Sema: Introduce ConstraintKind::SubclassOf

Author: slavapestov

include/swift/Sema/Constraint.h

@@ -97,6 +97,9 @@ enum class ConstraintKind : char {
   ArgumentConversion,
   /// The first type is convertible to the second type, including inout.
   OperatorArgumentConversion,
+  /// The first type must be a subclass of the second type (which is a
+  /// class type).
+  SubclassOf,
   /// The first type must conform to the second type (which is a
   /// protocol type).
   ConformsTo,
@@ -669,6 +672,7 @@ class Constraint final : public llvm::ilist_node<Constraint>,
     case ConstraintKind::BridgingConversion:
     case ConstraintKind::ArgumentConversion:
     case ConstraintKind::OperatorArgumentConversion:
+    case ConstraintKind::SubclassOf:
     case ConstraintKind::ConformsTo:
     case ConstraintKind::LiteralConformsTo:
     case ConstraintKind::TransitivelyConformsTo:

include/swift/Sema/ConstraintSystem.h

@@ -5423,6 +5423,15 @@ class ConstraintSystem {
                                               FunctionRefKind functionRefKind,
                                               ConstraintLocator *locator);
 
+  /// Attempt to simplify the given superclass constraint.
+  ///
+  /// \param type The type being tested.
+  /// \param classType The class type which the type should be a subclass of.
+  /// \param locator Locator describing where this constraint occurred.
+  SolutionKind simplifySubclassOfConstraint(Type type, Type classType,
+                                            ConstraintLocatorBuilder locator,
+                                            TypeMatchOptions flags);
+
   /// Attempt to simplify the given conformance constraint.
   ///
   /// \param type The type being tested.

lib/Sema/CSBindings.cpp

@@ -1281,6 +1281,7 @@ PotentialBindings::inferFromRelational(Constraint *constraint) {
 
     switch (constraint->getKind()) {
     case ConstraintKind::Subtype:
+    case ConstraintKind::SubclassOf:
     case ConstraintKind::Conversion:
     case ConstraintKind::ArgumentConversion:
     case ConstraintKind::OperatorArgumentConversion: {
@@ -1358,6 +1359,7 @@ void PotentialBindings::infer(Constraint *constraint) {
   case ConstraintKind::BindParam:
   case ConstraintKind::BindToPointerType:
   case ConstraintKind::Subtype:
+  case ConstraintKind::SubclassOf:
   case ConstraintKind::Conversion:
   case ConstraintKind::ArgumentConversion:
   case ConstraintKind::OperatorArgumentConversion:

lib/Sema/CSSimplify.cpp

@@ -2362,6 +2362,7 @@ ConstraintSystem::matchTupleTypes(TupleType *tuple1, TupleType *tuple2,
   case ConstraintKind::DynamicCallableApplicableFunction:
   case ConstraintKind::BindOverload:
   case ConstraintKind::CheckedCast:
+  case ConstraintKind::SubclassOf:
   case ConstraintKind::ConformsTo:
   case ConstraintKind::TransitivelyConformsTo:
   case ConstraintKind::Defaultable:
@@ -2534,6 +2535,7 @@ static bool matchFunctionRepresentations(FunctionType::ExtInfo einfo1,
   case ConstraintKind::DynamicCallableApplicableFunction:
   case ConstraintKind::BindOverload:
   case ConstraintKind::CheckedCast:
+  case ConstraintKind::SubclassOf:
   case ConstraintKind::ConformsTo:
   case ConstraintKind::TransitivelyConformsTo:
   case ConstraintKind::Defaultable:
@@ -2948,6 +2950,7 @@ ConstraintSystem::matchFunctionTypes(FunctionType *func1, FunctionType *func2,
   case ConstraintKind::DynamicCallableApplicableFunction:
   case ConstraintKind::BindOverload:
   case ConstraintKind::CheckedCast:
+  case ConstraintKind::SubclassOf:
   case ConstraintKind::ConformsTo:
   case ConstraintKind::TransitivelyConformsTo:
   case ConstraintKind::Defaultable:
@@ -6255,6 +6258,7 @@ ConstraintSystem::matchTypes(Type type1, Type type2, ConstraintKind kind,
     case ConstraintKind::BindOverload:
     case ConstraintKind::BridgingConversion:
     case ConstraintKind::CheckedCast:
+    case ConstraintKind::SubclassOf:
     case ConstraintKind::ConformsTo:
     case ConstraintKind::TransitivelyConformsTo:
     case ConstraintKind::Defaultable:
@@ -7314,6 +7318,99 @@ ConstraintSystem::simplifyConstructionConstraint(
   return SolutionKind::Solved;
 }
 
+ConstraintSystem::SolutionKind ConstraintSystem::simplifySubclassOfConstraint(
+                                 Type type,
+                                 Type classType,
+                                 ConstraintLocatorBuilder locator,
+                                 TypeMatchOptions flags) {
+  if (!classType->getClassOrBoundGenericClass())
+    return SolutionKind::Error;
+
+  // Dig out the fixed type to which this type refers.
+  type = getFixedTypeRecursive(type, flags, /*wantRValue=*/true);
+  if (shouldAttemptFixes() && type->isPlaceholder()) {
+    // If the type associated with this subclass check is a "hole" in the
+    // constraint system, let's consider this check a success without recording
+    // a fix, because it's just a consequence of the other failure, e.g.
+    //
+    // func foo<T: NSObject>(_: T) {}
+    // foo(Foo.bar) <- if `Foo` doesn't have `bar` there is
+    //                 no reason to complain the subclass.
+    return SolutionKind::Solved;
+  }
+
+  auto formUnsolved = [&](bool activate = false) {
+    // If we're supposed to generate constraints, do so.
+    if (flags.contains(TMF_GenerateConstraints)) {
+      auto *conformance = Constraint::create(
+          *this, ConstraintKind::SubclassOf, type, classType,
+          getConstraintLocator(locator));
+
+      addUnsolvedConstraint(conformance);
+      if (activate)
+        activateConstraint(conformance);
+
+      return SolutionKind::Solved;
+    }
+
+    return SolutionKind::Unsolved;
+  };
+
+  // If we hit a type variable without a fixed type, we can't
+  // solve this yet.
+  if (type->isTypeVariableOrMember())
+    return formUnsolved();
+
+  // SubclassOf constraints are generated when opening a generic
+  // signature with a RequirementKind::Superclass requirement, so
+  // we must handle pack types on the left by splitting up into
+  // smaller constraints.
+  if (auto *packType = type->getAs<PackType>()) {
+    for (unsigned i = 0, e = packType->getNumElements(); i < e; ++i) {
+      addConstraint(ConstraintKind::SubclassOf, packType->getElementType(i),
+                    classType, locator.withPathElement(LocatorPathElt::PackElement(i)));
+    }
+
+    return SolutionKind::Solved;
+  }
+
+  // A class-constrained existential like 'C & P' does not satisfy an
+  // AnyObject requirement, if 'P' is not self-conforming.
+  //
+  // While matchSuperclassTypes() will still match here because 'C & P'
+  // satisfies a Subtype constraint with 'C', 'C & P' cannot satisfy a
+  // superclass requirement in a generic signature, so rule that out here.
+  if (type->satisfiesClassConstraint()) {
+    // If we have an exact match of class declarations, ensure the
+    // generic arguments match.
+    if (type->getClassOrBoundGenericClass() ==
+        classType->getClassOrBoundGenericClass()) {
+      auto result = matchTypes(type, classType, ConstraintKind::Bind,
+                               flags, locator);
+      if (!result.isFailure())
+        return SolutionKind::Solved;
+
+    // Otherwise, ensure the left hand side is a proper subclass of the
+    // right hand side.
+    } else {
+      auto result = matchSuperclassTypes(type, classType, flags, locator);
+      if (!result.isFailure())
+        return SolutionKind::Solved;
+    }
+  }
+
+  // Record a fix if we didn't match one of the two cases above.
+  if (shouldAttemptFixes()) {
+    if (auto *fix = fixRequirementFailure(*this, type, classType, locator)) {
+      if (recordFix(fix))
+        return SolutionKind::Error;
+      return SolutionKind::Solved;
+    }
+  }
+
+  return SolutionKind::Error;
+}
+
 ConstraintSystem::SolutionKind ConstraintSystem::simplifyConformsToConstraint(
                                  Type type,
                                  Type protocol,
@@ -7375,6 +7472,21 @@ ConstraintSystem::SolutionKind ConstraintSystem::simplifyConformsToConstraint(
   if (type->isTypeVariableOrMember())
     return formUnsolved();
 
+  // ConformsTo constraints are generated when opening a generic
+  // signature with a RequirementKind::Conformance requirement, so
+  // we must handle pack types on the left by splitting up into
+  // smaller constraints.
+  if (auto *packType = type->getAs<PackType>()) {
+    for (unsigned i = 0, e = packType->getNumElements(); i < e; ++i) {
+      addConstraint(ConstraintKind::ConformsTo, packType->getElementType(i),
+                    protocol->getDeclaredInterfaceType(),
+                    locator.withPathElement(LocatorPathElt::PackElement(i)));
+    }
+
+    return SolutionKind::Solved;
+  }
+
+
   auto *loc = getConstraintLocator(locator);
 
   /// Record the given conformance as the result, adding any conditional
@@ -13551,6 +13663,9 @@ ConstraintSystem::addConstraintImpl(ConstraintKind kind, Type first,
     return simplifyOpenedExistentialOfConstraint(first, second,
                                                  subflags, locator);
 
+  case ConstraintKind::SubclassOf:
+    return simplifySubclassOfConstraint(first, second, locator, subflags);
+
   case ConstraintKind::ConformsTo:
   case ConstraintKind::LiteralConformsTo:
   case ConstraintKind::SelfObjectOfProtocol:
@@ -14029,6 +14144,13 @@ ConstraintSystem::simplifyConstraint(const Constraint &constraint) {
                     constraint.getOverloadUseDC());
     return SolutionKind::Solved;
 
+  case ConstraintKind::SubclassOf:
+    return simplifySubclassOfConstraint(
+             constraint.getFirstType(),
+             constraint.getSecondType(),
+             constraint.getLocator(),
+             /*flags*/ None);
+
   case ConstraintKind::ConformsTo:
   case ConstraintKind::LiteralConformsTo:
   case ConstraintKind::SelfObjectOfProtocol:
@@ -14049,7 +14171,7 @@ ConstraintSystem::simplifyConstraint(const Constraint &constraint) {
   case ConstraintKind::CheckedCast: {
     auto result = simplifyCheckedCastConstraint(constraint.getFirstType(),
                                                 constraint.getSecondType(),
-                                                None,
+                                                /*flags*/ None,
                                                 constraint.getLocator());
     // NOTE: simplifyCheckedCastConstraint() may return Unsolved, e.g. if the
     // subexpression's type is unresolved. Don't record the fix until we

lib/Sema/Constraint.cpp

@@ -64,6 +64,7 @@ Constraint::Constraint(ConstraintKind Kind, Type First, Type Second,
   case ConstraintKind::BridgingConversion:
   case ConstraintKind::ArgumentConversion:
   case ConstraintKind::OperatorArgumentConversion:
+  case ConstraintKind::SubclassOf:
   case ConstraintKind::ConformsTo:
   case ConstraintKind::LiteralConformsTo:
   case ConstraintKind::TransitivelyConformsTo:
@@ -138,6 +139,7 @@ Constraint::Constraint(ConstraintKind Kind, Type First, Type Second, Type Third,
   case ConstraintKind::BridgingConversion:
   case ConstraintKind::ArgumentConversion:
   case ConstraintKind::OperatorArgumentConversion:
+  case ConstraintKind::SubclassOf:
   case ConstraintKind::ConformsTo:
   case ConstraintKind::LiteralConformsTo:
   case ConstraintKind::TransitivelyConformsTo:
@@ -290,6 +292,7 @@ Constraint *Constraint::clone(ConstraintSystem &cs) const {
   case ConstraintKind::BridgingConversion:
   case ConstraintKind::ArgumentConversion:
   case ConstraintKind::OperatorArgumentConversion:
+  case ConstraintKind::SubclassOf:
   case ConstraintKind::ConformsTo:
   case ConstraintKind::LiteralConformsTo:
   case ConstraintKind::TransitivelyConformsTo:
@@ -438,6 +441,7 @@ void Constraint::print(llvm::raw_ostream &Out, SourceManager *sm, unsigned inden
   case ConstraintKind::ArgumentConversion: Out << " arg conv "; break;
   case ConstraintKind::OperatorArgumentConversion:
       Out << " operator arg conv "; break;
+  case ConstraintKind::SubclassOf: Out << " subclass of "; break;
   case ConstraintKind::ConformsTo: Out << " conforms to "; break;
   case ConstraintKind::LiteralConformsTo: Out << " literal conforms to "; break;
   case ConstraintKind::TransitivelyConformsTo: Out << " transitive conformance to "; break;
@@ -695,6 +699,7 @@ gatherReferencedTypeVars(Constraint *constraint,
   case ConstraintKind::OpenedExistentialOf:
   case ConstraintKind::OptionalObject:
   case ConstraintKind::Defaultable:
+  case ConstraintKind::SubclassOf:
   case ConstraintKind::ConformsTo:
   case ConstraintKind::LiteralConformsTo:
   case ConstraintKind::TransitivelyConformsTo: