Parsing and type checking for the definition of isolated conformances

DougGregor · DougGregor · commit de29302cb759 · 2025-02-25T16:15:13.000-08:00
Allow a conformance to be "isolated", meaning that it stays in the same
isolation domain as the conforming type. Only allow this for
global-actor-isolated types.

When a conformance is isolated, a nonisolated requirement can be
witnessed by a declaration with the same global actor isolation as the
enclosing type.
diff --git a/include/swift/AST/ConformanceAttributes.h b/include/swift/AST/ConformanceAttributes.h
@@ -27,6 +27,9 @@ struct ConformanceAttributes {
 
   /// The location of the "unsafe" attribute if present.
   SourceLoc unsafeLoc;
+
+  /// The location of the "@isolated" attribute if present.
+  SourceLoc isolatedLoc;
   
   /// Merge other conformance attributes into this set.
   ConformanceAttributes &
@@ -37,6 +40,8 @@ struct ConformanceAttributes {
       preconcurrencyLoc = other.preconcurrencyLoc;
     if (other.unsafeLoc.isValid())
       unsafeLoc = other.unsafeLoc;
+    if (other.isolatedLoc.isValid())
+      isolatedLoc = other.isolatedLoc;
     return *this;
   }
 };
diff --git a/include/swift/AST/Decl.h b/include/swift/AST/Decl.h
@@ -1836,12 +1836,13 @@ struct InheritedEntry : public TypeLoc {
   bool isPreconcurrency() const {
     return getOptions().contains(ProtocolConformanceFlags::Preconcurrency);
   }
+  bool isIsolated() const {
+    return getOptions().contains(ProtocolConformanceFlags::Isolated);
+  }
 
   ExplicitSafety getExplicitSafety() const {
     if (getOptions().contains(ProtocolConformanceFlags::Unsafe))
       return ExplicitSafety::Unsafe;
-    if (getOptions().contains(ProtocolConformanceFlags::Safe))
-      return ExplicitSafety::Safe;
     return ExplicitSafety::Unspecified;
   }
 
@@ -1852,13 +1853,10 @@ struct InheritedEntry : public TypeLoc {
   }
 
   void setOption(ExplicitSafety safety) {
-    RawOptions = (getOptions() - ProtocolConformanceFlags::Unsafe
-                    - ProtocolConformanceFlags::Safe).toRaw();
+    RawOptions = (getOptions() - ProtocolConformanceFlags::Unsafe).toRaw();
     switch (safety) {
     case ExplicitSafety::Unspecified:
-      break;
     case ExplicitSafety::Safe:
-      RawOptions = (getOptions() | ProtocolConformanceFlags::Safe).toRaw();
       break;
     case ExplicitSafety::Unsafe:
       RawOptions = (getOptions() | ProtocolConformanceFlags::Unsafe).toRaw();
diff --git a/include/swift/AST/DiagnosticsSema.def b/include/swift/AST/DiagnosticsSema.def
@@ -2722,8 +2722,17 @@ WARNING(add_predates_concurrency_import,none,
 GROUPED_WARNING(remove_predates_concurrency_import,PreconcurrencyImport,
                 DefaultIgnore,
                 "'@preconcurrency' attribute on module %0 has no effect", (Identifier))
+NOTE(add_isolated_to_conformance,none,
+     "add 'isolated' to the %0 conformance to restrict it to %1 code",
+    (DeclName, ActorIsolation))
 NOTE(add_preconcurrency_to_conformance,none,
      "add '@preconcurrency' to the %0 conformance to defer isolation checking to run time", (DeclName))
+ERROR(isolated_conformance_not_global_actor_isolated,none,
+      "isolated conformance is only permitted on global-actor-isolated types",
+      ())
+ERROR(isolated_conformance_experimental_feature,none,
+      "isolated conformances require experimental feature "
+      " 'IsolatedConformances'", ())
 WARNING(remove_public_import,none,
         "public import of %0 was not used in public declarations or inlinable code",
         (Identifier))
diff --git a/include/swift/AST/ProtocolConformance.h b/include/swift/AST/ProtocolConformance.h
@@ -669,6 +669,11 @@ class NormalProtocolConformance : public RootProtocolConformance,
     return getOptions().contains(ProtocolConformanceFlags::Preconcurrency);
   }
 
+  /// Whether this is an isolated conformance.
+  bool isIsolated() const {
+    return getOptions().contains(ProtocolConformanceFlags::Isolated);
+  }
+
   /// Retrieve the location of `@preconcurrency`, if there is one and it is
   /// known.
   SourceLoc getPreconcurrencyLoc() const { return PreconcurrencyLoc; }
@@ -678,8 +683,6 @@ class NormalProtocolConformance : public RootProtocolConformance,
   ExplicitSafety getExplicitSafety() const {
     if (getOptions().contains(ProtocolConformanceFlags::Unsafe))
       return ExplicitSafety::Unsafe;
-    if (getOptions().contains(ProtocolConformanceFlags::Safe))
-      return ExplicitSafety::Safe;
     return ExplicitSafety::Unspecified;
   }
 
diff --git a/include/swift/AST/ProtocolConformanceOptions.h b/include/swift/AST/ProtocolConformanceOptions.h
@@ -34,8 +34,8 @@ enum class ProtocolConformanceFlags {
   /// @retroactive conformance
   Retroactive = 0x08,
 
-  /// @safe conformance
-  Safe = 0x10,
+  /// @isolated conformance
+  Isolated = 0x10,
 
   // Note: whenever you add a bit here, update
   // NumProtocolConformanceOptions below.
diff --git a/include/swift/Basic/Features.def b/include/swift/Basic/Features.def
@@ -450,11 +450,15 @@ SUPPRESSIBLE_EXPERIMENTAL_FEATURE(CustomAvailability, true)
 /// Be strict about the Sendable conformance of metatypes.
 EXPERIMENTAL_FEATURE(StrictSendableMetatypes, true)
 
+
 /// Allow public enumerations to be extensible by default
 /// regardless of whether the module they are declared in
 /// is resilient or not.
 EXPERIMENTAL_FEATURE(ExtensibleEnums, true)
 
+/// Allow isolated conformances.
+EXPERIMENTAL_FEATURE(IsolatedConformances, true)
+
 #undef EXPERIMENTAL_FEATURE_EXCLUDED_FROM_MODULE_INTERFACE
 #undef EXPERIMENTAL_FEATURE
 #undef UPCOMING_FEATURE
diff --git a/lib/AST/ConformanceLookupTable.h b/lib/AST/ConformanceLookupTable.h
@@ -154,6 +154,8 @@ class ConformanceLookupTable : public ASTAllocated<ConformanceLookupTable> {
         options |= ProtocolConformanceFlags::Preconcurrency;
       if (getUnsafeLoc().isValid())
         options |= ProtocolConformanceFlags::Unsafe;
+      if (getIsolatedLoc().isValid())
+        options |= ProtocolConformanceFlags::Isolated;
       return options;
     }
 
@@ -209,6 +211,11 @@ class ConformanceLookupTable : public ASTAllocated<ConformanceLookupTable> {
       return attributes.unsafeLoc;
     }
 
+    /// The location of the @isolated attribute, if any.
+    SourceLoc getIsolatedLoc() const {
+      return attributes.isolatedLoc;
+    }
+
     /// For an inherited conformance, retrieve the class declaration
     /// for the inheriting class.
     ClassDecl *getInheritingClass() const {
diff --git a/lib/AST/Decl.cpp b/lib/AST/Decl.cpp
@@ -1780,6 +1780,8 @@ InheritedEntry::InheritedEntry(const TypeLoc &typeLoc)
       setOption(ProtocolConformanceFlags::Unsafe);
     if (typeRepr->findAttrLoc(TypeAttrKind::Preconcurrency).isValid())
       setOption(ProtocolConformanceFlags::Preconcurrency);
+    if (typeRepr->findAttrLoc(TypeAttrKind::Isolated).isValid())
+      setOption(ProtocolConformanceFlags::Isolated);
   }
 }
 
diff --git a/lib/AST/FeatureSet.cpp b/lib/AST/FeatureSet.cpp
@@ -348,6 +348,11 @@ static bool usesFeatureABIAttribute(Decl *decl) {
   return getABIAttr(decl) != nullptr;
 }
 
+static bool usesFeatureIsolatedConformances(Decl *decl) { 
+  // FIXME: Check conformances associated with this decl?
+  return false;
+}
+
 UNINTERESTING_FEATURE(WarnUnsafe)
 UNINTERESTING_FEATURE(SafeInteropWrappers)
 UNINTERESTING_FEATURE(AssumeResilientCxxTypes)
diff --git a/lib/AST/NameLookup.cpp b/lib/AST/NameLookup.cpp
@@ -3144,6 +3144,12 @@ directReferencesForTypeRepr(Evaluator &evaluator, ASTContext &ctx,
                                        attributed->getTypeRepr(), dc, options);
   }
 
+  case TypeReprKind::Isolated: {
+    auto isolated = cast<IsolatedTypeRepr>(typeRepr);
+    return directReferencesForTypeRepr(evaluator, ctx,
+                                       isolated->getBase(), dc, options);
+  }
+
   case TypeReprKind::Composition: {
     auto composition = cast<CompositionTypeRepr>(typeRepr);
     for (auto component : composition->getTypes()) {
@@ -3217,7 +3223,6 @@ directReferencesForTypeRepr(Evaluator &evaluator, ASTContext &ctx,
   case TypeReprKind::Error:
   case TypeReprKind::Function:
   case TypeReprKind::Ownership:
-  case TypeReprKind::Isolated:
   case TypeReprKind::CompileTimeConst:
   case TypeReprKind::Metatype:
   case TypeReprKind::Protocol:
@@ -3933,6 +3938,21 @@ CustomAttrNominalRequest::evaluate(Evaluator &evaluator,
   return nullptr;
 }
 
+/// Find the location of 'isolated' within this type representation.
+static SourceLoc findIsolatedLoc(TypeRepr *typeRepr) {
+  do {
+    if (auto isolatedTypeRepr = dyn_cast<IsolatedTypeRepr>(typeRepr))
+      return isolatedTypeRepr->getLoc();
+
+    if (auto attrTypeRepr = dyn_cast<AttributedTypeRepr>(typeRepr)) {
+      typeRepr = attrTypeRepr->getTypeRepr();
+      continue;
+    }
+        
+    return SourceLoc();
+  } while (true);
+}
+
 /// Decompose the ith inheritance clause entry to a list of type declarations,
 /// inverses, and optional AnyObject member.
 void swift::getDirectlyInheritedNominalTypeDecls(
@@ -3971,6 +3991,9 @@ void swift::getDirectlyInheritedNominalTypeDecls(
     attributes.uncheckedLoc = typeRepr->findAttrLoc(TypeAttrKind::Unchecked);
     attributes.preconcurrencyLoc = typeRepr->findAttrLoc(TypeAttrKind::Preconcurrency);
     attributes.unsafeLoc = typeRepr->findAttrLoc(TypeAttrKind::Unsafe);
+    
+    // Look for an IsolatedTypeRepr.
+    attributes.isolatedLoc = findIsolatedLoc(typeRepr);
   }
 
   // Form the result.
diff --git a/lib/Parse/ParseType.cpp b/lib/Parse/ParseType.cpp
@@ -163,7 +163,9 @@ ParserResult<TypeRepr> Parser::parseTypeSimple(
     Diag<> MessageID, ParseTypeReason reason) {
   ParserResult<TypeRepr> ty;
 
-  if (isParameterSpecifier()) {
+  if (isParameterSpecifier() &&
+      !(!Context.LangOpts.hasFeature(Feature::IsolatedConformances) &&
+        Tok.isContextualKeyword("isolated"))) {
     // Type specifier should already be parsed before here. This only happens
     // for construct like 'P1 & inout P2'.
     diagnose(Tok.getLoc(), diag::attr_only_on_parameters, Tok.getRawText());
diff --git a/lib/Sema/TypeCheckProtocol.cpp b/lib/Sema/TypeCheckProtocol.cpp
@@ -2541,6 +2541,22 @@ checkIndividualConformance(NormalProtocolConformance *conformance) {
       ComplainLoc, diag::unchecked_conformance_not_special, ProtoType);
   }
 
+  // Complain if the conformance is isolated but the conforming type is
+  // not global-actor-isolated.
+  if (conformance->isIsolated()) {
+    auto enclosingNominal = DC->getSelfNominalTypeDecl();
+    if (!enclosingNominal ||
+        !getActorIsolation(enclosingNominal).isGlobalActor()) {
+      Context.Diags.diagnose(
+          ComplainLoc, diag::isolated_conformance_not_global_actor_isolated);
+    }
+    
+    if (!Context.LangOpts.hasFeature(Feature::IsolatedConformances)) {
+      Context.Diags.diagnose(
+          ComplainLoc, diag::isolated_conformance_experimental_feature);
+    }
+  }
+  
   bool allowImpliedConditionalConformance = false;
   if (Proto->isSpecificProtocol(KnownProtocolKind::Sendable)) {
     // In -swift-version 5 mode, a conditional conformance to a protocol can imply
@@ -3313,6 +3329,14 @@ static bool hasExplicitGlobalActorAttr(ValueDecl *decl) {
   return !globalActorAttr->first->isImplicit();
 }
 
+/// Determine whether the given actor isolation matches that of the enclosing
+/// type.
+static bool isolationMatchesEnclosingType(
+    ActorIsolation isolation, NominalTypeDecl *nominal) {
+  auto nominalIsolation = getActorIsolation(nominal);
+  return isolation == nominalIsolation;
+}
+
 std::optional<ActorIsolation>
 ConformanceChecker::checkActorIsolation(ValueDecl *requirement,
                                         ValueDecl *witness,
@@ -3342,7 +3366,8 @@ ConformanceChecker::checkActorIsolation(ValueDecl *requirement,
       Conformance->isPreconcurrency() &&
       !(requirementIsolation.isActorIsolated() ||
         requirement->getAttrs().hasAttribute<NonisolatedAttr>());
-
+  bool isIsolatedConformance = false;
+  
   switch (refResult) {
   case ActorReferenceResult::SameConcurrencyDomain:
     // If the witness has distributed-actor isolation, we have extra
@@ -3374,6 +3399,17 @@ ConformanceChecker::checkActorIsolation(ValueDecl *requirement,
 
     return std::nullopt;
   case ActorReferenceResult::EntersActor:
+    // If the conformance itself is isolated, and the witness isolation
+    // matches the enclosing type's isolation, treat this as being in the
+    // same concurrency domain.
+    if (Conformance->isIsolated() &&
+        refResult.isolation.isGlobalActor() &&
+        isolationMatchesEnclosingType(
+            refResult.isolation, DC->getSelfNominalTypeDecl())) {
+      sameConcurrencyDomain = true;
+      isIsolatedConformance = true;
+    }
+
     // Handled below.
     break;
   }
@@ -3446,7 +3482,12 @@ ConformanceChecker::checkActorIsolation(ValueDecl *requirement,
 
   // If we aren't missing anything or this is a witness to a `@preconcurrency`
   // conformance, do a Sendable check and move on.
-  if (!missingOptions || isPreconcurrency) {
+  if (!missingOptions || isPreconcurrency || isIsolatedConformance) {
+    // An isolated conformance won't ever leave the isolation domain in which
+    // it was created, so there is nothing to check.
+    if (isIsolatedConformance)
+      return std::nullopt;
+    
     // FIXME: Disable Sendable checking when the witness is an initializer
     // that is explicitly marked nonisolated.
     if (isa<ConstructorDecl>(witness) &&
@@ -3546,18 +3587,26 @@ ConformanceChecker::checkActorIsolation(ValueDecl *requirement,
       witness->diagnose(diag::note_add_nonisolated_to_decl, witness)
             .fixItInsert(witness->getAttributeInsertionLoc(true), "nonisolated ");
     }
-
+    
     // Another way to address the issue is to mark the conformance as
-    // "preconcurrency".
+    // "isolated" or "@preconcurrency".
     if (Conformance->getSourceKind() == ConformanceEntryKind::Explicit &&
-        !Conformance->isPreconcurrency() &&
-        !suggestedPreconcurrency &&
+        !Conformance->isIsolated() && !Conformance->isPreconcurrency() &&
+        !suggestedPreconcurrencyOrIsolated &&
         !requirementIsolation.isActorIsolated()) {
+      if (Context.LangOpts.hasFeature(Feature::IsolatedConformances)) {
+        Context.Diags.diagnose(Conformance->getProtocolNameLoc(),
+                               diag::add_isolated_to_conformance,
+                               Proto->getName(), refResult.isolation)
+            .fixItInsert(Conformance->getProtocolNameLoc(), "isolated ");
+      }
+
       Context.Diags.diagnose(Conformance->getProtocolNameLoc(),
                              diag::add_preconcurrency_to_conformance,
                              Proto->getName())
           .fixItInsert(Conformance->getProtocolNameLoc(), "@preconcurrency ");
-      suggestedPreconcurrency = true;
+      
+      suggestedPreconcurrencyOrIsolated = true;
     }
   }
 
diff --git a/lib/Sema/TypeCheckProtocol.h b/lib/Sema/TypeCheckProtocol.h
@@ -112,8 +112,8 @@ enum class ResolveWitnessResult {
 /// This helper class handles most of the details of checking whether a
 /// given type (\c Adoptee) conforms to a protocol (\c Proto).
 class ConformanceChecker : public WitnessChecker {
-  /// Whether we already suggested adding `@preconcurrency`.
-  bool suggestedPreconcurrency = false;
+  /// Whether we already suggested adding `@preconcurrency` or 'isolated'.
+  bool suggestedPreconcurrencyOrIsolated = false;
 
 public:
   NormalProtocolConformance *Conformance;
diff --git a/lib/Sema/TypeCheckType.cpp b/lib/Sema/TypeCheckType.cpp
@@ -5175,8 +5175,9 @@ NeverNullType
 TypeResolver::resolveIsolatedTypeRepr(IsolatedTypeRepr *repr,
                                       TypeResolutionOptions options) {
   // isolated is only value for non-EnumCaseDecl parameters.
-  if (!options.is(TypeResolverContext::FunctionInput) ||
-      options.hasBase(TypeResolverContext::EnumElementDecl)) {
+  if ((!options.is(TypeResolverContext::FunctionInput) ||
+       options.hasBase(TypeResolverContext::EnumElementDecl)) &&
+      !options.is(TypeResolverContext::Inherited)) {
     diagnoseInvalid(
         repr, repr->getSpecifierLoc(), diag::attr_only_on_parameters,
         "isolated");
@@ -5197,7 +5198,8 @@ TypeResolver::resolveIsolatedTypeRepr(IsolatedTypeRepr *repr,
     unwrappedType = dynamicSelfType->getSelfType();
   }
 
-  if (inStage(TypeResolutionStage::Interface)) {
+  if (inStage(TypeResolutionStage::Interface) &&
+      !options.is(TypeResolverContext::Inherited)) {
     if (auto *env = resolution.getGenericSignature().getGenericEnvironment())
       unwrappedType = env->mapTypeIntoContext(unwrappedType);
 
diff --git a/test/Concurrency/isolated_conformance.swift b/test/Concurrency/isolated_conformance.swift

Original file line number	Diff line number	Diff line change
`@@ -1780,6 +1780,8 @@ InheritedEntry::InheritedEntry(const TypeLoc &typeLoc)`
`1780`	`1780`	`setOption(ProtocolConformanceFlags::Unsafe);`
`1781`	`1781`	`if (typeRepr->findAttrLoc(TypeAttrKind::Preconcurrency).isValid())`
`1782`	`1782`	`setOption(ProtocolConformanceFlags::Preconcurrency);`
	`1783`	`+ if (typeRepr->findAttrLoc(TypeAttrKind::Isolated).isValid())`
	`1784`	`+ setOption(ProtocolConformanceFlags::Isolated);`
`1783`	`1785`	`}`
`1784`	`1786`	`}`
`1785`	`1787`