[SE-0160] Warn about uses of @objc declarations that used deprecated @objc inference.

When in Swift 3 compatibility mode without
`-warn-swift3-objc-inference`, warn on the *uses* of declarations that
depend on the Objective-C runtime that became `@objc` due to the
deprecated inference rule. This far more directly captures important
uses of the deprecated Objective-C entrypoints. We diagnose:

* `#selector` expressions that refer to one of these `@objc` members
* `#keyPath` expressions that refer to one of these `@objc` members
* Dynamic lookup (i.e., member access via `AnyObject`) that refers to
  one of these `@objc` members.

Author: DougGregor

include/swift/AST/Attr.h

@@ -197,8 +197,12 @@ class DeclAttribute : public AttributeBase {
 
     /// Whether the name is implicit, produced as the result of caching.
     unsigned ImplicitName : 1;
+
+    /// Whether the @objc was inferred using Swift 3's deprecated inference
+    /// rules.
+    unsigned Swift3Inferred : 1;
   };
-  enum { NumObjCAttrBits = NumDeclAttrBits + 2 };
+  enum { NumObjCAttrBits = NumDeclAttrBits + 3 };
   static_assert(NumObjCAttrBits <= 32, "fits in an unsigned");
 
   class AccessibilityAttrBitFields {
@@ -716,6 +720,7 @@ class ObjCAttr final : public DeclAttribute,
   {
     ObjCAttrBits.HasTrailingLocationInfo = false;
     ObjCAttrBits.ImplicitName = implicitName;
+    ObjCAttrBits.Swift3Inferred = false;
 
     if (name) {
       NameData = name->getOpaqueValue();
@@ -823,6 +828,18 @@ class ObjCAttr final : public DeclAttribute,
     ObjCAttrBits.ImplicitName = implicit;
   }
 
+  /// Determine whether this attribute was inferred based on Swift 3's
+  /// deprecated @objc inference rules.
+  bool isSwift3Inferred() const {
+    return ObjCAttrBits.Swift3Inferred;
+  }
+
+  /// Set whether this attribute was inferred based on Swift 3's deprecated
+  /// @objc inference rules.
+  void setSwift3Inferred(bool inferred = true) {
+    ObjCAttrBits.Swift3Inferred = inferred;
+  }
+
   /// Clear the name of this entity.
   void clearName() {
     NameData = nullptr;

include/swift/AST/DiagnosticsSema.def

@@ -415,6 +415,10 @@ ERROR(expression_unused_keypath_result,none,
 ERROR(expr_keypath_non_objc_property,none,
       "argument of '#keyPath' refers to non-'@objc' property %0",
       (DeclName))
+WARNING(expr_keypath_swift3_objc_inference,none,
+        "argument of '#keyPath' refers to property %0 in %1 that depends on "
+        "'@objc' attribute inference deprecated in Swift 4",
+        (DeclName, Identifier))
 ERROR(stdlib_anyobject_not_found,none,
       "broken standard library: cannot find 'AnyObject' protocol", ())
 ERROR(expr_keypath_type_of_property,none,
@@ -463,6 +467,10 @@ ERROR(expr_selector_not_objc,none,
 NOTE(make_decl_objc,none,
      "add '@objc' to expose this %0 to Objective-C",
      (DescriptiveDeclKind))
+WARNING(expr_selector_swift3_objc_inference,none,
+        "argument of '#selector' refers to %0 %1 in %2 that depends on "
+        "'@objc' attribute inference deprecated in Swift 4",
+        (DescriptiveDeclKind, DeclName, Identifier))
 
 // Selectors-as-string-literals.
 WARNING(selector_literal_invalid,none,
@@ -1111,6 +1119,11 @@ WARNING(unsupported_synthesize_init_variadic,none,
 NOTE(variadic_superclass_init_here,none,
      "variadic superclass initializer defined here", ())
 
+WARNING(expr_dynamic_lookup_swift3_objc_inference,none,
+        "reference to %0 %1 of %2 depends on '@objc' attribute inference "
+        "deprecated in Swift 4",
+        (DescriptiveDeclKind, DeclName, Identifier))
+
 // Alignment attribute
 ERROR(alignment_not_power_of_two,none,
       "alignment value must be a power of two", ())

lib/AST/Attr.cpp

@@ -624,6 +624,7 @@ ObjCAttr::ObjCAttr(SourceLoc atLoc, SourceRange baseRange,
   }
 
   ObjCAttrBits.ImplicitName = false;
+  ObjCAttrBits.Swift3Inferred = false;
 }
 
 ObjCAttr *ObjCAttr::create(ASTContext &Ctx, Optional<ObjCSelector> name,
@@ -700,7 +701,9 @@ SourceLoc ObjCAttr::getRParenLoc() const {
 }
 
 ObjCAttr *ObjCAttr::clone(ASTContext &context) const {
-  return new (context) ObjCAttr(getName(), isNameImplicit());
+  auto attr = new (context) ObjCAttr(getName(), isNameImplicit());
+  attr->setSwift3Inferred(isSwift3Inferred());
+  return attr;
 }
 
 AvailableAttr *

lib/Sema/CSApply.cpp

@@ -910,6 +910,25 @@ namespace {
 
         closeExistential(ref, locator, /*force=*/openedExistential);
 
+        // If this attribute was inferred based on deprecated Swift 3 rules,
+        // complain.
+        if (auto attr = member->getAttrs().getAttribute<ObjCAttr>()) {
+          if (attr->isSwift3Inferred() &&
+              !tc.Context.LangOpts.WarnSwift3ObjCInference) {
+            tc.diagnose(memberLoc,
+                        diag::expr_dynamic_lookup_swift3_objc_inference,
+                        member->getDescriptiveKind(),
+                        member->getFullName(),
+                        member->getDeclContext()
+                          ->getAsNominalTypeOrNominalTypeExtensionContext()
+                          ->getName());
+            tc.diagnose(member, diag::make_decl_objc,
+                        member->getDescriptiveKind())
+              .fixItInsert(member->getAttributeInsertionLoc(false),
+                           "@objc ");
+          }
+        }
+
         return ref;
       }
 
@@ -3772,6 +3791,11 @@ namespace {
           return E;
         }
 
+        if (cs.getType(subExpr)->isLValueType()) {
+          // Treat this like a read of the property.
+          cs.propagateLValueAccessKind(subExpr, AccessKind::Read);
+        }
+
         // Check that we requested a property getter or setter.
         switch (E->getSelectorKind()) {
         case ObjCSelectorExpr::Method: {
@@ -3856,6 +3880,22 @@ namespace {
           .fixItInsert(foundDecl->getAttributeInsertionLoc(false),
                        "@objc ");
         return E;
+      } else if (auto attr = foundDecl->getAttrs().getAttribute<ObjCAttr>()) {
+        // If this attribute was inferred based on deprecated Swift 3 rules,
+        // complain.
+        if (attr->isSwift3Inferred() &&
+            !tc.Context.LangOpts.WarnSwift3ObjCInference) {
+          tc.diagnose(E->getLoc(), diag::expr_selector_swift3_objc_inference,
+                      foundDecl->getDescriptiveKind(), foundDecl->getFullName(),
+                      foundDecl->getDeclContext()
+                        ->getAsNominalTypeOrNominalTypeExtensionContext()
+                        ->getName())
+            .highlight(subExpr->getSourceRange());
+          tc.diagnose(foundDecl, diag::make_decl_objc,
+                      foundDecl->getDescriptiveKind())
+            .fixItInsert(foundDecl->getAttributeInsertionLoc(false),
+                         "@objc ");
+        }
       }
 
       // Note which method we're referencing.

lib/Sema/TypeCheckDecl.cpp

@@ -2771,7 +2771,17 @@ void swift::markAsObjC(TypeChecker &TC, ValueDecl *D,
       TC.diagnose(D, diag::objc_inference_swift3, *deprecatedReason)
         .highlight(dynamicLoc)
         .fixItInsert(D->getAttributeInsertionLoc(false), "@objc ");
-    };
+    }
+
+    // Mark the attribute as having used Swift 3 inference, or create an
+    // implicit @objc for that purpose.
+    auto attr = D->getAttrs().getAttribute<ObjCAttr>();
+    if (!attr) {
+      attr = ObjCAttr::createUnnamedImplicit(TC.Context);
+      D->getAttrs().add(attr);
+    }
+
+    attr->setSwift3Inferred();
   }
 }
 

lib/Sema/TypeCheckExprObjC.cpp

@@ -302,6 +302,20 @@ Optional<Type> TypeChecker::checkObjCKeyPathExpr(DeclContext *dc,
             .fixItInsert(var->getAttributeInsertionLoc(false),
                          "@objc ");
         }
+      } else if (auto attr = var->getAttrs().getAttribute<ObjCAttr>()) {
+        // If this attribute was inferred based on deprecated Swift 3 rules,
+        // complain.
+        if (attr->isSwift3Inferred() &&
+            !Context.LangOpts.WarnSwift3ObjCInference) {
+          diagnose(componentNameLoc, diag::expr_keypath_swift3_objc_inference,
+                   var->getFullName(),
+                   var->getDeclContext()
+                    ->getAsNominalTypeOrNominalTypeExtensionContext()
+                   ->getName());
+          diagnose(var, diag::make_decl_objc, var->getDescriptiveKind())
+            .fixItInsert(var->getAttributeInsertionLoc(false),
+                         "@objc ");
+        }
       } else {
         // FIXME: Warn about non-KVC-compliant getter/setter names?
       }

test/ClangImporter/objc_bridging_generics.swift

@@ -108,7 +108,7 @@ extension GenericClass {
   }
   // Doesn't use 'T', since its metadata isn't necessary to erase to AnyObject
   // or to existential metatype
-  func doesntUseGenericParam5(_ x: T, _ y: T.Type) -> T {
+  @objc func doesntUseGenericParam5(_ x: T, _ y: T.Type) -> T {
     _ = y as AnyObject.Type
     _ = y as Any.Type
     _ = y as AnyObject
@@ -143,10 +143,10 @@ extension GenericClass {
   // expected-error@+1{{extension of a generic Objective-C class cannot access the class's generic parameters}}
   func usesGenericParamJ() -> [(T, T)]? {} // expected-note{{used here}}
 
-  static func doesntUseGenericParam() {}
-  static func doesntUseGenericParam2() -> Self {}
+  @objc static func doesntUseGenericParam() {}
+  @objc static func doesntUseGenericParam2() -> Self {}
   // Doesn't technically use 'T', since it's type-erased at runtime
-  static func doesntUseGenericParam3() -> GenericClass<T> {}
+  @objc static func doesntUseGenericParam3() -> GenericClass<T> {}
 
   // expected-error@+1{{extension of a generic Objective-C class cannot access the class's generic parameters}}
   static func usesGenericParamC(_ x: [(T, T)]?) {} // expected-note{{used here}}
@@ -175,12 +175,12 @@ extension GenericClass {
 func swiftFunction<T: Animal>(x: T) {}
 
 extension AnimalContainer {
-  func doesntUseGenericParam1(_ x: T, _ y: T.Type) {
+  @objc func doesntUseGenericParam1(_ x: T, _ y: T.Type) {
     _ = #selector(x.another)
     _ = #selector(y.create)
   }
 
-  func doesntUseGenericParam2(_ x: T, _ y: T.Type) {
+  @objc func doesntUseGenericParam2(_ x: T, _ y: T.Type) {
     let a = x.another()
     _ = a.another()
     _ = x.another().another()
@@ -193,15 +193,15 @@ extension AnimalContainer {
     x.eat(a)
   }
 
-  func doesntUseGenericParam3(_ x: T, _ y: T.Type) {
+  @objc func doesntUseGenericParam3(_ x: T, _ y: T.Type) {
     let sup: Animal = x
     sup.eat(x)
     _ = x.buddy
     _ = x[0]
     x[0] = x
   }
 
-  func doesntUseGenericParam4(_ x: T, _ y: T.Type) {
+  @objc func doesntUseGenericParam4(_ x: T, _ y: T.Type) {
     _ = type(of: x).apexPredator.another()
     type(of: x).apexPredator = x
 
@@ -290,7 +290,7 @@ extension AnimalContainer {
 }
 
 extension PettableContainer {
-  func doesntUseGenericParam(_ x: T, _ y: T.Type) {
+  @objc func doesntUseGenericParam(_ x: T, _ y: T.Type) {
     // TODO: rdar://problem/27796375--allocating entry points are emitted as
     // true generics.
     // _ = type(of: x).init(fur: x).other()

test/Constraints/dynamic_lookup.swift

@@ -235,7 +235,7 @@ _ = anyDict["test"]!.bar() // expected-error {{value of type 'Any' has no member
 // looked-up dynamically through AnyObject are treated as conforming
 // to the protocols they are supposed to conform to.
 class NSObjDerived1 : NSObject {
-  var everything: [Any] = []
+  @objc var everything: [Any] = []
 }
 
 class NSObjDerived2 : NSObject {

test/Sema/availability_versions.swift

@@ -1310,7 +1310,7 @@ class Y {
 
 @objc
 class X {
-  var y = Y()
+  @objc var y = Y()
 }
 
 func testForFixitWithNestedMemberRefExpr() {

test/attr/attr_objc_swift3_deprecated.swift

@@ -14,3 +14,10 @@ class DynamicMembers {
   dynamic var bar: NSObject? = nil // expected-warning{{inference of '@objc' for 'dynamic' members is deprecated in Swift 4}}{{3-3=@objc }}
 }
 
+// Suppress diagnostices about references to inferred @objc declarations
+// in this mode.
+func test(sc: ObjCSubclass, dm: DynamicMembers) {
+  _ = #selector(sc.foo)
+  _ = #selector(getter: dm.bar)
+  _ = #keyPath(DynamicMembers.bar)
+}

test/attr/attr_objc_swift3_deprecated_uses.swift

@@ -0,0 +1,29 @@
+// RUN: %target-swift-frontend -disable-objc-attr-requires-foundation-module -typecheck -verify %s -swift-version 3
+// REQUIRES: objc_interop
+
+import Foundation
+
+class ObjCSubclass : NSObject {
+  func foo() { } // expected-note 2{{add '@objc' to expose this instance method to Objective-C}}{{3-3=@objc }}
+  var bar: NSObject? = nil // expected-note{{add '@objc' to expose this var to Objective-C}}{{3-3=@objc }}
+}
+
+class DynamicMembers {
+  dynamic func foo() { }
+  
+  dynamic var bar: NSObject? = nil // expected-note 2{{add '@objc' to expose this var to Objective-C}}{{3-3=@objc }}
+}
+
+func testSelector(sc: ObjCSubclass, dm: DynamicMembers) {
+  _ = #selector(sc.foo) // expected-warning{{argument of '#selector' refers to instance method 'foo()' in 'ObjCSubclass' that depends on '@objc' attribute inference deprecated in Swift 4}}
+  _ = #selector(getter: dm.bar) // expected-warning{{argument of '#selector' refers to var 'bar' in 'DynamicMembers' that depends on '@objc' attribute inference deprecated in Swift 4}}
+}
+
+func testKeypath(dm: DynamicMembers) {
+  _ = #keyPath(DynamicMembers.bar) // expected-warning{{argument of '#keyPath' refers to property 'bar' in 'DynamicMembers' that depends on '@objc' attribute inference deprecated in Swift 4}}
+}
+
+func testDynamicCalls(ao: AnyObject) {
+  ao.foo?() // expected-warning{{reference to instance method 'foo()' of 'ObjCSubclass' depends on '@objc' attribute inference deprecated in Swift 4}}
+  _ = ao.bar! // expected-warning{{reference to var 'bar' of 'ObjCSubclass' depends on '@objc' attribute inference deprecated in Swift 4}}
+}

test/expr/dynamic_lookup.swift

@@ -1,7 +1,7 @@
 // RUN: %target-typecheck-verify-swift
 
 @objc class HasStaticProperties {
-  class var staticVar1: Int { return 4 }
+  @objc class var staticVar1: Int { return 4 }
 }
 
 func testStaticProperty(classObj: AnyObject.Type) {

test/expr/unary/selector/Inputs/property_helper.swift

@@ -5,7 +5,7 @@ class OtherObjCClass: NSObject {
   @objc private(set) var privateSetVar = 2 // expected-note 2{{'privateSetVar' declared here}}
   @objc internal var internalVar = 2
 
-  internal func internalFunc() {}
+  @objc internal func internalFunc() {}
 
   private func privateFunc() {} // expected-note 2{{'privateFunc' declared here}}
 }

test/expr/unary/selector/property.swift

@@ -143,9 +143,9 @@ class ObjCClassWithGetterSetter: NSObject {
 // Looking up inherited members
 
 class BaseClass: NSObject {
-  var myVar = 1
+  @objc var myVar = 1
 
-  func myFunc() {
+  @objc func myFunc() {
   }
 }
 

test/expr/unary/selector/selector.swift

@@ -129,7 +129,7 @@ case #selector(C1.method1)?:
 }
 
 @objc class SR1827 {
-  func bar() {}
+  @objc func bar() {}
 }
 
 switch optionalSel {