Merge pull request #84237 from susmonteiro/susmonteiro/cxxrecord-semantics

susmonteiro · web-flow · commit f648dbbbca70 · 2025-09-17T03:05:45.000+01:00
[cxx-interop] Refactor copyability out of CxxRecordSemantics
diff --git a/include/swift/ClangImporter/ClangImporterRequests.h b/include/swift/ClangImporter/ClangImporterRequests.h
@@ -342,15 +342,9 @@ class ObjCInterfaceAndImplementationRequest
 };
 
 enum class CxxRecordSemanticsKind {
-  Trivial,
-  Owned,
-  MoveOnly,
+  Value,
   Reference,
   Iterator,
-  // A record that is either not copyable/movable or not destructible.
-  MissingLifetimeOperation,
-  // A record that has no copy and no move operations
-  UnavailableConstructors,
   // A C++ record that represents a Swift class type exposed to C++ from Swift.
   SwiftClassType
 };
@@ -576,6 +570,59 @@ class ClangTypeEscapability
 void simple_display(llvm::raw_ostream &out, EscapabilityLookupDescriptor desc);
 SourceLoc extractNearestSourceLoc(EscapabilityLookupDescriptor desc);
 
+// Swift value semantics of C++ types
+// These are usually equivalent, with the exception of references.
+// When a reference type is copied, the pointer’s value is copied rather than
+// the object’s storage. This means reference types can be imported as
+// copyable to Swift, even when they are non-copyable in C++.
+enum class CxxValueSemanticsKind {
+  Copyable,
+  MoveOnly,
+  // A record that is either not copyable/movable or not destructible.
+  MissingLifetimeOperation,
+  // A record that has no copy and no move operations
+  UnavailableConstructors,
+};
+
+struct CxxValueSemanticsDescriptor final {
+  const clang::Type *type;
+  ClangImporter::Implementation *importerImpl;
+
+  friend llvm::hash_code hash_value(const CxxValueSemanticsDescriptor &desc) {
+    return llvm::hash_combine(desc.type);
+  }
+
+  friend bool operator==(const CxxValueSemanticsDescriptor &lhs,
+                         const CxxValueSemanticsDescriptor &rhs) {
+    return lhs.type == rhs.type;
+  }
+
+  friend bool operator!=(const CxxValueSemanticsDescriptor &lhs,
+                         const CxxValueSemanticsDescriptor &rhs) {
+    return !(lhs == rhs);
+  }
+};
+
+class CxxValueSemantics
+    : public SimpleRequest<CxxValueSemantics,
+                           CxxValueSemanticsKind(
+                               CxxValueSemanticsDescriptor),
+                           RequestFlags::Cached> {
+public:
+  using SimpleRequest::SimpleRequest;
+
+  bool isCached() const { return true; }
+
+private:
+  friend SimpleRequest;
+
+  CxxValueSemanticsKind evaluate(Evaluator &evaluator,
+                                 CxxValueSemanticsDescriptor desc) const;
+};
+
+void simple_display(llvm::raw_ostream &out, CxxValueSemanticsDescriptor desc);
+SourceLoc extractNearestSourceLoc(CxxValueSemanticsDescriptor desc);
+
 struct CxxDeclExplicitSafetyDescriptor final {
   const clang::Decl *decl;
   bool isClass;
diff --git a/include/swift/ClangImporter/ClangImporterTypeIDZone.def b/include/swift/ClangImporter/ClangImporterTypeIDZone.def
@@ -45,6 +45,9 @@ SWIFT_REQUEST(ClangImporter, CustomRefCountingOperation,
 SWIFT_REQUEST(ClangImporter, ClangTypeEscapability,
               CxxEscapability(EscapabilityLookupDescriptor), Cached,
               NoLocationInfo)
+SWIFT_REQUEST(ClangImporter, CxxValueSemantics,
+              CxxValueSemanticsKind(CxxValueSemanticsDescriptor), Cached,
+              NoLocationInfo)
 SWIFT_REQUEST(ClangImporter, ClangDeclExplicitSafety,
               ExplicitSafety(CxxDeclExplicitSafetyDescriptor), Cached,
               NoLocationInfo)
diff --git a/lib/ClangImporter/ClangImporter.cpp b/lib/ClangImporter/ClangImporter.cpp
@@ -8094,85 +8094,10 @@ bool importer::isViewType(const clang::CXXRecordDecl *decl) {
   return !hasOwnedValueAttr(decl) && hasPointerInSubobjects(decl);
 }
 
-static bool copyConstructorIsDefaulted(const clang::CXXRecordDecl *decl) {
-  auto ctor = llvm::find_if(decl->ctors(), [](clang::CXXConstructorDecl *ctor) {
-    return ctor->isCopyConstructor();
-  });
-
-  assert(ctor != decl->ctor_end());
-  return ctor->isDefaulted();
-}
-
-static bool copyAssignOperatorIsDefaulted(const clang::CXXRecordDecl *decl) {
-  auto copyAssignOp = llvm::find_if(decl->decls(), [](clang::Decl *member) {
-    if (auto method = dyn_cast<clang::CXXMethodDecl>(member))
-      return method->isCopyAssignmentOperator();
-    return false;
-  });
-
-  assert(copyAssignOp != decl->decls_end());
-  return cast<clang::CXXMethodDecl>(*copyAssignOp)->isDefaulted();
-}
-
-/// Recursively checks that there are no user-provided copy constructors or
-/// destructors in any fields or base classes.
-/// Does not check C++ records with specific API annotations.
-static bool isSufficientlyTrivial(const clang::CXXRecordDecl *decl) {
-  // Probably a class template that has not yet been specialized:
-  if (!decl->getDefinition())
-    return true;
-
-  if ((decl->hasUserDeclaredCopyConstructor() &&
-       !copyConstructorIsDefaulted(decl)) ||
-      (decl->hasUserDeclaredCopyAssignment() &&
-       !copyAssignOperatorIsDefaulted(decl)) ||
-      (decl->hasUserDeclaredDestructor() && decl->getDestructor() &&
-       !decl->getDestructor()->isDefaulted()))
-    return false;
-
-  auto checkType = [](clang::QualType t) {
-    if (auto recordType = dyn_cast<clang::RecordType>(t.getCanonicalType())) {
-      if (auto cxxRecord =
-              dyn_cast<clang::CXXRecordDecl>(recordType->getDecl())) {
-        if (hasImportAsRefAttr(cxxRecord) || hasOwnedValueAttr(cxxRecord) ||
-            hasUnsafeAPIAttr(cxxRecord))
-          return true;
-
-        if (!isSufficientlyTrivial(cxxRecord))
-          return false;
-      }
-    }
-
-    return true;
-  };
-
-  for (auto field : decl->fields()) {
-    if (!checkType(field->getType()))
-      return false;
-  }
-
-  for (auto base : decl->bases()) {
-    if (!checkType(base.getType()))
-      return false;
-  }
-
-  return true;
-}
-
-/// Checks if a record provides the required value type lifetime operations
-/// (copy and destroy).
 static bool hasCopyTypeOperations(const clang::CXXRecordDecl *decl) {
-  // Hack for a base type of std::optional from the Microsoft standard library.
-  if (decl->isInStdNamespace() && decl->getIdentifier() &&
-      decl->getName() == "_Optional_construct_base")
-    return true;
-
   if (decl->hasSimpleCopyConstructor())
     return true;
 
-  // If we have no way of copying the type we can't import the class
-  // at all because we cannot express the correct semantics as a swift
-  // struct.
   return llvm::any_of(decl->ctors(), [](clang::CXXConstructorDecl *ctor) {
     return ctor->isCopyConstructor() && !ctor->isDeleted() &&
            !ctor->isIneligibleOrNotSelected() &&
@@ -8183,12 +8108,10 @@ static bool hasCopyTypeOperations(const clang::CXXRecordDecl *decl) {
 }
 
 static bool hasMoveTypeOperations(const clang::CXXRecordDecl *decl) {
-  // If we have no way of copying the type we can't import the class
-  // at all because we cannot express the correct semantics as a swift
-  // struct.
   if (llvm::any_of(decl->ctors(), [](clang::CXXConstructorDecl *ctor) {
         return ctor->isMoveConstructor() &&
-               (ctor->isDeleted() || ctor->getAccess() != clang::AS_public);
+               (ctor->isDeleted() || ctor->isIneligibleOrNotSelected() ||
+                ctor->getAccess() != clang::AS_public);
       }))
     return false;
 
@@ -8201,7 +8124,8 @@ static bool hasMoveTypeOperations(const clang::CXXRecordDecl *decl) {
 
 static bool hasDestroyTypeOperations(const clang::CXXRecordDecl *decl) {
   if (auto dtor = decl->getDestructor()) {
-    if (dtor->isDeleted() || dtor->getAccess() != clang::AS_public) {
+    if (dtor->isDeleted() || dtor->isIneligibleOrNotSelected() ||
+        dtor->getAccess() != clang::AS_public) {
       return false;
     }
     return true;
@@ -8257,49 +8181,17 @@ CxxRecordSemantics::evaluate(Evaluator &evaluator,
 
   auto cxxDecl = dyn_cast<clang::CXXRecordDecl>(decl);
   if (!cxxDecl) {
-    if (hasNonCopyableAttr(decl))
-      return CxxRecordSemanticsKind::MoveOnly;
-
-    return CxxRecordSemanticsKind::Trivial;
+    return CxxRecordSemanticsKind::Value;
   }
 
   if (isSwiftClassType(cxxDecl))
     return CxxRecordSemanticsKind::SwiftClassType;
 
-  if (!hasDestroyTypeOperations(cxxDecl) ||
-      (!hasCopyTypeOperations(cxxDecl) && !hasMoveTypeOperations(cxxDecl))) {
-
-    if (hasConstructorWithUnsupportedDefaultArgs(cxxDecl))
-      return CxxRecordSemanticsKind::UnavailableConstructors;
-
-    return CxxRecordSemanticsKind::MissingLifetimeOperation;
-  }
-
-  if (hasNonCopyableAttr(cxxDecl) && hasMoveTypeOperations(cxxDecl)) {
-    return CxxRecordSemanticsKind::MoveOnly;
-  }
-
-  if (hasOwnedValueAttr(cxxDecl)) {
-    return CxxRecordSemanticsKind::Owned;
-  }
-
   if (hasIteratorAPIAttr(cxxDecl) || isIterator(cxxDecl)) {
     return CxxRecordSemanticsKind::Iterator;
   }
 
-  if (hasCopyTypeOperations(cxxDecl)) {
-    return CxxRecordSemanticsKind::Owned;
-  }
-
-  if (hasMoveTypeOperations(cxxDecl)) {
-    return CxxRecordSemanticsKind::MoveOnly;
-  }
-
-  if (isSufficientlyTrivial(cxxDecl)) {
-    return CxxRecordSemanticsKind::Trivial;
-  }
-
-  llvm_unreachable("Could not classify C++ type.");
+  return CxxRecordSemanticsKind::Value;
 }
 
 ValueDecl *
@@ -8330,6 +8222,74 @@ CxxRecordAsSwiftType::evaluate(Evaluator &evaluator,
   return nullptr;
 }
 
+CxxValueSemanticsKind
+CxxValueSemantics::evaluate(Evaluator &evaluator,
+                            CxxValueSemanticsDescriptor desc) const {
+
+  const auto *type = desc.type;
+
+  auto desugared = type->getUnqualifiedDesugaredType();
+  const auto *recordType = desugared->getAs<clang::RecordType>();
+  if (!recordType)
+    return CxxValueSemanticsKind::Copyable;
+
+  auto recordDecl = recordType->getDecl();
+
+  // When a reference type is copied, the pointer’s value is copied rather than
+  // the object’s storage. This means reference types can be imported as
+  // copyable to Swift, even when they are non-copyable in C++.
+  if (recordHasReferenceSemantics(recordDecl, desc.importerImpl))
+    return CxxValueSemanticsKind::Copyable;
+
+  if (recordDecl->isInStdNamespace()) {
+    // Hack for a base type of std::optional from the Microsoft standard
+    // library.
+    if (recordDecl->getIdentifier() &&
+        recordDecl->getName() == "_Optional_construct_base")
+      return CxxValueSemanticsKind::Copyable;
+  }
+
+  const auto cxxRecordDecl = dyn_cast<clang::CXXRecordDecl>(recordDecl);
+  if (!cxxRecordDecl) {
+    if (hasNonCopyableAttr(recordDecl))
+      return CxxValueSemanticsKind::MoveOnly;
+    return CxxValueSemanticsKind::Copyable;
+  }
+
+  bool isCopyable = hasCopyTypeOperations(cxxRecordDecl);
+  bool isMovable = hasMoveTypeOperations(cxxRecordDecl);
+
+  if (!hasDestroyTypeOperations(cxxRecordDecl) || (!isCopyable && !isMovable)) {
+
+    if (hasConstructorWithUnsupportedDefaultArgs(cxxRecordDecl))
+      return CxxValueSemanticsKind::UnavailableConstructors;
+
+    return CxxValueSemanticsKind::MissingLifetimeOperation;
+  }
+
+  if (hasNonCopyableAttr(cxxRecordDecl) && isMovable)
+    return CxxValueSemanticsKind::MoveOnly;
+
+  if (isCopyable)
+    return CxxValueSemanticsKind::Copyable;
+
+  if (isMovable)
+    return CxxValueSemanticsKind::MoveOnly;
+
+  llvm_unreachable("Could not classify C++ type.");
+}
+
+void swift::simple_display(llvm::raw_ostream &out,
+                           CxxValueSemanticsDescriptor desc) {
+  out << "Checking if '";
+  out << clang::QualType(desc.type, 0).getAsString();
+  out << "' is copyable or movable.";
+}
+
+SourceLoc swift::extractNearestSourceLoc(CxxValueSemanticsDescriptor) {
+  return SourceLoc();
+}
+
 static bool anySubobjectsSelfContained(const clang::CXXRecordDecl *decl) {
   // std::pair and std::tuple might have copy and move constructors, or base
   // classes with copy and move constructors, but they are not self-contained
diff --git a/lib/ClangImporter/ImportDecl.cpp b/lib/ClangImporter/ImportDecl.cpp
@@ -2080,8 +2080,8 @@ namespace {
     bool recordHasMoveOnlySemantics(const clang::RecordDecl *decl) {
       auto semanticsKind = evaluateOrDefault(
           Impl.SwiftContext.evaluator,
-          CxxRecordSemantics({decl, Impl.SwiftContext, &Impl}), {});
-      return semanticsKind == CxxRecordSemanticsKind::MoveOnly;
+          CxxValueSemantics({decl->getTypeForDecl(), &Impl}), {});
+      return semanticsKind == CxxValueSemanticsKind::MoveOnly;
     }
 
     void markReturnsUnsafeNonescapable(AbstractFunctionDecl *fd) {
@@ -3144,11 +3144,11 @@ namespace {
 
       // It is important that we bail on an unimportable record *before* we import
       // any of its members or cache the decl.
-      auto semanticsKind = evaluateOrDefault(
+      auto valueSemanticsKind = evaluateOrDefault(
           Impl.SwiftContext.evaluator,
-          CxxRecordSemantics({decl, Impl.SwiftContext, &Impl}), {});
-      if (semanticsKind == CxxRecordSemanticsKind::MissingLifetimeOperation ||
-          semanticsKind == CxxRecordSemanticsKind::UnavailableConstructors) {
+          CxxValueSemantics({decl->getTypeForDecl(), &Impl}), {});
+      if (valueSemanticsKind == CxxValueSemanticsKind::MissingLifetimeOperation ||
+          valueSemanticsKind == CxxValueSemanticsKind::UnavailableConstructors) {
 
         HeaderLoc loc(decl->getLocation());
         if (hasUnsafeAPIAttr(decl))
@@ -3161,7 +3161,7 @@ namespace {
           Impl.diagnose(loc, diag::api_pattern_attr_ignored, "import_iterator",
                         decl->getNameAsString());
 
-        if (semanticsKind == CxxRecordSemanticsKind::UnavailableConstructors) {
+        if (valueSemanticsKind == CxxValueSemanticsKind::UnavailableConstructors) {
           Impl.addImportDiagnostic(
               decl, Diagnostic(diag::record_unsupported_default_args),
               decl->getLocation());
@@ -3175,7 +3175,12 @@ namespace {
             decl->getLocation());
         return nullptr;
       }
-      if (semanticsKind == CxxRecordSemanticsKind::SwiftClassType) {
+
+      auto cxxRecordsemanticsKind = evaluateOrDefault(
+          Impl.SwiftContext.evaluator,
+          CxxRecordSemantics({decl, Impl.SwiftContext, &Impl}), {});
+
+      if (cxxRecordsemanticsKind == CxxRecordSemanticsKind::SwiftClassType) {
         // FIXME: add a diagnostic here for unsupported imported use of Swift
         // type?
         return nullptr;
@@ -3411,8 +3416,8 @@ namespace {
               decl->getAnonField()->getParent())) {
         auto semanticsKind = evaluateOrDefault(
             Impl.SwiftContext.evaluator,
-            CxxRecordSemantics({parent, Impl.SwiftContext, &Impl}), {});
-        if (semanticsKind == CxxRecordSemanticsKind::MissingLifetimeOperation)
+            CxxValueSemantics({parent->getTypeForDecl(), &Impl}), {});
+        if (semanticsKind == CxxValueSemanticsKind::MissingLifetimeOperation)
           return nullptr;
       }
 
diff --git a/lib/ClangImporter/SwiftDeclSynthesizer.cpp b/lib/ClangImporter/SwiftDeclSynthesizer.cpp
