[Sema] Always look through optionals for unresolved member lookup

Author: Jumhyn

include/swift/Sema/ConstraintSystem.h

@@ -785,6 +785,8 @@ enum ScoreKind {
   SK_ForwardTrailingClosure,
   /// A use of a disfavored overload.
   SK_DisfavoredOverload,
+  /// A member for an \c UnresolvedMemberExpr found via unwrapped optional base.
+  SK_UnresolvedMemberViaOptional,
   /// An implicit force of an implicitly unwrapped optional value.
   SK_ForceUnchecked,
   /// A user-defined conversion.

lib/Sema/CSRanking.cpp

@@ -52,6 +52,9 @@ static StringRef getScoreKindName(ScoreKind kind) {
   case SK_DisfavoredOverload:
     return "disfavored overload";
 
+  case SK_UnresolvedMemberViaOptional:
+    return "unwrapping optional at unresolved member base";
+
   case SK_ForceUnchecked:
     return "force of an implicitly unwrapped optional";
 

lib/Sema/CSSimplify.cpp

@@ -6777,13 +6777,12 @@ performMemberLookup(ConstraintKind constraintKind, DeclNameRef memberName,
   // through optional types.
   //
   // FIXME: Unify with the above code path.
-  if (result.ViableCandidates.empty() &&
-      baseObjTy->is<AnyMetatypeType>() &&
+  if (baseObjTy->is<AnyMetatypeType>() &&
       constraintKind == ConstraintKind::UnresolvedValueMember) {
     if (auto objectType = instanceTy->getOptionalObjectType()) {
       // If we don't have a wrapped type yet, we can't look through the optional
       // type.
-      if (objectType->getAs<TypeVariableType>()) {
+      if (objectType->getAs<TypeVariableType>() && result.ViableCandidates.empty()) {
         MemberLookupResult result;
         result.OverallResult = MemberLookupResult::Unsolved;
         return result;

lib/Sema/ConstraintSystem.cpp

@@ -2802,6 +2802,11 @@ void ConstraintSystem::resolveOverload(ConstraintLocator *locator,
       choice.getDecl()->getAttrs().hasAttribute<DisfavoredOverloadAttr>()) {
     increaseScore(SK_DisfavoredOverload);
   }
+
+  if (choice.getKind() == OverloadChoiceKind::DeclViaUnwrappedOptional &&
+      locator->isLastElement<LocatorPathElt::UnresolvedMember>()) {
+    increaseScore(SK_UnresolvedMemberViaOptional);
+  }
 }
 
 Type ConstraintSystem::simplifyTypeImpl(Type type,

test/expr/delayed-ident/optional_overload.swift

@@ -0,0 +1,47 @@
+// RUN: %target-typecheck-verify-swift -dump-ast > %t.dump
+// RUN: %FileCheck %s < %t.dump
+
+// SR-13815
+extension Optional {
+    func sr13815() -> SR13815? { SR13815() }
+    static func sr13815_2() -> SR13815? { SR13815() }
+    static func sr13815_3() -> SR13815? { SR13815() }
+    static var sr13815_wrongType: Int { 0 }
+    static var sr13815_overload: SR13815 { SR13815() }
+    init(overloaded: Void) { self = nil }
+}
+
+struct SR13815 {
+    static var sr13815: SR13815? = SR13815()
+    static var sr13815_2: SR13815? = SR13815()
+    static var sr13815_wrongType: SR13815? { SR13815() }
+    static var p_SR13815: SR13815? { SR13815() }
+    static func sr13815_3() -> SR13815? { SR13815() }
+    static var sr13815_overload: SR13815? { SR13815() }
+    init(overloaded: Void) {}
+    init?(failable: Void) {}
+    init() {}
+}
+
+protocol P_SR13815 {}
+extension Optional: P_SR13815 where Wrapped: Equatable {
+    static func p_SR13815() {}
+}
+
+let _: SR13815? = .sr13815
+let _: SR13815? = .sr13815_wrongType
+let _: SR13815? = .init()
+let _: SR13815? = .sr13815() // expected-error {{instance member 'sr13815' cannot be used on type 'SR13815?'}}
+let _: SR13815? = .sr13815_2()
+let _: SR13815? = .init(SR13815())
+let _: SR13815? = .init(overloaded: ())
+// If members exist on Optional and Wrapped, always choose the one on optional
+// CHECK: declref_expr {{.*}} location={{.*}}optional_overload.swift:37
+// CHECK-SAME: decl=optional_overload.(file).Optional extension.init(overloaded:)
+let _: SR13815? = .sr13815_overload
+// Should choose the overload from Optional even if the Wrapped overload would otherwise have a better score
+// CHECK: member_ref_expr {{.*}} location={{.*}}optional_overload.swift:41
+// CHECK-SAME: decl=optional_overload.(file).Optional extension.sr13815_overload
+let _: SR13815? = .init(failable: ())
+let _: SR13815? = .sr13815_3()
+let _: SR13815? = .p_SR13815