationName(diag, conflicts[0], req->getFullName());
 
       // Fix the '@objc' attribute, if needed.
-      fixDeclarationObjCName(diag, conflicts[0], req->getObjCRuntimeName(),
-                             /*ignoreImpliedName=*/true);
+      if (!conflicts[0]->canInferObjCFromRequirement(req))
+        fixDeclarationObjCName(diag, conflicts[0], req->getObjCRuntimeName(),
+                               /*ignoreImpliedName=*/true);
     }
 
     // @nonobjc will silence this warning.

lib/AST/Decl.cpp

@@ -1736,6 +1736,42 @@ Optional<ObjCSelector> ValueDecl::getObjCRuntimeName() const {
   return None;
 }
 
+bool ValueDecl::canInferObjCFromRequirement(ValueDecl *requirement) {
+  // Only makes sense for a requirement of an @objc protocol.
+  auto proto = cast<ProtocolDecl>(requirement->getDeclContext());
+  if (!proto->isObjC()) return false;
+
+  // Only makes sense when this declaration is within a nominal type
+  // or extension thereof.
+  auto nominal =
+    getDeclContext()->getAsNominalTypeOrNominalTypeExtensionContext();
+  if (!nominal) return false;
+
+  // If there is already an @objc attribute with an explicit name, we
+  // can't infer a name (it's already there).
+  if (auto objcAttr = getAttrs().getAttribute<ObjCAttr>()) {
+    if (!objcAttr->isNameImplicit()) return false;
+  }
+
+  // If the nominal type doesn't conform to the protocol at all, we
+  // cannot infer @objc no matter what we do.
+  SmallVector<ProtocolConformance *, 1> conformances;
+  if (!nominal->lookupConformance(getModuleContext(), proto, conformances))
+    return false;
+
+  // If any of the conformances is attributed to the context in which
+  // this declaration resides, we can infer @objc or the Objective-C
+  // name.
+  auto dc = getDeclContext();
+  for (auto conformance : conformances) {
+    if (conformance->getDeclContext() == dc)
+      return true;
+  }
+
+  // Nothing to infer from.
+  return false;
+}
+
 SourceLoc ValueDecl::getAttributeInsertionLoc(bool forModifier) const {
   if (auto var = dyn_cast<VarDecl>(this)) {
     if (auto pbd = var->getParentPatternBinding()) {

lib/Sema/TypeCheckProtocol.cpp

@@ -1718,7 +1718,7 @@ diagnoseMatch(TypeChecker &tc, Module *module,
     fixDeclarationName(diag, match.Witness, req->getFullName());
 
     // Also fix the Objective-C name, if needed.
-    if (req->isObjC())
+    if (!match.Witness->canInferObjCFromRequirement(req))
       fixDeclarationObjCName(diag, match.Witness, req->getObjCRuntimeName());
     break;
   }
@@ -3665,9 +3665,11 @@ void ConformanceChecker::checkConformance() {
                                                : diag::witness_non_objc,
                                     diagInfo.first, diagInfo.second,
                                     Proto->getFullName());
-            fixDeclarationObjCName(
-              diag, witness,
-              cast<AbstractFunctionDecl>(requirement)->getObjCSelector());
+            if (!witness->canInferObjCFromRequirement(requirement)) {
+              fixDeclarationObjCName(
+                diag, witness,
+                cast<AbstractFunctionDecl>(requirement)->getObjCSelector());
+            }
           } else if (isa<VarDecl>(witness)) {
             auto diag = TC.diagnose(witness,
                                     isOptional
@@ -3676,10 +3678,13 @@ void ConformanceChecker::checkConformance() {
                                     /*isSubscript=*/false,
                                     witness->getFullName(),
                                     Proto->getFullName());
-            fixDeclarationObjCName(
-               diag, witness,
-               ObjCSelector(requirement->getASTContext(), 0,
-                            cast<VarDecl>(requirement)->getObjCPropertyName()));
+            if (!witness->canInferObjCFromRequirement(requirement)) {
+              fixDeclarationObjCName(
+                 diag, witness,
+                 ObjCSelector(requirement->getASTContext(), 0,
+                              cast<VarDecl>(requirement)
+                                ->getObjCPropertyName()));
+            }
           } else if (isa<SubscriptDecl>(witness)) {
             TC.diagnose(witness,
                         isOptional
@@ -4412,7 +4417,8 @@ static void diagnosePotentialWitness(TypeChecker &tc,
     // Special case: note to add @objc.
     auto diag = tc.diagnose(witness,
                             diag::optional_req_nonobjc_near_match_add_objc);
-    fixDeclarationObjCName(diag, witness, req->getObjCRuntimeName());
+    if (!witness->canInferObjCFromRequirement(req))
+      fixDeclarationObjCName(diag, witness, req->getObjCRuntimeName());
   } else {
     diagnoseMatch(tc, conformance->getDeclContext()->getParentModule(),
                   conformance, req, match);

test/ClangModules/objc_parse.swift

@@ -265,7 +265,7 @@ func classAnyObject(_ obj: NSObject) {
 class Wobbler : NSWobbling { // expected-note{{candidate has non-matching type '()'}}
   @objc func wobble() { }
 
-  func returnMyself() -> Self { return self } // expected-error{{non-'@objc' method 'returnMyself()' does not satisfy requirement of '@objc' protocol 'NSWobbling'}}{{3-3=@objc }}
+  func returnMyself() -> Self { return self } // expected-error{{non-'@objc' method 'returnMyself()' does not satisfy requirement of '@objc' protocol 'NSWobbling'}}{{none}}
   // expected-error@-1{{method cannot be an implementation of an @objc requirement because its result type cannot be represented in Objective-C}}
 }
 

test/decl/protocol/conforms/near_miss_objc.swift

@@ -10,7 +10,7 @@
 class C1a : P1 {
   @objc func doSomething(a: Int, c: Double) { }
   // expected-warning@-1{{instance method 'doSomething(a:c:)' nearly matches optional requirement 'doSomething(a:b:)' of protocol 'P1'}}
-  // expected-note@-2{{rename to 'doSomething(a:b:)' to satisfy this requirement}}{{34-34=b }}{{8-8=(doSomethingWithA:b:)}}
+  // expected-note@-2{{rename to 'doSomething(a:b:)' to satisfy this requirement}}{{34-34=b }}{{none}}
   // expected-note@-3{{move 'doSomething(a:c:)' to an extension to silence this warning}}
   // expected-note@-4{{make 'doSomething(a:c:)' private to silence this warning}}{{9-9=private }}
 }
@@ -28,7 +28,7 @@ class C1c {
 extension C1c : P1 {
   func doSomething(a: Int, c: Double) { }
   // expected-warning@-1{{instance method 'doSomething(a:c:)' nearly matches optional requirement 'doSomething(a:b:)' of protocol 'P1'}}
-  // expected-note@-2{{rename to 'doSomething(a:b:)' to satisfy this requirement}}{{28-28=b }}{{3-3=@objc(doSomethingWithA:b:) }}
+  // expected-note@-2{{rename to 'doSomething(a:b:)' to satisfy this requirement}}{{28-28=b }}{{none}}
   // expected-note@-3{{move 'doSomething(a:c:)' to another extension to silence this warning}}
   // expected-note@-4{{make 'doSomething(a:c:)' private to silence this warning}}{{3-3=private }}
 }
@@ -87,7 +87,7 @@ class C4a : P4 {
 class C5a : P5 {
   func method(_: Int, for someClass: SomeClass, dividing double: Double) { }
   // expected-warning@-1{{instance method 'method(_:for:dividing:)' nearly matches optional requirement 'methodWithInt(_:forSomeClass:dividingDouble:)' of protocol 'P5'}}
-  // expected-note@-2{{rename to 'methodWithInt(_:forSomeClass:dividingDouble:)' to satisfy this requirement}}{{3-3=@objc(methodWithInt:forSomeClass:dividingDouble:) }}{{8-14=methodWithInt}}{{23-26=forSomeClass}}{{49-57=dividingDouble}}
+  // expected-note@-2{{rename to 'methodWithInt(_:forSomeClass:dividingDouble:)' to satisfy this requirement}}{{8-14=methodWithInt}}{{23-26=forSomeClass}}{{49-57=dividingDouble}}{{none}}
   // expected-note@-3{{move 'method(_:for:dividing:)' to an extension to silence this warning}}
   // expected-note@-4{{make 'method(_:for:dividing:)' private to silence this warning}}{{3-3=private }}
 }
@@ -100,7 +100,7 @@ class C5a : P5 {
 class C6a : P6 {
   func methodWithInt(_: Int, forSomeClass: SomeClass, dividingDouble: Double) { }
   // expected-warning@-1{{instance method 'methodWithInt(_:forSomeClass:dividingDouble:)' nearly matches optional requirement 'method(_:for:dividing:)' of protocol 'P6'}}
-  // expected-note@-2{{rename to 'method(_:for:dividing:)' to satisfy this requirement}}{{3-3=@objc(method:for:dividing:) }}{{8-21=method}}{{30-30=for }}{{55-55=dividing }}
+  // expected-note@-2{{rename to 'method(_:for:dividing:)' to satisfy this requirement}}{{8-21=method}}{{30-30=for }}{{55-55=dividing }}{{none}}
   // expected-note@-3{{move 'methodWithInt(_:forSomeClass:dividingDouble:)' to an extension to silence this warning}}
   // expected-note@-4{{make 'methodWithInt(_:forSomeClass:dividingDouble:)' private to silence this warning}}{{3-3=private }}
 }

test/decl/protocol/req/optional.swift

@@ -117,7 +117,7 @@ extension C6 : P1 {
 @objc class C8 : P2 { // expected-note{{class 'C8' declares conformance to protocol 'P2' here}}
   func objcMethod(int x: Int) { } // expected-error{{Objective-C method 'objcMethodWithInt:' provided by method 'objcMethod(int:)' conflicts with optional requirement method 'method(y:)' in protocol 'P2'}}
   // expected-note@-1{{add '@nonobjc' to silence this error}}{{3-3=@nonobjc }}
-  // expected-note@-2{{rename method to match requirement 'method(y:)'}}{{3-3=@objc(objcMethodWithInt:) }}{{8-18=method}}{{19-22=y}}
+  // expected-note@-2{{rename method to match requirement 'method(y:)'}}{{8-18=method}}{{19-22=y}}{{none}}
 }