Move generic signature check for isolated conformances into GenericSignatureImpl

This is going to need a proper implementation in the requirement
machine. For the moment, provide a slightly-less-broken implementation
but leave a test case where we incorrectly accept racey code.

Author: DougGregor

include/swift/AST/GenericSignature.h

@@ -376,6 +376,19 @@ class alignas(1 << TypeAlignInBits) GenericSignatureImpl final
   /// the given protocol.
   bool requiresProtocol(Type type, ProtocolDecl *proto) const;
 
+  /// Determine whether a conformance requirement of the given type to the
+  /// given protocol prohibits the use of an isolated conformance.
+  ///
+  /// The use of an isolated conformance to satisfy a requirement T: P is
+  /// prohibited when T is a type parameter and T, or some type that can be
+  /// used to reach T, also conforms to Sendable or SendableMetatype. In that
+  /// case, the conforming type and the protocol (Sendable or SendableMetatype)
+  /// is returned.
+  ///
+  /// If there is no such requirement, returns std::nullopt.
+  std::optional<std::pair<Type, ProtocolDecl *>>
+  prohibitsIsolatedConformance(Type type) const;
+
   /// Determine whether the given dependent type is equal to a concrete type.
   bool isConcreteType(Type type) const;
 

lib/AST/GenericSignature.cpp

@@ -371,6 +371,44 @@ bool GenericSignatureImpl::requiresProtocol(Type type,
   return getRequirementMachine()->requiresProtocol(type, proto);
 }
 
+std::optional<std::pair<Type, ProtocolDecl *>>
+GenericSignatureImpl::prohibitsIsolatedConformance(Type type) const {
+  type = getReducedType(type);
+
+  if (!type->isTypeParameter())
+    return std::nullopt;
+
+  // An isolated conformance cannot be used in a context where the type
+  // parameter can escape the isolation domain in which the conformance
+  // was formed. To establish this, we look for Sendable or SendableMetatype
+  // requirements on the type parameter itself.
+  ASTContext &ctx = type->getASTContext();
+  auto sendableProto = ctx.getProtocol(KnownProtocolKind::Sendable);
+  auto sendableMetatypeProto =
+      ctx.getProtocol(KnownProtocolKind::SendableMetatype);
+
+  // Check for a conformance requirement to SendableMetatype, which is
+  // implied by Sendable.
+  if (sendableMetatypeProto && requiresProtocol(type, sendableMetatypeProto)) {
+    // Check for a conformance requirement to Sendable and return that if
+    // it exists, because it's more recognizable and specific.
+    if (sendableProto && requiresProtocol(type, sendableProto))
+      return std::make_pair(type, sendableProto);
+
+    return std::make_pair(type, sendableMetatypeProto);
+  }
+
+  // If this is a nested type, also check whether the parent type conforms to
+  // SendableMetatype, because one can derive this type from the parent type.
+  // FIXME: This is not a complete check, because there are other ways in which
+  // one might be able to derive this type. This needs to determine whether
+  // there is any path from a SendableMetatype-conforming type to this type.
+  if (auto depMemTy = type->getAs<DependentMemberType>())
+    return prohibitsIsolatedConformance(depMemTy->getBase());
+
+  return std::nullopt;
+}
+
 /// Determine whether the given dependent type is equal to a concrete type.
 bool GenericSignatureImpl::isConcreteType(Type type) const {
   assert(type->isTypeParameter() && "Expected a type parameter");

lib/Sema/TypeCheckGeneric.cpp

@@ -1064,17 +1064,19 @@ CheckGenericArgumentsResult TypeChecker::checkGenericArgumentsForDiagnostics(
       break;
     }
 
-    if (!isolatedConformances.empty()) {
+    if (!isolatedConformances.empty() && signature) {
       // Dig out the original type parameter for the requirement.
       // FIXME: req might not be the right pre-substituted requirement,
       // if this came from a conditional requirement.
-      if (auto failedProtocol =
-              typeParameterProhibitsIsolatedConformance(req.getFirstType(),
-                                                        signature)) {
-          return CheckGenericArgumentsResult::createIsolatedConformanceFailure(
-            req, substReq,
-            TinyPtrVector<ProtocolConformanceRef>(isolatedConformances),
-            *failedProtocol);
+      for (const auto &isolatedConformance : isolatedConformances) {
+        (void)isolatedConformance;
+        if (auto failed =
+                signature->prohibitsIsolatedConformance(req.getFirstType())) {
+            return CheckGenericArgumentsResult::createIsolatedConformanceFailure(
+              req, substReq,
+              TinyPtrVector<ProtocolConformanceRef>(isolatedConformances),
+              failed->second);
+        }
       }
     }
   }
@@ -1181,28 +1183,3 @@ Type StructuralTypeRequest::evaluate(Evaluator &evaluator,
 
   return TypeAliasType::get(typeAlias, parent, genericArgs, result);
 }
-
-std::optional<ProtocolDecl *> swift::typeParameterProhibitsIsolatedConformance(
-    Type type, GenericSignature signature) {
-  if (!type->isTypeParameter())
-    return std::nullopt;
-
-  // An isolated conformance cannot be used in a context where the type
-  // parameter can escape the isolation domain in which the conformance
-  // was formed. To establish this, we look for Sendable or SendableMetatype
-  // requirements on the type parameter itself.
-  ASTContext &ctx = type->getASTContext();
-  auto sendableProto = ctx.getProtocol(KnownProtocolKind::Sendable);
-  auto sendableMetatypeProto =
-      ctx.getProtocol(KnownProtocolKind::SendableMetatype);
-
-  if (sendableProto &&
-      signature->requiresProtocol(type, sendableProto))
-    return sendableProto;
-
-  if (sendableMetatypeProto &&
-          signature->requiresProtocol(type, sendableMetatypeProto))
-    return sendableMetatypeProto;
-
-  return std::nullopt;
-}

lib/Sema/TypeChecker.h

@@ -1535,14 +1535,6 @@ bool maybeDiagnoseMissingImportForMember(const ValueDecl *decl,
 /// source file.
 void diagnoseMissingImports(SourceFile &sf);
 
-/// Determine whether the type parameter has requirements that would prohibit
-/// it from using any isolated conformances.
-///
-/// Returns the protocol to which the type conforms that causes the conflict,
-/// which can be either Sendable or SendableMetatype.
-std::optional<ProtocolDecl *> typeParameterProhibitsIsolatedConformance(
-    Type type, GenericSignature signature);
-
 } // end namespace swift
 
 #endif

lib/Sema/TypeOfReference.cpp

@@ -1230,8 +1230,8 @@ void ConstraintSystem::openGenericRequirement(
 
     // Check whether the given type parameter has requirements that
     // prohibit it from using an isolated conformance.
-    if (typeParameterProhibitsIsolatedConformance(req.getFirstType(),
-                                                  signature))
+    if (signature &&
+        signature->prohibitsIsolatedConformance(req.getFirstType()))
       prohibitIsolatedConformance = true;
 
     openedReq = Requirement(kind, openedFirst, req.getSecondType());

test/Concurrency/isolated_conformance.swift

@@ -153,3 +153,37 @@ func testIsolationConformancesFromOutside(c: C) {
   let _: any P = c // expected-error{{main actor-isolated conformance of 'C' to 'P' cannot be used in nonisolated context}}
   let _ = PWrapper<C>() // expected-error{{main actor-isolated conformance of 'C' to 'P' cannot be used in nonisolated context}}
 }
+
+protocol HasAssociatedType {
+  associatedtype A
+}
+
+func acceptHasAssocWithP<T: HasAssociatedType>(_: T) where T.A: P { }
+
+func acceptSendableHasAssocWithP<T: Sendable & HasAssociatedType>(_: T) where T.A: P { }
+// expected-note@-1{{'acceptSendableHasAssocWithP' declared here}}
+
+
+struct HoldsC: HasAssociatedType {
+  typealias A = C
+}
+
+extension HasAssociatedType {
+  static func acceptAliased<T: P>(_: T.Type) where A == T { }
+}
+
+extension HasAssociatedType where Self: Sendable {
+  static func acceptSendableAliased<T: P>(_: T.Type) where A == T { }
+}
+
+func testIsolatedConformancesOnAssociatedTypes(hc: HoldsC, c: C) {
+  acceptHasAssocWithP(hc)
+  acceptSendableHasAssocWithP(hc) // expected-error{{main actor-isolated conformance of 'C' to 'P' cannot satisfy conformance requirement for a 'Sendable' type parameter }}
+
+  HoldsC.acceptAliased(C.self) // okay
+
+  // FIXME: the following should produce an error, because the isolated
+  // conformance of C: P can cross isolation boundaries via the Sendable Self's
+  // associated type.
+  HoldsC.acceptSendableAliased(C.self)
+}