[4.1] Validate class constraints for generic arguments of types

include/swift/AST/DiagnosticsSema.def

@@ -1405,6 +1405,10 @@ NOTE(candidate_types_inheritance_requirement,none,
      (Type, Type, Type, Type, StringRef))
 NOTE(types_not_equal_requirement,none,
      "requirement specified as %0 == %1%2", (Type, Type, StringRef))
+ERROR(type_is_not_a_class,none,
+      "%0 requires that %1 be a class type", (Type, Type, Type))
+NOTE(anyobject_requirement,none,
+     "requirement specified as %0 : 'AnyObject'%2", (Type, Type, StringRef))
 ERROR(non_class_cannot_conform_to_class_protocol,none,
       "non-class type %0 cannot conform to class protocol %1",
       (Type, Type))

include/swift/AST/Types.h

@@ -670,6 +670,16 @@ class alignas(1 << TypeAlignInBits) TypeBase {
   /// with a class type.
   bool mayHaveSuperclass();
 
+  /// Determine whether this type satisfies a class layout constraint, written
+  /// `T: AnyObject` in the source.
+  ///
+  /// A class layout constraint is satisfied when we have a single retainable
+  /// pointer as the representation, which includes:
+  /// - @objc existentials
+  /// - class constrained archetypes
+  /// - classes
+  bool satisfiesClassConstraint();
+
   /// \brief Determine whether this type can be used as a base type for AST
   /// name lookup, which is the case for nominal types, protocol compositions
   /// and archetypes.

lib/AST/Type.cpp

@@ -1445,6 +1445,10 @@ bool TypeBase::mayHaveSuperclass() {
   return is<DynamicSelfType>();
 }
 
+bool TypeBase::satisfiesClassConstraint() {
+  return mayHaveSuperclass() || isObjCExistentialType();
+}
+
 Type TypeBase::getSuperclass() {
   auto *nominalDecl = getAnyNominal();
   auto *classDecl = dyn_cast_or_null<ClassDecl>(nominalDecl);

lib/SIL/TypeLowering.cpp

@@ -2290,10 +2290,8 @@ TypeConverter::checkForABIDifferences(SILType type1, SILType type2) {
   // Classes, class-constrained archetypes, and pure-ObjC existential types
   // all have single retainable pointer representation; optionality change
   // is allowed.
-  if ((type1.getSwiftRValueType()->mayHaveSuperclass() ||
-       type1.getSwiftRValueType()->isObjCExistentialType()) &&
-      (type2.getSwiftRValueType()->mayHaveSuperclass() ||
-       type2.getSwiftRValueType()->isObjCExistentialType()))
+  if (type1.getSwiftRValueType()->satisfiesClassConstraint() &&
+      type2.getSwiftRValueType()->satisfiesClassConstraint())
     return ABIDifference::Trivial;
 
   // Function parameters are ABI compatible if their differences are

lib/Sema/CSSimplify.cpp

@@ -1329,14 +1329,7 @@ ConstraintSystem::matchExistentialTypes(Type type1, Type type2,
   if (auto layoutConstraint = layout.getLayoutConstraint()) {
     if (layoutConstraint->isClass()) {
       if (kind == ConstraintKind::ConformsTo) {
-        // Conformance to AnyObject is defined by having a single
-        // retainable pointer representation:
-        //
-        // - @objc existentials
-        // - class constrained archetypes
-        // - classes
-        if (!type1->isObjCExistentialType() &&
-            !type1->mayHaveSuperclass())
+        if (!type1->satisfiesClassConstraint())
           return SolutionKind::Error;
       } else {
         // Subtype relation to AnyObject also allows class-bound

lib/Sema/TypeCheckConstraints.cpp

@@ -2827,9 +2827,7 @@ bool TypeChecker::checkedCastMaySucceed(Type t1, Type t2, DeclContext *dc) {
 
 bool TypeChecker::isSubstitutableFor(Type type, ArchetypeType *archetype,
                                      DeclContext *dc) {
-  if (archetype->requiresClass() &&
-      !type->mayHaveSuperclass() &&
-      !type->isObjCExistentialType())
+  if (archetype->requiresClass() && !type->satisfiesClassConstraint())
     return false;
 
   if (auto superclass = archetype->getSuperclass()) {

lib/Sema/TypeCheckGeneric.cpp

@@ -366,6 +366,8 @@ TypeChecker::gatherGenericParamBindingsText(
                                 TypeSubstitutionFn substitutions) {
   llvm::SmallPtrSet<GenericTypeParamType *, 2> knownGenericParams;
   for (auto type : types) {
+    if (type.isNull()) continue;
+
     type.visit([&](Type type) {
       if (auto gp = type->getAs<GenericTypeParamType>()) {
         knownGenericParams.insert(
@@ -1373,12 +1375,16 @@ RequirementCheckResult TypeChecker::checkGenericArguments(
         break;
       }
 
-      case RequirementKind::Layout: {
-        // TODO: Statically check if a the first type
-        // conforms to the layout constraint, once we
-        // support such static checks.
-        continue;
-      }
+      case RequirementKind::Layout:
+        // TODO: Statically check other layout constraints, once they can
+        // be spelled in Swift.
+        if (req.getLayoutConstraint()->isClass() &&
+            !firstType->satisfiesClassConstraint()) {
+          diagnostic = diag::type_is_not_a_class;
+          diagnosticNote = diag::anyobject_requirement;
+          requirementFailure = true;
+        }
+        break;
 
       case RequirementKind::Superclass:
         // Superclass requirements.

lib/Sema/TypeCheckProtocol.cpp

@@ -2692,11 +2692,9 @@ CheckTypeWitnessResult swift::checkTypeWitness(TypeChecker &tc, DeclContext *dc,
     }
   }
 
-  if (genericSig->requiresClass(depTy)) {
-    if (!contextType->isObjCExistentialType() &&
-        !contextType->mayHaveSuperclass())
-      return CheckTypeWitnessResult(tc.Context.getAnyObjectType());
-  }
+  if (genericSig->requiresClass(depTy) &&
+      !contextType->satisfiesClassConstraint())
+    return CheckTypeWitnessResult(tc.Context.getAnyObjectType());
 
   // Success!
   return CheckTypeWitnessResult();

lib/Sema/TypeCheckType.cpp

@@ -223,8 +223,7 @@ TypeChecker::getDynamicBridgedThroughObjCClass(DeclContext *dc,
                                                Type dynamicType,
                                                Type valueType) {
   // We can only bridge from class or Objective-C existential types.
-  if (!dynamicType->isObjCExistentialType() &&
-      !dynamicType->mayHaveSuperclass())
+  if (!dynamicType->satisfiesClassConstraint())
     return Type();
 
   // If the value type cannot be bridged, we're done.

test/Constraints/diagnostics.swift

@@ -234,8 +234,8 @@ String().asdf  // expected-error {{value of type 'String' has no member 'asdf'}}
 
 // <rdar://problem/21553065> Spurious diagnostic: '_' can only appear in a pattern or on the left side of an assignment
 protocol r21553065Protocol {}
-class r21553065Class<T : AnyObject> {}
-_ = r21553065Class<r21553065Protocol>()  // expected-error {{'r21553065Protocol' is not convertible to 'AnyObject'}}
+class r21553065Class<T : AnyObject> {} // expected-note{{requirement specified as 'T' : 'AnyObject'}}
+_ = r21553065Class<r21553065Protocol>()  // expected-error {{'r21553065Class' requires that 'r21553065Protocol' be a class type}}
 
 // Type variables not getting erased with nested closures
 struct Toe {

test/Constraints/generics.swift

@@ -265,7 +265,9 @@ protocol SubProto: BaseProto {}
 struct FullyGeneric<Foo> {} // expected-note 11 {{'Foo' declared as parameter to type 'FullyGeneric'}} expected-note 1 {{generic type 'FullyGeneric' declared here}}
 
 struct AnyClassBound<Foo: AnyObject> {} // expected-note {{'Foo' declared as parameter to type 'AnyClassBound'}} expected-note {{generic type 'AnyClassBound' declared here}}
+// expected-note@-1{{requirement specified as 'Foo' : 'AnyObject'}}
 struct AnyClassBound2<Foo> where Foo: AnyObject {} // expected-note {{'Foo' declared as parameter to type 'AnyClassBound2'}}
+// expected-note@-1{{requirement specified as 'Foo' : 'AnyObject' [with Foo = Any]}}
 
 struct ProtoBound<Foo: SubProto> {} // expected-note {{'Foo' declared as parameter to type 'ProtoBound'}} expected-note {{generic type 'ProtoBound' declared here}}
 struct ProtoBound2<Foo> where Foo: SubProto {} // expected-note {{'Foo' declared as parameter to type 'ProtoBound2'}}
@@ -301,11 +303,11 @@ func testFixIts() {
   _ = FullyGeneric<Any>()
 
   _ = AnyClassBound() // expected-error {{generic parameter 'Foo' could not be inferred}} expected-note {{explicitly specify the generic arguments to fix this issue}} {{20-20=<AnyObject>}}
-  _ = AnyClassBound<Any>() // expected-error {{'Any' is not convertible to 'AnyObject'}}
+  _ = AnyClassBound<Any>() // expected-error {{'AnyClassBound' requires that 'Any' be a class type}}
   _ = AnyClassBound<AnyObject>()
 
   _ = AnyClassBound2() // expected-error {{generic parameter 'Foo' could not be inferred}} expected-note {{explicitly specify the generic arguments to fix this issue}} {{21-21=<AnyObject>}}
-  _ = AnyClassBound2<Any>() // expected-error {{'Any' is not convertible to 'AnyObject'}}
+  _ = AnyClassBound2<Any>() // expected-error {{'AnyClassBound2' requires that 'Any' be a class type}}
   _ = AnyClassBound2<AnyObject>()
 
   _ = ProtoBound() // expected-error {{generic parameter 'Foo' could not be inferred}} expected-note {{explicitly specify the generic arguments to fix this issue}} {{17-17=<<#Foo: SubProto#>>}}

test/Generics/class_constraint.swift

@@ -0,0 +1,27 @@
+// RUN: %target-typecheck-verify-swift
+
+struct X<T: AnyObject> { } // expected-note 4{{requirement specified as 'T' : 'AnyObject'}}
+
+class C { }
+struct S { }
+
+protocol P { }
+
+let okay0: X<C>
+
+struct Y<T: AnyObject> {
+  let okay1: X<T>
+}
+
+struct Y2<T: C> {
+  let okay2: X<T>
+}
+
+let bad0: X<C & P> // expected-error{{'X' requires that 'C & P' be a class type}}
+let bad1: X<P> // expected-error{{'X' requires that 'P' be a class type}}
+let bad2: X<S> // expected-error{{'X' requires that 'S' be a class type}}
+
+struct Z<U> {
+  let bad3: X<U> // expected-error{{'X' requires that 'U' be a class type}}
+}
+

test/Generics/existential_restrictions.swift

@@ -53,17 +53,17 @@ class GP<T : P> {}
 class GOP<T : OP> {}
 class GCP<T : CP> {}
 class GSP<T : SP> {}
-class GAO<T : AnyObject> {}
+class GAO<T : AnyObject> {} // expected-note 2{{requirement specified as 'T' : 'AnyObject'}}
 
 func blackHole(_ t: Any) {}
 
 func testBindExistential() {
   blackHole(GP<P>()) // expected-error{{using 'P' as a concrete type conforming to protocol 'P' is not supported}}
   blackHole(GOP<OP>())
   blackHole(GCP<CP>()) // expected-error{{using 'CP' as a concrete type conforming to protocol 'CP' is not supported}}
-  blackHole(GAO<P>()) // expected-error{{'P' is not convertible to 'AnyObject'}}
+  blackHole(GAO<P>()) // expected-error{{'GAO' requires that 'P' be a class type}}
   blackHole(GAO<OP>())
-  blackHole(GAO<CP>()) // expected-error{{'CP' is not convertible to 'AnyObject'}}
+  blackHole(GAO<CP>()) // expected-error{{'GAO' requires that 'CP' be a class type}}
   blackHole(GSP<SP>()) // expected-error{{'SP' cannot be used as a type conforming to protocol 'SP' because 'SP' has static requirements}}
   blackHole(GAO<AnyObject>())
 }