Sema: Account for existential member access limitations in doesStorageProduceLValue

Author: AnthonyLatsis

lib/Sema/CSSimplify.cpp

@@ -9876,8 +9876,7 @@ performMemberLookup(ConstraintKind constraintKind, DeclNameRef memberName,
     const auto isUnsupportedExistentialMemberAccess = [&] {
       // We may not be able to derive a well defined type for an existential
       // member access if the member's signature references 'Self'.
-      if (instanceTy->isExistentialType() &&
-          decl->getDeclContext()->getSelfProtocolDecl()) {
+      if (instanceTy->isExistentialType()) {
         switch (isMemberAvailableOnExistential(instanceTy, decl)) {
         case ExistentialMemberAccessLimitation::Unsupported:
         // TODO: Write-only accesses are not supported yet.

lib/Sema/OpenedExistentials.cpp

@@ -515,13 +515,14 @@ static bool doesMemberHaveUnfulfillableConstraintsWithExistentialBase(
 
 ExistentialMemberAccessLimitation
 swift::isMemberAvailableOnExistential(Type baseTy, const ValueDecl *member) {
+  auto *dc = member->getDeclContext();
+  if (!dc->getSelfProtocolDecl()) {
+    return ExistentialMemberAccessLimitation::None;
+  }
 
   auto &ctx = member->getASTContext();
   auto existentialSig = ctx.getOpenedExistentialSignature(baseTy);
 
-  auto *dc = member->getDeclContext();
-  ASSERT(dc->getSelfProtocolDecl());
-
   auto origParam = dc->getSelfInterfaceType()->castTo<GenericTypeParamType>();
   auto openedParam = existentialSig.SelfType->castTo<GenericTypeParamType>();
 

lib/Sema/TypeOfReference.cpp

@@ -505,13 +505,33 @@ static bool doesStorageProduceLValue(
   if (!storage->isSetterAccessibleFrom(useDC))
     return false;
 
-  //  if (baseType) {
-  //    isMemberAvailableOnExistential(baseType, storage)
-  //  }
-  // If there is no base, or the base is an lvalue, then a reference
-  // produces an lvalue.
-  if (!baseType || baseType->is<LValueType>())
+  // This path handles storage that is mutable in the given context.
+
+  if (!baseType) {
     return true;
+  }
+
+  {
+    const auto rValueInstanceTy =
+        baseType->getRValueType()->getMetatypeInstanceType();
+    if (rValueInstanceTy->isExistentialType()) {
+      switch (isMemberAvailableOnExistential(rValueInstanceTy, storage)) {
+      case ExistentialMemberAccessLimitation::Unsupported:
+      case ExistentialMemberAccessLimitation::ReadOnly:
+        // Never an lvalue because the current type system cannot represent the
+        // setter's type out of context.
+        return false;
+
+      case ExistentialMemberAccessLimitation::WriteOnly:
+      case ExistentialMemberAccessLimitation::None:
+        break;
+      }
+    }
+  }
+
+  if (baseType->is<LValueType>()) {
+    return true;
+  }
 
   // The base is an rvalue type. The only way an accessor can
   // produce an lvalue is if we have a property where both the

test/Sema/open_existential_lvalue.swift

@@ -1,34 +1,15 @@
 // RUN: %target-typecheck-verify-swift
 
 // rdar://121214563
+// https://github.com/swiftlang/swift/issues/60619
 // REQUIRES: rdar121214563
 
 protocol Q {}
 
-protocol P {
-  associatedtype T: Q
-  var member: T { get set }
-  var otherMember: any Q { get set }
-  subscript(_: Int) -> T { get set }
-}
-
 func takesAny(x: any Q) {}
 func takesRValue(x: any Q) {}
 func takesInOut(x: inout any Q) {}
 
-func f(data: inout any P) {
-  takesAny(x: data.member)
-  takesAny(x: data[0])
-
-  takesRValue(x: data.member)
-  takesRValue(x: data[0])
-
-  takesInOut(x: &data.member) // expected-error {{cannot pass immutable value as inout argument: 'data' is immutable}}
-  takesInOut(x: &data[0]) // expected-error {{cannot pass immutable value as inout argument: 'data' is immutable}}
-
-  takesInOut(x: &data.otherMember) // okay
-}
-
 struct S {
   subscript<T: Q>(_ ct: T.Type) -> T {
     get { fatalError() }
@@ -41,28 +22,3 @@ func f(s: inout S, t: any Q.Type) -> (any Q) {
   takesRValue(x: s[t])
   takesInOut(x: &s[t]) // expected-error {{cannot pass immutable value as inout argument: 's' is immutable}}
 }
-
-// https://github.com/apple/swift/issues/62219
-do {
-  struct Action {
-      var intVar: Int
-      var strVar: String
-  }
-
-  protocol TestDelegate: AnyObject {
-      associatedtype ActionType
-      var actions: [ActionType] { get set }
-  }
-
-  class TestDelegateImpl: TestDelegate {
-      typealias ActionType = Action
-      var actions: [Action] = []
-  }
-
-  class TestViewController {
-      var testDelegate: (any TestDelegate)?
-      func testFunc() {
-          testDelegate?.actions.removeAll() // expected-error {{cannot use mutating member on immutable value: 'self' is immutable}}
-      }
-  }
-}