Remove @_distributedActorIndependent attribute entirely.

All its uses have been subsumed into `nonisolated`.

Author: DougGregor

docs/ReferenceGuides/UnderscoredAttributes.md

@@ -113,14 +113,6 @@ library), instead of at an arbitrary point in time.
 For more details, see the forum post on
 [dynamic method replacement](https://forums.swift.org/t/dynamic-method-replacement/16619).
 
-## `@_distributedActorIndependent`
-
-Marks a specific property of a distributed actor to be available even if the
-actor is remote.
-
-This only applies to two distributed actor properties `address` and `transport`.
-It cannot be safely declared on any properties defined by ordinary Swift code.
-
 ## `@_effects(effectname)`
 
 Tells the compiler that the implementation of the defined function is limited

include/swift/AST/Attr.def

@@ -658,12 +658,7 @@ CONTEXTUAL_SIMPLE_DECL_ATTR(distributed, DistributedActor,
   APIBreakingToAdd | APIBreakingToRemove,
   118)
 
-SIMPLE_DECL_ATTR(_distributedActorIndependent, DistributedActorIndependent,
-  OnFunc | OnVar |
-  DistributedOnly | UserInaccessible |
-  ABIStableToAdd | ABIStableToRemove |
-  APIBreakingToAdd | APIBreakingToRemove,
-  119)
+// 110 is unused
 
 SIMPLE_DECL_ATTR(_assemblyVision, EmitAssemblyVisionRemarks,
   OnFunc | UserInaccessible | NotSerialized | OnNominalType |

include/swift/AST/DiagnosticsSema.def

@@ -4616,9 +4616,6 @@ ERROR(distributed_actor_user_defined_special_property,none,
       "property %0 cannot be defined explicitly, as it conflicts with "
       "distributed actor synthesized stored property",
       (DeclName))
-ERROR(distributed_actor_independent_property_must_be_let,none,
-      "_distributedActorIndependent can be applied to properties, however they must be 'let'",
-      ())
 NOTE(distributed_actor_isolated_property,none,
       "distributed actor state is only available within the actor instance", // TODO: reword in terms of isolation
       ())

lib/Sema/DerivedConformanceDistributedActor.cpp

@@ -105,7 +105,7 @@ static ValueDecl *deriveDistributedActor_id(DerivedConformance &derived) {
   auto &C = derived.Context;
 
   // ```
-  // @_distributedActorIndependent
+  // nonisolated
   // let id: AnyActorIdentity
   // ```
   auto propertyType = C.getAnyActorIdentityDecl()->getDeclaredInterfaceType();
@@ -133,7 +133,7 @@ static ValueDecl *deriveDistributedActor_actorTransport(
   auto &C = derived.Context;
 
   // ```
-  // @_distributedActorIndependent
+  // nonisolated
   // let actorTransport: ActorTransport
   // ```
   // (no need for @actorIndependent because it is an immutable let)

lib/Sema/TypeCheckAttr.cpp

@@ -256,7 +256,6 @@ class AttributeChecker : public AttributeVisitor<AttributeChecker> {
 
   void visitActorAttr(ActorAttr *attr);
   void visitDistributedActorAttr(DistributedActorAttr *attr);
-  void visitDistributedActorIndependentAttr(DistributedActorIndependentAttr *attr);
   void visitGlobalActorAttr(GlobalActorAttr *attr);
   void visitAsyncAttr(AsyncAttr *attr);
   void visitMarkerAttr(MarkerAttr *attr);
@@ -5510,16 +5509,6 @@ void AttributeChecker::visitNonisolatedAttr(NonisolatedAttr *attr) {
   }
 }
 
-void AttributeChecker::visitDistributedActorIndependentAttr(DistributedActorIndependentAttr *attr) {
-  /// user-inaccessible _distributedActorIndependent can only be applied to let properties
-  if (auto var = dyn_cast<VarDecl>(D)) {
-    if (!var->isLet()) {
-      diagnoseAndRemoveAttr(attr, diag::distributed_actor_independent_property_must_be_let);
-      return;
-    }
-  }
-}
-
 void AttributeChecker::visitGlobalActorAttr(GlobalActorAttr *attr) {
   auto nominal = dyn_cast<NominalTypeDecl>(D);
   if (!nominal)

lib/Sema/TypeCheckConcurrency.cpp

@@ -2561,23 +2561,17 @@ static Optional<ActorIsolation> getIsolationFromAttributes(
   // If any of them are present, use that attribute.
   auto nonisolatedAttr = decl->getAttrs().getAttribute<NonisolatedAttr>();
   auto globalActorAttr = decl->getGlobalActorAttr();
-  auto distributedActorIndependentAttr =
-      decl->getAttrs().getAttribute<DistributedActorIndependentAttr>();
 
   // Remove implicit attributes if we only care about explicit ones.
   if (onlyExplicit) {
     if (nonisolatedAttr && nonisolatedAttr->isImplicit())
       nonisolatedAttr = nullptr;
     if (globalActorAttr && globalActorAttr->first->isImplicit())
       globalActorAttr = None;
-    if (distributedActorIndependentAttr &&
-        distributedActorIndependentAttr->isImplicit())
-      distributedActorIndependentAttr = nullptr;
   }
 
   unsigned numIsolationAttrs =
-    (nonisolatedAttr ? 1 : 0) + (globalActorAttr ? 1 : 0) +
-    (distributedActorIndependentAttr ? 1 : 0);
+    (nonisolatedAttr ? 1 : 0) + (globalActorAttr ? 1 : 0);
   if (numIsolationAttrs == 0)
     return None;
 
@@ -2594,32 +2588,20 @@ static Optional<ActorIsolation> getIsolationFromAttributes(
 
     if (globalActorAttr) {
       if (shouldDiagnose) {
-        if (globalActorAttr) {
-          const DeclAttribute *otherAttr =
-              nonisolatedAttr
-                ? static_cast<const DeclAttribute *>(nonisolatedAttr)
-                : distributedActorIndependentAttr;
-          decl->diagnose(
-              diag::actor_isolation_multiple_attr, decl->getDescriptiveKind(),
-              name, otherAttr->getAttrName(),
-              globalActorAttr->second->getName().str())
-            .highlight(otherAttr->getRangeWithAt())
-            .highlight(globalActorAttr->first->getRangeWithAt());
-        } else {
-          decl->diagnose(
-              diag::actor_isolation_multiple_attr, decl->getDescriptiveKind(),
-              name, nonisolatedAttr->getAttrName(),
-              distributedActorIndependentAttr->getAttrName())
-            .highlight(nonisolatedAttr->getRangeWithAt())
-            .highlight(distributedActorIndependentAttr->getRangeWithAt());
+        decl->diagnose(
+            diag::actor_isolation_multiple_attr, decl->getDescriptiveKind(),
+            name, nonisolatedAttr->getAttrName(),
+            globalActorAttr->second->getName().str())
+          .highlight(nonisolatedAttr->getRangeWithAt())
+          .highlight(globalActorAttr->first->getRangeWithAt());
         }
       }
     }
   }
 
-  // If the declaration is explicitly marked 'nonisolated' or distributed
-  // actor-independent, report it as nonisolated.
-  if (nonisolatedAttr || distributedActorIndependentAttr) {
+  // If the declaration is explicitly marked 'nonisolated', report it as
+  // independent.
+  if (nonisolatedAttr) {
     return ActorIsolation::forIndependent();
   }
 

lib/Sema/TypeCheckDeclOverride.cpp

@@ -1542,7 +1542,6 @@ namespace  {
     UNINTERESTING_ATTR(OriginallyDefinedIn)
     UNINTERESTING_ATTR(Actor)
     UNINTERESTING_ATTR(DistributedActor)
-    UNINTERESTING_ATTR(DistributedActorIndependent)
     UNINTERESTING_ATTR(GlobalActor)
     UNINTERESTING_ATTR(Async)
     UNINTERESTING_ATTR(Sendable)

test/Distributed/distributed_actor_isolation.swift

@@ -134,7 +134,7 @@ func test_outside(
   _ = distributed.name // expected-error{{distributed actor-isolated property 'name' can only be referenced inside the distributed actor}}
   _ = distributed.mutable // expected-error{{distributed actor-isolated property 'mutable' can only be referenced inside the distributed actor}}
 
-  // ==== special properties (@_distributedActorIndependent)
+  // ==== special properties (nonisolated, implicitly replicated)
   // the distributed actor's special fields may always be referred to
   _ = distributed.id
   _ = distributed.actorTransport