[ConstraintSystem] Introduce new LValueObject constraint

Author: xedin

include/swift/Sema/Constraint.h

@@ -221,6 +221,8 @@ enum class ConstraintKind : char {
   /// The first type is a tuple containing a single unlabeled element that is a
   /// pack expansion. The second type is its pattern type.
   MaterializePackExpansion,
+  /// The first type is a l-value type whose object type is the second type.
+  LValueObject,
 };
 
 /// Classification of the different kinds of constraints.
@@ -691,6 +693,7 @@ class Constraint final : public llvm::ilist_node<Constraint>,
     case ConstraintKind::PackElementOf:
     case ConstraintKind::SameShape:
     case ConstraintKind::MaterializePackExpansion:
+    case ConstraintKind::LValueObject:
       return ConstraintClassification::Relational;
 
     case ConstraintKind::ValueMember:

include/swift/Sema/ConstraintSystem.h

@@ -5239,6 +5239,12 @@ class ConstraintSystem {
                                              TypeMatchOptions flags,
                                              ConstraintLocatorBuilder locator);
 
+  /// Extract the object type of the l-value type (type1) and bind it to
+  /// to type2.
+  SolutionKind simplifyLValueObjectConstraint(Type type1, Type type2,
+                                              TypeMatchOptions flags,
+                                              ConstraintLocatorBuilder locator);
+
 public: // FIXME: Public for use by static functions.
   /// Simplify a conversion constraint with a fix applied to it.
   SolutionKind simplifyFixConstraint(ConstraintFix *fix, Type type1, Type type2,

lib/Sema/CSBindings.cpp

@@ -1797,6 +1797,11 @@ void PotentialBindings::infer(Constraint *constraint) {
     // Constraints from which we can't do anything.
     break;
 
+  case ConstraintKind::LValueObject: {
+    DelayedBy.push_back(constraint);
+    break;
+  }
+
   // For now let's avoid inferring protocol requirements from
   // this constraint, but in the future we could do that to
   // to filter bindings.

lib/Sema/CSSimplify.cpp

@@ -2313,6 +2313,7 @@ ConstraintSystem::matchTupleTypes(TupleType *tuple1, TupleType *tuple2,
   case ConstraintKind::ExplicitGenericArguments:
   case ConstraintKind::SameShape:
   case ConstraintKind::MaterializePackExpansion:
+  case ConstraintKind::LValueObject:
     llvm_unreachable("Bad constraint kind in matchTupleTypes()");
   }
 
@@ -2673,6 +2674,7 @@ static bool matchFunctionRepresentations(FunctionType::ExtInfo einfo1,
   case ConstraintKind::ExplicitGenericArguments:
   case ConstraintKind::SameShape:
   case ConstraintKind::MaterializePackExpansion:
+  case ConstraintKind::LValueObject:
     return true;
   }
 
@@ -3318,6 +3320,7 @@ ConstraintSystem::matchFunctionTypes(FunctionType *func1, FunctionType *func2,
   case ConstraintKind::ExplicitGenericArguments:
   case ConstraintKind::SameShape:
   case ConstraintKind::MaterializePackExpansion:
+  case ConstraintKind::LValueObject:
     llvm_unreachable("Not a relational constraint");
   }
 
@@ -7179,6 +7182,7 @@ ConstraintSystem::matchTypes(Type type1, Type type2, ConstraintKind kind,
     case ConstraintKind::ExplicitGenericArguments:
     case ConstraintKind::SameShape:
     case ConstraintKind::MaterializePackExpansion:
+    case ConstraintKind::LValueObject:
       llvm_unreachable("Not a relational constraint");
     }
   }
@@ -14147,6 +14151,13 @@ ConstraintSystem::simplifyExplicitGenericArgumentsConstraint(
   return SolutionKind::Solved;
 }
 
+ConstraintSystem::SolutionKind 
+ConstraintSystem::simplifyLValueObjectConstraint(
+    Type type1, Type type2, TypeMatchOptions flags,
+    ConstraintLocatorBuilder locator) {
+  return SolutionKind::Error;
+}
+
 static llvm::PointerIntPair<Type, 3, unsigned>
 getBaseTypeForPointer(TypeBase *type) {
   unsigned unwrapCount = 0;
@@ -15614,6 +15625,9 @@ ConstraintSystem::addConstraintImpl(ConstraintKind kind, Type first,
     return simplifyMaterializePackExpansionConstraint(first, second, subflags,
                                                       locator);
 
+  case ConstraintKind::LValueObject:
+    return simplifyLValueObjectConstraint(first, second, subflags, locator);
+
   case ConstraintKind::ValueMember:
   case ConstraintKind::UnresolvedValueMember:
   case ConstraintKind::ValueWitness:
@@ -16209,6 +16223,11 @@ ConstraintSystem::simplifyConstraint(const Constraint &constraint) {
     return simplifyMaterializePackExpansionConstraint(
         constraint.getFirstType(), constraint.getSecondType(),
         /*flags*/ std::nullopt, constraint.getLocator());
+
+  case ConstraintKind::LValueObject:
+    return simplifyLValueObjectConstraint(
+        constraint.getFirstType(), constraint.getSecondType(),
+        /*flags*/ std::nullopt, constraint.getLocator());
   }
 
   llvm_unreachable("Unhandled ConstraintKind in switch.");

lib/Sema/Constraint.cpp

@@ -85,6 +85,7 @@ Constraint::Constraint(ConstraintKind Kind, Type First, Type Second,
   case ConstraintKind::ExplicitGenericArguments:
   case ConstraintKind::SameShape:
   case ConstraintKind::MaterializePackExpansion:
+  case ConstraintKind::LValueObject:
     assert(!First.isNull());
     assert(!Second.isNull());
     break;
@@ -176,6 +177,7 @@ Constraint::Constraint(ConstraintKind Kind, Type First, Type Second, Type Third,
   case ConstraintKind::ExplicitGenericArguments:
   case ConstraintKind::SameShape:
   case ConstraintKind::MaterializePackExpansion:
+  case ConstraintKind::LValueObject:
     llvm_unreachable("Wrong constructor");
 
   case ConstraintKind::KeyPath:
@@ -326,6 +328,7 @@ Constraint *Constraint::clone(ConstraintSystem &cs) const {
   case ConstraintKind::ExplicitGenericArguments:
   case ConstraintKind::SameShape:
   case ConstraintKind::MaterializePackExpansion:
+  case ConstraintKind::LValueObject:
     return create(cs, getKind(), getFirstType(), getSecondType(), getLocator());
 
   case ConstraintKind::ApplicableFunction:
@@ -590,6 +593,10 @@ void Constraint::print(llvm::raw_ostream &Out, SourceManager *sm,
     Out << " materialize pack expansion ";
     break;
 
+  case ConstraintKind::LValueObject:
+    Out << " l-value object type ";
+    break;
+
   case ConstraintKind::Disjunction:
     llvm_unreachable("disjunction handled above");
   case ConstraintKind::Conjunction:
@@ -760,6 +767,7 @@ gatherReferencedTypeVars(Constraint *constraint,
   case ConstraintKind::ExplicitGenericArguments:
   case ConstraintKind::SameShape:
   case ConstraintKind::MaterializePackExpansion:
+  case ConstraintKind::LValueObject:
     constraint->getFirstType()->getTypeVariables(typeVars);
     constraint->getSecondType()->getTypeVariables(typeVars);
     break;