Revert "[CSBindings] Don't favor application result types before application happens"

This reverts commit bc949c3.

Author: xedin

include/swift/Sema/ConstraintSystem.h

@@ -486,10 +486,6 @@ class TypeVariableType::Implementation {
   /// Determine whether this type variable represents a subscript result type.
   bool isSubscriptResultType() const;
 
-  /// Determine whether this type variable represents a result type of an
-  /// application i.e. a call, an operator, or a subscript.
-  bool isApplicationResultType() const;
-
   /// Determine whether this type variable represents an opened
   /// type parameter pack.
   bool isParameterPack() const;

lib/Sema/CSBindings.cpp

@@ -1281,16 +1281,9 @@ bool BindingSet::favoredOverDisjunction(Constraint *disjunction) const {
 
         return !hasConversions(binding.BindingType);
       })) {
-    bool isApplicationResultType = TypeVar->getImpl().isApplicationResultType();
-    if (llvm::none_of(Info.DelayedBy, [&isApplicationResultType](
-                                          const Constraint *constraint) {
-          // Let's not attempt to bind result type before application
-          // happens. For example because it could be discardable or
-          // l-value (subscript applications).
-          if (isApplicationResultType &&
-              constraint->getKind() == ConstraintKind::ApplicableFunction)
-            return true;
-
+    // Result type of subscript could be l-value so we can't bind it early.
+    if (!TypeVar->getImpl().isSubscriptResultType() &&
+        llvm::none_of(Info.DelayedBy, [](const Constraint *constraint) {
           return constraint->getKind() == ConstraintKind::Disjunction ||
                  constraint->getKind() == ConstraintKind::ValueMember;
         }))

lib/Sema/TypeCheckConstraints.cpp

@@ -175,16 +175,6 @@ bool TypeVariableType::Implementation::isSubscriptResultType() const {
              KeyPathExpr::Component::Kind::UnresolvedSubscript;
 }
 
-bool TypeVariableType::Implementation::isApplicationResultType() const {
-  if (!(locator && locator->getAnchor()))
-    return false;
-
-  if (!locator->isLastElement<LocatorPathElt::FunctionResult>())
-    return false;
-
-  return isExpr<ApplyExpr>(locator->getAnchor()) || isSubscriptResultType();
-}
-
 bool TypeVariableType::Implementation::isParameterPack() const {
   return locator
       && locator->isForGenericParameter()

test/Constraints/async.swift

@@ -180,20 +180,3 @@ struct OverloadInImplicitAsyncClosure {
 
   init(int: Int) throws { }
 }
-
-@available(SwiftStdlib 5.5, *)
-func test(_: Int) async throws {}
-
-@discardableResult
-@available(SwiftStdlib 5.5, *)
-func test(_: Int) -> String { "" }
-
-@available(SwiftStdlib 5.5, *)
-func compute(_: @escaping () -> Void) {}
-
-@available(SwiftStdlib 5.5, *)
-func test_sync_in_closure_context() {
-  compute {
-    test(42) // Ok (select sync overloads and discards the result)
-  }
-}