[5.9][ConstraintSystem] Use fallback type constraint to default pack expansion

include/swift/Sema/Constraint.h

@@ -186,14 +186,12 @@ enum class ConstraintKind : char {
   /// constraint.
   OneWayBindParam,
   /// If there is no contextual info e.g. `_ = { 42 }` default first type
-  /// to a second type (inferred closure type). This is effectively a
-  /// `Defaultable` constraint which a couple of differences:
+  /// to a second type. This is effectively a `Defaultable` constraint
+  /// which one significant difference:
   ///
-  /// - References inferred closure type and all of the outer parameters
-  ///   referenced by closure body.
   /// - Handled specially by binding inference, specifically contributes
   ///   to the bindings only if there are no contextual types available.
-  DefaultClosureType,
+  FallbackType,
   /// The first type represents a result of an unresolved member chain,
   /// and the second type is its base type. This constraint acts almost
   /// like `Equal` but also enforces following semantics:
@@ -701,7 +699,7 @@ class Constraint final : public llvm::ilist_node<Constraint>,
     case ConstraintKind::OptionalObject:
     case ConstraintKind::OneWayEqual:
     case ConstraintKind::OneWayBindParam:
-    case ConstraintKind::DefaultClosureType:
+    case ConstraintKind::FallbackType:
     case ConstraintKind::UnresolvedMemberChainBase:
     case ConstraintKind::PackElementOf:
     case ConstraintKind::SameShape:

include/swift/Sema/ConstraintSystem.h

@@ -4847,11 +4847,12 @@ class ConstraintSystem {
                                              TypeMatchOptions flags,
                                              ConstraintLocatorBuilder locator);
 
-  /// Attempt to simplify the given defaultable closure type constraint.
-  SolutionKind simplifyDefaultClosureTypeConstraint(
-      Type closureType, Type inferredType,
-      ArrayRef<TypeVariableType *> referencedOuterParameters,
-      TypeMatchOptions flags, ConstraintLocatorBuilder locator);
+  /// Attempt to simplify the given fallback type constraint.
+  SolutionKind
+  simplifyFallbackTypeConstraint(Type defaultableType, Type fallbackType,
+                                 ArrayRef<TypeVariableType *> referencedVars,
+                                 TypeMatchOptions flags,
+                                 ConstraintLocatorBuilder locator);
 
   /// Attempt to simplify a property wrapper constraint.
   SolutionKind simplifyPropertyWrapperConstraint(Type wrapperType, Type wrappedValueType,

lib/Sema/CSBindings.cpp

@@ -452,7 +452,7 @@ void BindingSet::inferTransitiveBindings(
 
     // Infer transitive defaults.
     for (const auto &def : bindings.Defaults) {
-      if (def.getSecond()->getKind() == ConstraintKind::DefaultClosureType)
+      if (def.getSecond()->getKind() == ConstraintKind::FallbackType)
         continue;
 
       addDefault(def.second);
@@ -1510,7 +1510,7 @@ void PotentialBindings::infer(Constraint *constraint) {
   }
 
   case ConstraintKind::Defaultable:
-  case ConstraintKind::DefaultClosureType:
+  case ConstraintKind::FallbackType:
     // Do these in a separate pass.
     if (CS.getFixedTypeRecursive(constraint->getFirstType(), true)
             ->getAs<TypeVariableType>() == TypeVar) {
@@ -1634,7 +1634,7 @@ void PotentialBindings::retract(Constraint *constraint) {
     break;
 
   case ConstraintKind::Defaultable:
-  case ConstraintKind::DefaultClosureType: {
+  case ConstraintKind::FallbackType: {
     Defaults.erase(constraint);
     break;
   }
@@ -2075,11 +2075,10 @@ bool TypeVarBindingProducer::computeNext() {
   if (NumTries == 0) {
     // Add defaultable constraints (if any).
     for (auto *constraint : DelayedDefaults) {
-      if (constraint->getKind() == ConstraintKind::DefaultClosureType) {
-        // If there are no other possible bindings for this closure
-        // let's default it to the type inferred from its parameters/body,
-        // otherwise we should only attempt contextual types as a
-        // top-level closure type.
+      if (constraint->getKind() == ConstraintKind::FallbackType) {
+        // If there are no other possible bindings for this variable
+        // let's default it to the fallback type, otherwise we should
+        // only attempt contextual types.
         if (!ExploredTypes.empty())
           continue;
       }

lib/Sema/CSGen.cpp

@@ -2921,9 +2921,9 @@ namespace {
       SmallVector<TypeVariableType *, 4> referencedVars{
           collectVarRefs.varRefs.begin(), collectVarRefs.varRefs.end()};
 
-      CS.addUnsolvedConstraint(Constraint::create(
-          CS, ConstraintKind::DefaultClosureType, closureType, inferredType,
-          locator, referencedVars));
+      CS.addUnsolvedConstraint(
+          Constraint::create(CS, ConstraintKind::FallbackType, closureType,
+                             inferredType, locator, referencedVars));
 
       CS.setClosureType(closure, inferredType);
       return closureType;

lib/Sema/CSSimplify.cpp

@@ -2284,7 +2284,7 @@ ConstraintSystem::matchTupleTypes(TupleType *tuple1, TupleType *tuple2,
   case ConstraintKind::BridgingConversion:
   case ConstraintKind::OneWayEqual:
   case ConstraintKind::OneWayBindParam:
-  case ConstraintKind::DefaultClosureType:
+  case ConstraintKind::FallbackType:
   case ConstraintKind::UnresolvedMemberChainBase:
   case ConstraintKind::PropertyWrapper:
   case ConstraintKind::SyntacticElement:
@@ -2643,7 +2643,7 @@ static bool matchFunctionRepresentations(FunctionType::ExtInfo einfo1,
   case ConstraintKind::ValueWitness:
   case ConstraintKind::OneWayEqual:
   case ConstraintKind::OneWayBindParam:
-  case ConstraintKind::DefaultClosureType:
+  case ConstraintKind::FallbackType:
   case ConstraintKind::UnresolvedMemberChainBase:
   case ConstraintKind::PropertyWrapper:
   case ConstraintKind::SyntacticElement:
@@ -3161,7 +3161,7 @@ ConstraintSystem::matchFunctionTypes(FunctionType *func1, FunctionType *func2,
   case ConstraintKind::BridgingConversion:
   case ConstraintKind::OneWayEqual:
   case ConstraintKind::OneWayBindParam:
-  case ConstraintKind::DefaultClosureType:
+  case ConstraintKind::FallbackType:
   case ConstraintKind::UnresolvedMemberChainBase:
   case ConstraintKind::PropertyWrapper:
   case ConstraintKind::SyntacticElement:
@@ -6814,7 +6814,7 @@ ConstraintSystem::matchTypes(Type type1, Type type2, ConstraintKind kind,
     case ConstraintKind::ValueWitness:
     case ConstraintKind::OneWayEqual:
     case ConstraintKind::OneWayBindParam:
-    case ConstraintKind::DefaultClosureType:
+    case ConstraintKind::FallbackType:
     case ConstraintKind::UnresolvedMemberChainBase:
     case ConstraintKind::PropertyWrapper:
     case ConstraintKind::SyntacticElement:
@@ -10950,18 +10950,18 @@ ConstraintSystem::SolutionKind ConstraintSystem::simplifyDefaultableConstraint(
   return SolutionKind::Solved;
 }
 
-ConstraintSystem::SolutionKind
-ConstraintSystem::simplifyDefaultClosureTypeConstraint(
-    Type closureType, Type inferredType,
-    ArrayRef<TypeVariableType *> referencedOuterParameters,
-    TypeMatchOptions flags, ConstraintLocatorBuilder locator) {
-  closureType = getFixedTypeRecursive(closureType, flags, /*wantRValue=*/true);
+ConstraintSystem::SolutionKind ConstraintSystem::simplifyFallbackTypeConstraint(
+    Type defaultableType, Type fallbackType,
+    ArrayRef<TypeVariableType *> referencedVars, TypeMatchOptions flags,
+    ConstraintLocatorBuilder locator) {
+  defaultableType =
+      getFixedTypeRecursive(defaultableType, flags, /*wantRValue=*/true);
 
-  if (closureType->isTypeVariableOrMember()) {
+  if (defaultableType->isTypeVariableOrMember()) {
     if (flags.contains(TMF_GenerateConstraints)) {
       addUnsolvedConstraint(Constraint::create(
-          *this, ConstraintKind::DefaultClosureType, closureType, inferredType,
-          getConstraintLocator(locator), referencedOuterParameters));
+          *this, ConstraintKind::FallbackType, defaultableType, fallbackType,
+          getConstraintLocator(locator), referencedVars));
       return SolutionKind::Solved;
     }
 
@@ -15014,7 +15014,7 @@ ConstraintSystem::addConstraintImpl(ConstraintKind kind, Type first,
   case ConstraintKind::Conjunction:
   case ConstraintKind::KeyPath:
   case ConstraintKind::KeyPathApplication:
-  case ConstraintKind::DefaultClosureType:
+  case ConstraintKind::FallbackType:
   case ConstraintKind::SyntacticElement:
     llvm_unreachable("Use the correct addConstraint()");
   }
@@ -15546,12 +15546,12 @@ ConstraintSystem::simplifyConstraint(const Constraint &constraint) {
                                          /*flags*/ None,
                                          constraint.getLocator());
 
-  case ConstraintKind::DefaultClosureType:
-    return simplifyDefaultClosureTypeConstraint(constraint.getFirstType(),
-                                                constraint.getSecondType(),
-                                                constraint.getTypeVariables(),
-                                                /*flags*/ None,
-                                                constraint.getLocator());
+  case ConstraintKind::FallbackType:
+    return simplifyFallbackTypeConstraint(constraint.getFirstType(),
+                                          constraint.getSecondType(),
+                                          constraint.getTypeVariables(),
+                                          /*flags*/ None,
+                                          constraint.getLocator());
 
   case ConstraintKind::PropertyWrapper:
     return simplifyPropertyWrapperConstraint(constraint.getFirstType(),

lib/Sema/Constraint.cpp

@@ -99,7 +99,7 @@ Constraint::Constraint(ConstraintKind Kind, Type First, Type Second,
     llvm_unreachable("Wrong constructor for member constraint");
 
   case ConstraintKind::Defaultable:
-  case ConstraintKind::DefaultClosureType:
+  case ConstraintKind::FallbackType:
     assert(!First.isNull());
     assert(!Second.isNull());
     break;
@@ -164,7 +164,7 @@ Constraint::Constraint(ConstraintKind Kind, Type First, Type Second, Type Third,
   case ConstraintKind::Conjunction:
   case ConstraintKind::OneWayEqual:
   case ConstraintKind::OneWayBindParam:
-  case ConstraintKind::DefaultClosureType:
+  case ConstraintKind::FallbackType:
   case ConstraintKind::UnresolvedMemberChainBase:
   case ConstraintKind::PropertyWrapper:
   case ConstraintKind::SyntacticElement:
@@ -314,7 +314,7 @@ Constraint *Constraint::clone(ConstraintSystem &cs) const {
   case ConstraintKind::Defaultable:
   case ConstraintKind::OneWayEqual:
   case ConstraintKind::OneWayBindParam:
-  case ConstraintKind::DefaultClosureType:
+  case ConstraintKind::FallbackType:
   case ConstraintKind::UnresolvedMemberChainBase:
   case ConstraintKind::PropertyWrapper:
   case ConstraintKind::BindTupleOfFunctionParams:
@@ -470,8 +470,8 @@ void Constraint::print(llvm::raw_ostream &Out, SourceManager *sm,
   case ConstraintKind::OpenedExistentialOf: Out << " opened archetype of "; break;
   case ConstraintKind::OneWayEqual: Out << " one-way bind to "; break;
   case ConstraintKind::OneWayBindParam: Out << " one-way bind param to "; break;
-  case ConstraintKind::DefaultClosureType:
-    Out << " closure can default to ";
+  case ConstraintKind::FallbackType:
+    Out << " can fallback to ";
     break;
   case ConstraintKind::UnresolvedMemberChainBase:
     Out << " unresolved member chain base ";
@@ -742,7 +742,7 @@ gatherReferencedTypeVars(Constraint *constraint,
   case ConstraintKind::SelfObjectOfProtocol:
   case ConstraintKind::OneWayEqual:
   case ConstraintKind::OneWayBindParam:
-  case ConstraintKind::DefaultClosureType:
+  case ConstraintKind::FallbackType:
   case ConstraintKind::UnresolvedMemberChainBase:
   case ConstraintKind::PropertyWrapper:
   case ConstraintKind::BindTupleOfFunctionParams:

lib/Sema/ConstraintSystem.cpp

@@ -1031,7 +1031,7 @@ Type ConstraintSystem::openPackExpansionType(PackExpansionType *expansion,
   // This constraint is important to make sure that pack expansion always
   // has a binding and connect pack expansion var to any type variables
   // that appear in pattern and shape types.
-  addUnsolvedConstraint(Constraint::create(*this, ConstraintKind::Defaultable,
+  addUnsolvedConstraint(Constraint::create(*this, ConstraintKind::FallbackType,
                                            expansionVar, openedPackExpansion,
                                            expansionLoc));
 
@@ -7391,7 +7391,7 @@ bool TypeVarBindingProducer::requiresOptionalAdjustment(
 PotentialBinding
 TypeVarBindingProducer::getDefaultBinding(Constraint *constraint) const {
   assert(constraint->getKind() == ConstraintKind::Defaultable ||
-         constraint->getKind() == ConstraintKind::DefaultClosureType);
+         constraint->getKind() == ConstraintKind::FallbackType);
 
   auto type = constraint->getSecondType();
   Binding binding{type, BindingKind::Exact, constraint};

test/Constraints/pack-expansion-expressions.swift

@@ -560,3 +560,45 @@ func configure<T, each Element>(
   repeat item[keyPath: (each configuration).0] = (each configuration).1
   return item
 }
+
+// rdar://110819621 - generic parameter is bound before pack expansion type which result in inference failures
+func test_that_expansions_are_bound_early() {
+  struct Data {
+    let prop: Int?
+  }
+
+  struct Value<each T> {
+    init(_ body: (repeat each T) -> Bool) {}
+  }
+
+  func compute<Root, Value>(
+    root: Root,
+    keyPath: KeyPath<Root, Value>,
+    other: Value) -> Bool { true }
+
+  func test_keypath(v: Int) {
+    let _: Value<Data> = Value({
+        compute(
+          root: $0,
+          keyPath: \.prop,
+          other: v
+        )
+      }) // Ok
+
+    let _: Value = Value<Data>({
+        compute(
+          root: $0,
+          keyPath: \.prop,
+          other: v
+        )
+      }) // Ok
+  }
+
+  func equal<Value>(_: Value, _: Value) -> Bool {}
+
+  func test_equality(i: Int) {
+    let _: Value<Data> = Value({
+        equal($0.prop, i) // Ok
+      })
+  }
+}

unittests/Sema/ConstraintSimplificationTests.cpp

@@ -111,7 +111,7 @@ TEST_F(SemaTest, TestClosureInferenceFromOptionalContext) {
   auto *closureTy = cs.createTypeVariable(closureLoc, /*options=*/0);
 
   cs.addUnsolvedConstraint(Constraint::create(
-      cs, ConstraintKind::DefaultClosureType, closureTy, defaultTy,
+      cs, ConstraintKind::FallbackType, closureTy, defaultTy,
       cs.getConstraintLocator(closure), /*referencedVars=*/{}));
 
   auto contextualTy =