Split conformance isolation request to eliminate a reference cycle

Inference of conformance isolation needs to check whether all of the
witnesses are nonisolated. However, witness checking looks at
conformance isolation. To break this reference cycle, split the
conformance isolation request into two requests: a "raw" request that
looks at explicitly-specified isolation, and the existing one that
also performs inference. The existing one builds on the "raw" one, as
does a separate path for the conformance checker.

Fixes rdar://152461344.

Author: DougGregor

include/swift/AST/ProtocolConformance.h

@@ -132,6 +132,7 @@ class alignas(1 << DeclAlignInBits) ProtocolConformance
   Type ConformingType;
 
   friend class ConformanceIsolationRequest;
+  friend class RawConformanceIsolationRequest;
 
 protected:
   // clang-format off
@@ -141,11 +142,14 @@ class alignas(1 << DeclAlignInBits) ProtocolConformance
   union { uint64_t OpaqueBits;
 
     SWIFT_INLINE_BITFIELD_BASE(ProtocolConformance,
-                               1+
+                               1+1+
                                bitmax(NumProtocolConformanceKindBits, 8),
       /// The kind of protocol conformance.
       Kind : bitmax(NumProtocolConformanceKindBits, 8),
 
+      /// Whether the "raw" conformance isolation is "inferred", which applies to most conformances.
+      IsRawConformanceInferred : 1,
+
       /// Whether the computed actor isolation is nonisolated.
       IsComputedNonisolated : 1
     );
@@ -201,9 +205,18 @@ class alignas(1 << DeclAlignInBits) ProtocolConformance
   ProtocolConformance(ProtocolConformanceKind kind, Type conformingType)
     : ConformingType(conformingType) {
     Bits.ProtocolConformance.Kind = unsigned(kind);
+    Bits.ProtocolConformance.IsRawConformanceInferred = false;
     Bits.ProtocolConformance.IsComputedNonisolated = false;
   }
 
+  bool isRawConformanceInferred() const {
+    return Bits.ProtocolConformance.IsRawConformanceInferred;
+  }
+
+  void setRawConformanceInferred(bool value = true) {
+    Bits.ProtocolConformance.IsRawConformanceInferred = value;
+  }
+
   bool isComputedNonisolated() const {
     return Bits.ProtocolConformance.IsComputedNonisolated;
   }
@@ -258,6 +271,14 @@ class alignas(1 << DeclAlignInBits) ProtocolConformance
   /// Otherwise a new conformance will be created.
   ProtocolConformance *getCanonicalConformance();
 
+  /// Determine the "raw" actor isolation of this conformance, before applying any inference rules.
+  ///
+  /// Most clients should use `getIsolation()`, unless they are part of isolation inference
+  /// themselves (e.g., conformance checking).
+  ///
+  /// - Returns std::nullopt if the isolation will be inferred.
+  std::optional<ActorIsolation> getRawIsolation() const;
+
   /// Determine the actor isolation of this conformance.
   ActorIsolation getIsolation() const;
 
@@ -552,6 +573,7 @@ class NormalProtocolConformance : public RootProtocolConformance,
   friend class ValueWitnessRequest;
   friend class TypeWitnessRequest;
   friend class ConformanceIsolationRequest;
+  friend class RawConformanceIsolationRequest;
 
   /// The protocol being conformed to.
   ProtocolDecl *Protocol;

include/swift/AST/TypeCheckRequests.h

@@ -475,6 +475,28 @@ class ConformanceHasEffectRequest :
   bool isCached() const { return true; }
 };
 
+class RawConformanceIsolationRequest :
+    public SimpleRequest<RawConformanceIsolationRequest,
+                         std::optional<ActorIsolation>(ProtocolConformance *),
+                         RequestFlags::SeparatelyCached |
+                         RequestFlags::SplitCached> {
+public:
+  using SimpleRequest::SimpleRequest;
+
+private:
+  friend SimpleRequest;
+
+  // Evaluation.
+  std::optional<ActorIsolation>
+  evaluate(Evaluator &evaluator, ProtocolConformance *conformance) const;
+
+public:
+  // Separate caching.
+  bool isCached() const { return true; }
+  std::optional<std::optional<ActorIsolation>> getCachedResult() const;
+  void cacheResult(std::optional<ActorIsolation> result) const;
+};
+
 class ConformanceIsolationRequest :
     public SimpleRequest<ConformanceIsolationRequest,
                          ActorIsolation(ProtocolConformance *),

include/swift/AST/TypeCheckerTypeIDZone.def

@@ -406,6 +406,10 @@ SWIFT_REQUEST(TypeChecker, PolymorphicEffectRequirementsRequest,
 SWIFT_REQUEST(TypeChecker, ConformanceHasEffectRequest,
               bool(EffectKind, ProtocolConformanceRef),
               Cached, NoLocationInfo)
+SWIFT_REQUEST(TypeChecker, RawConformanceIsolationRequest,
+              std::optional<ActorIsolation>(ProtocolConformance *),
+              SeparatelyCached | SplitCached,
+              NoLocationInfo)
 SWIFT_REQUEST(TypeChecker, ConformanceIsolationRequest,
               ActorIsolation(ProtocolConformance *),
               SeparatelyCached | SplitCached,

lib/AST/TypeCheckRequests.cpp

@@ -1367,6 +1367,38 @@ void AssociatedConformanceRequest::cacheResult(
   conformance->setAssociatedConformance(index, assocConf);
 }
 
+//----------------------------------------------------------------------------//
+// RawConformanceIsolationRequest computation.
+//----------------------------------------------------------------------------//
+std::optional<std::optional<ActorIsolation>>
+RawConformanceIsolationRequest::getCachedResult() const {
+  // We only want to cache for global-actor-isolated conformances. For
+  // everything else, which is nearly every conformance, this request quickly
+  // returns "nonisolated" so there is no point in caching it.
+  auto conformance = std::get<0>(getStorage());
+
+  // Was actor isolation non-isolated?
+  if (conformance->isRawConformanceInferred())
+    return std::optional<ActorIsolation>();
+
+  ASTContext &ctx = conformance->getDeclContext()->getASTContext();
+  return ctx.evaluator.getCachedNonEmptyOutput(*this);
+}
+
+void RawConformanceIsolationRequest::cacheResult(
+    std::optional<ActorIsolation> result) const {
+  auto conformance = std::get<0>(getStorage());
+
+  // Common case: conformance is inferred, so there's no result.
+  if (!result) {
+    conformance->setRawConformanceInferred();
+    return;
+  }
+
+  ASTContext &ctx = conformance->getDeclContext()->getASTContext();
+  ctx.evaluator.cacheNonEmptyOutput(*this, std::move(result));
+}
+
 //----------------------------------------------------------------------------//
 // ConformanceIsolationRequest computation.
 //----------------------------------------------------------------------------//

lib/Sema/TypeCheckConcurrency.cpp

@@ -7978,6 +7978,14 @@ bool swift::diagnoseNonSendableFromDeinit(
       refLoc, diag::non_sendable_from_deinit, var);
 }
 
+std::optional<ActorIsolation> ProtocolConformance::getRawIsolation() const {
+  ASTContext &ctx = getDeclContext()->getASTContext();
+  auto conformance = const_cast<ProtocolConformance *>(this);
+  return evaluateOrDefault(
+      ctx.evaluator, RawConformanceIsolationRequest{conformance},
+      ActorIsolation());
+}
+
 ActorIsolation ProtocolConformance::getIsolation() const {
   ASTContext &ctx = getDeclContext()->getASTContext();
   auto conformance = const_cast<ProtocolConformance *>(this);
@@ -7986,16 +7994,18 @@ ActorIsolation ProtocolConformance::getIsolation() const {
       ActorIsolation());
 }
 
-ActorIsolation
-ConformanceIsolationRequest::evaluate(Evaluator &evaluator, ProtocolConformance *conformance) const {
+std::optional<ActorIsolation>
+RawConformanceIsolationRequest::evaluate(
+    Evaluator &evaluator, ProtocolConformance *conformance
+) const {
   // Only normal protocol conformances can be isolated.
   auto rootNormal =
       dyn_cast<NormalProtocolConformance>(conformance->getRootConformance());
   if (!rootNormal)
     return ActorIsolation::forNonisolated(false);
 
   if (conformance != rootNormal)
-    return rootNormal->getIsolation();
+    return rootNormal->getRawIsolation();
 
   // If the conformance is explicitly non-isolated, report that.
   if (rootNormal->getOptions().contains(ProtocolConformanceFlags::Nonisolated))
@@ -8045,9 +8055,15 @@ ConformanceIsolationRequest::evaluate(Evaluator &evaluator, ProtocolConformance
   if (rootNormal->isPreconcurrency())
     return ActorIsolation::forNonisolated(false);
 
+  return std::nullopt;
+}
 
-  // Isolation inference rules follow. If we aren't inferring isolated conformances,
-  // we're done.
+ActorIsolation swift::inferConformanceIsolation(
+    NormalProtocolConformance *conformance, bool hasKnownIsolatedWitness) {
+  auto dc = conformance->getDeclContext();
+  ASTContext &ctx = dc->getASTContext();
+
+  // If we aren't inferring isolated conformances, we're done.
   if (!ctx.LangOpts.hasFeature(Feature::InferIsolatedConformances))
     return ActorIsolation::forNonisolated(false);
 
@@ -8065,6 +8081,12 @@ ConformanceIsolationRequest::evaluate(Evaluator &evaluator, ProtocolConformance
 
   // If all of the value witnesses are nonisolated, then we should not infer
   // global actor isolation.
+  if (hasKnownIsolatedWitness) {
+    // The caller told us we have an isolated value witness, so infer
+    // the nominal isolation.
+    return nominalIsolation;
+  }
+
   bool anyIsolatedWitness = false;
   auto protocol = conformance->getProtocol();
   for (auto requirement : protocol->getMembers()) {
@@ -8093,6 +8115,29 @@ ConformanceIsolationRequest::evaluate(Evaluator &evaluator, ProtocolConformance
   return nominalIsolation;
 }
 
+ActorIsolation
+ConformanceIsolationRequest::evaluate(
+    Evaluator &evaluator, ProtocolConformance *conformance
+) const {
+  // If there is raw isolation, use that.
+  if (auto rawIsolation = conformance->getRawIsolation())
+    return *rawIsolation;
+
+  // Otherwise, we may infer isolation.
+
+  // Only normal protocol conformances can be isolated.
+  auto rootNormal =
+      dyn_cast<NormalProtocolConformance>(conformance->getRootConformance());
+  if (!rootNormal)
+    return ActorIsolation::forNonisolated(false);
+
+  if (conformance != rootNormal)
+    return rootNormal->getIsolation();
+
+  return inferConformanceIsolation(
+      rootNormal, /*hasKnownIsolatedWitness=*/false);
+}
+
 namespace {
   /// Identifies isolated conformances whose isolation differs from the
   /// context's isolation.

lib/Sema/TypeCheckConcurrency.h

@@ -778,6 +778,13 @@ bool checkIsolatedConformancesInContext(
     Type type, SourceLoc loc, const DeclContext *dc,
     HandleConformanceIsolationFn handleBad = doNotDiagnoseConformanceIsolation);
 
+/// For a protocol conformance that does not have a "raw" isolation, infer its isolation.
+///
+/// - hasKnownIsolatedWitness: indicates when it is known that there is an actor-isolated witness, meaning
+///   that this operation will not look at other witnesses to determine if they are all nonisolated.
+ActorIsolation inferConformanceIsolation(
+    NormalProtocolConformance *conformance, bool hasKnownIsolatedWitness);
+
 } // end namespace swift
 
 namespace llvm {

lib/Sema/TypeCheckProtocol.cpp

@@ -3353,6 +3353,16 @@ static bool hasExplicitGlobalActorAttr(ValueDecl *decl) {
   return !globalActorAttr->first->isImplicit();
 }
 
+/// Determine the isolation of a conformance with a known-isolated value witness.
+static ActorIsolation getConformanceIsolationForIsolatedWitness(
+    NormalProtocolConformance *conformance) {
+  if (auto rawIsolation = conformance->getRawIsolation())
+    return *rawIsolation;
+
+  return inferConformanceIsolation(
+      conformance, /*hasKnownIsolatedWitness=*/true);
+}
+
 std::optional<ActorIsolation>
 ConformanceChecker::checkActorIsolation(ValueDecl *requirement,
                                         ValueDecl *witness,
@@ -3416,7 +3426,8 @@ ConformanceChecker::checkActorIsolation(ValueDecl *requirement,
   case ActorReferenceResult::EntersActor: {
     // If the conformance itself is isolated to the same isolation domain as
     // the witness, treat this as being in the same concurrency domain.
-    auto conformanceIsolation = Conformance->getIsolation();
+    auto conformanceIsolation =
+        getConformanceIsolationForIsolatedWitness(Conformance);
     if (conformanceIsolation.isGlobalActor() &&
         refResult.isolation == conformanceIsolation) {
       sameConcurrencyDomain = true;

test/Concurrency/isolated_conformance_default_actor.swift

@@ -64,6 +64,11 @@ class OtherClass {
   var otherState: any Encodable.Type = CodableClass.self
 }
 
+struct Landmark: Codable {
+  var name: String
+  var foundingYear: Int
+}
+
 func acceptSendablePMeta<T: Sendable & P>(_: T.Type) { }
 func acceptSendableQMeta<T: Sendable & Q>(_: T.Type) { }