[APINotes] Add support for SWIFT_RETURED_AS_UNRETAINED_BY_DEFAULT (#138699)

fahadnayyar · web-flow · commit 62a2f0fdc74f · 2025-05-07T13:42:39.000-07:00
This patch adds support in APINotes for annotating C++ user-defined
types with: `swift_attr("returned_as_unretained_by_default")`
This attribute allows to specify a default ownership convention for
return values of `SWIFT_SHARED_REFERENCE` c++ types. Specifically, it
marks all unannotated return values of this type as `unretained` (`+0`)
by default, unless explicitly overridden at the API level using
`swift_attr("returns_retained")` or `swift_attr("returns_unretained")`.

The corresponding Swift compiler support for this annotation enables
developers to suppress warnings about unannotated return ownership in
large codebases while maintaining safe and predictable ownership
semantics. By enabling this in APINotes, library authors can define this
behavior externally without needing to modify C++ source headers
directly.

### Example usage in APINotes:
```
- Name: RefCountedTypeWithDefaultConvention
  SwiftImportAs: reference
  SwiftDefaultOwnership: unretained

```
rdar://150764491
diff --git a/clang/include/clang/APINotes/Types.h b/clang/include/clang/APINotes/Types.h
@@ -737,6 +737,7 @@ class TagInfo : public CommonTypeInfo {
   std::optional<std::string> SwiftImportAs;
   std::optional<std::string> SwiftRetainOp;
   std::optional<std::string> SwiftReleaseOp;
+  std::optional<std::string> SwiftDefaultOwnership;
 
   /// The Swift protocol that this type should be automatically conformed to.
   std::optional<std::string> SwiftConformance;
@@ -786,6 +787,8 @@ class TagInfo : public CommonTypeInfo {
       SwiftRetainOp = RHS.SwiftRetainOp;
     if (!SwiftReleaseOp)
       SwiftReleaseOp = RHS.SwiftReleaseOp;
+    if (!SwiftDefaultOwnership)
+      SwiftDefaultOwnership = RHS.SwiftDefaultOwnership;
 
     if (!SwiftConformance)
       SwiftConformance = RHS.SwiftConformance;
@@ -815,6 +818,7 @@ inline bool operator==(const TagInfo &LHS, const TagInfo &RHS) {
          LHS.SwiftImportAs == RHS.SwiftImportAs &&
          LHS.SwiftRetainOp == RHS.SwiftRetainOp &&
          LHS.SwiftReleaseOp == RHS.SwiftReleaseOp &&
+         LHS.SwiftDefaultOwnership == RHS.SwiftDefaultOwnership &&
          LHS.SwiftConformance == RHS.SwiftConformance &&
          LHS.isFlagEnum() == RHS.isFlagEnum() &&
          LHS.isSwiftCopyable() == RHS.isSwiftCopyable() &&
diff --git a/clang/lib/APINotes/APINotesFormat.h b/clang/lib/APINotes/APINotesFormat.h
@@ -24,7 +24,7 @@ const uint16_t VERSION_MAJOR = 0;
 /// API notes file minor version number.
 ///
 /// When the format changes IN ANY WAY, this number should be incremented.
-const uint16_t VERSION_MINOR = 34; // SwiftReturnOwnership
+const uint16_t VERSION_MINOR = 35; // SwiftDefaultOwnership
 
 const uint8_t kSwiftConforms = 1;
 const uint8_t kSwiftDoesNotConform = 2;
diff --git a/clang/lib/APINotes/APINotesReader.cpp b/clang/lib/APINotes/APINotesReader.cpp
@@ -624,6 +624,13 @@ class TagTableInfo
                                         ReleaseOpLength - 1);
       Data += ReleaseOpLength - 1;
     }
+    unsigned DefaultOwnershipLength =
+        endian::readNext<uint16_t, llvm::endianness::little>(Data);
+    if (DefaultOwnershipLength > 0) {
+      Info.SwiftDefaultOwnership = std::string(
+          reinterpret_cast<const char *>(Data), DefaultOwnershipLength - 1);
+      Data += DefaultOwnershipLength - 1;
+    }
     if (unsigned ConformanceLength =
             endian::readNext<uint16_t, llvm::endianness::little>(Data)) {
       Info.SwiftConformance = std::string(reinterpret_cast<const char *>(Data),
diff --git a/clang/lib/APINotes/APINotesWriter.cpp b/clang/lib/APINotes/APINotesWriter.cpp
@@ -1274,6 +1274,7 @@ class TagTableInfo : public CommonTypeTableInfo<TagTableInfo, TagInfo> {
     return 2 + (TI.SwiftImportAs ? TI.SwiftImportAs->size() : 0) +
            2 + (TI.SwiftRetainOp ? TI.SwiftRetainOp->size() : 0) +
            2 + (TI.SwiftReleaseOp ? TI.SwiftReleaseOp->size() : 0) +
+           2 + (TI.SwiftDefaultOwnership ? TI.SwiftDefaultOwnership->size() : 0) +
            2 + (TI.SwiftConformance ? TI.SwiftConformance->size() : 0) +
            3 + getCommonTypeInfoSize(TI);
     // clang-format on
@@ -1322,6 +1323,12 @@ class TagTableInfo : public CommonTypeTableInfo<TagTableInfo, TagInfo> {
     } else {
       writer.write<uint16_t>(0);
     }
+    if (auto DefaultOwnership = TI.SwiftDefaultOwnership) {
+      writer.write<uint16_t>(DefaultOwnership->size() + 1);
+      OS.write(DefaultOwnership->c_str(), DefaultOwnership->size());
+    } else {
+      writer.write<uint16_t>(0);
+    }
     if (auto Conformance = TI.SwiftConformance) {
       writer.write<uint16_t>(Conformance->size() + 1);
       OS.write(Conformance->c_str(), Conformance->size());
diff --git a/clang/lib/APINotes/APINotesYAMLCompiler.cpp b/clang/lib/APINotes/APINotesYAMLCompiler.cpp
@@ -460,6 +460,7 @@ struct Tag {
   std::optional<std::string> SwiftImportAs;
   std::optional<std::string> SwiftRetainOp;
   std::optional<std::string> SwiftReleaseOp;
+  std::optional<std::string> SwiftDefaultOwnership;
   std::optional<std::string> SwiftConformance;
   std::optional<EnumExtensibilityKind> EnumExtensibility;
   std::optional<bool> FlagEnum;
@@ -500,6 +501,7 @@ template <> struct MappingTraits<Tag> {
     IO.mapOptional("SwiftImportAs", T.SwiftImportAs);
     IO.mapOptional("SwiftReleaseOp", T.SwiftReleaseOp);
     IO.mapOptional("SwiftRetainOp", T.SwiftRetainOp);
+    IO.mapOptional("SwiftDefaultOwnership", T.SwiftDefaultOwnership);
     IO.mapOptional("SwiftConformsTo", T.SwiftConformance);
     IO.mapOptional("EnumExtensibility", T.EnumExtensibility);
     IO.mapOptional("FlagEnum", T.FlagEnum);
@@ -990,6 +992,8 @@ class YAMLConverter {
       TI.SwiftReleaseOp = T.SwiftReleaseOp;
     if (T.SwiftConformance)
       TI.SwiftConformance = T.SwiftConformance;
+    if (T.SwiftDefaultOwnership)
+      TI.SwiftDefaultOwnership = T.SwiftDefaultOwnership;
 
     if (T.SwiftCopyable)
       TI.setSwiftCopyable(T.SwiftCopyable);
diff --git a/clang/lib/Sema/SemaAPINotes.cpp b/clang/lib/Sema/SemaAPINotes.cpp
@@ -643,6 +643,9 @@ static void ProcessAPINotes(Sema &S, TagDecl *D, const api_notes::TagInfo &Info,
   if (auto ReleaseOp = Info.SwiftReleaseOp)
     D->addAttr(
         SwiftAttrAttr::Create(S.Context, "release:" + ReleaseOp.value()));
+  if (auto DefaultOwnership = Info.SwiftDefaultOwnership)
+    D->addAttr(SwiftAttrAttr::Create(
+        S.Context, "returned_as_" + DefaultOwnership.value() + "_by_default"));
 
   if (auto ConformsTo = Info.SwiftConformance)
     D->addAttr(
diff --git a/clang/test/APINotes/Inputs/Headers/SwiftImportAs.apinotes b/clang/test/APINotes/Inputs/Headers/SwiftImportAs.apinotes
@@ -14,6 +14,11 @@ Tags:
   SwiftReleaseOp: RCRelease
   SwiftRetainOp: RCRetain
   SwiftConformsTo: MySwiftModule.MySwiftRefCountedProtocol
+- Name: RefCountedTypeWithDefaultConvention
+  SwiftImportAs: reference
+  SwiftReleaseOp: release
+  SwiftRetainOp: retain
+  SwiftDefaultOwnership: unretained
 - Name: NonCopyableType
   SwiftCopyable: false
   SwiftConformsTo: MySwiftModule.MySwiftNonCopyableProtocol
diff --git a/clang/test/APINotes/Inputs/Headers/SwiftImportAs.h b/clang/test/APINotes/Inputs/Headers/SwiftImportAs.h
@@ -19,3 +19,7 @@ struct CopyableType { int value; };
 
 struct NonEscapableType { int value; };
 struct EscapableType { int value; };
+
+struct RefCountedTypeWithDefaultConvention {};
+inline void retain(RefCountedType *x) {}
+inline void release(RefCountedType *x) {}
diff --git a/clang/test/APINotes/swift-import-as.cpp b/clang/test/APINotes/swift-import-as.cpp
@@ -2,6 +2,7 @@
 // RUN: %clang_cc1 -fmodules -fblocks -fimplicit-module-maps -fmodules-cache-path=%t/ModulesCache -fdisable-module-hash -fapinotes-modules -fsyntax-only -I %S/Inputs/Headers %s -x c++
 // RUN: %clang_cc1 -fmodules -fblocks -fimplicit-module-maps -fmodules-cache-path=%t/ModulesCache -fdisable-module-hash -fapinotes-modules -I %S/Inputs/Headers %s -x c++ -ast-dump -ast-dump-filter ImmortalRefType | FileCheck -check-prefix=CHECK-IMMORTAL %s
 // RUN: %clang_cc1 -fmodules -fblocks -fimplicit-module-maps -fmodules-cache-path=%t/ModulesCache -fdisable-module-hash -fapinotes-modules -I %S/Inputs/Headers %s -x c++ -ast-dump -ast-dump-filter RefCountedType | FileCheck -check-prefix=CHECK-REF-COUNTED %s
+// RUN: %clang_cc1 -fmodules -fblocks -fimplicit-module-maps -fmodules-cache-path=%t/ModulesCache -fdisable-module-hash -fapinotes-modules -I %S/Inputs/Headers %s -x c++ -ast-dump -ast-dump-filter RefCountedTypeWithDefaultConvention | FileCheck -check-prefix=CHECK-REF-COUNTED-DEFAULT %s
 // RUN: %clang_cc1 -fmodules -fblocks -fimplicit-module-maps -fmodules-cache-path=%t/ModulesCache -fdisable-module-hash -fapinotes-modules -I %S/Inputs/Headers %s -x c++ -ast-dump -ast-dump-filter NonCopyableType | FileCheck -check-prefix=CHECK-NON-COPYABLE %s
 // RUN: %clang_cc1 -fmodules -fblocks -fimplicit-module-maps -fmodules-cache-path=%t/ModulesCache -fdisable-module-hash -fapinotes-modules -I %S/Inputs/Headers %s -x c++ -ast-dump -ast-dump-filter CopyableType | FileCheck -check-prefix=CHECK-COPYABLE %s
 // RUN: %clang_cc1 -fmodules -fblocks -fimplicit-module-maps -fmodules-cache-path=%t/ModulesCache -fdisable-module-hash -fapinotes-modules -I %S/Inputs/Headers %s -x c++ -ast-dump -ast-dump-filter NonEscapableType | FileCheck -check-prefix=CHECK-NON-ESCAPABLE %s
@@ -26,6 +27,13 @@
 // CHECK-REF-COUNTED: SwiftAttrAttr {{.+}} <<invalid sloc>> "release:RCRelease"
 // CHECK-REF-COUNTED: SwiftAttrAttr {{.+}} <<invalid sloc>> "conforms_to:MySwiftModule.MySwiftRefCountedProtocol"
 
+// CHECK-REF-COUNTED-DEFAULT: Dumping RefCountedTypeWithDefaultConvention:
+// CHECK-REF-COUNTED-DEFAULT-NEXT: CXXRecordDecl {{.+}} imported in SwiftImportAs {{.+}} struct RefCountedTypeWithDefaultConvention
+// CHECK-REF-COUNTED-DEFAULT: SwiftAttrAttr {{.+}} <<invalid sloc>> "import_reference"
+// CHECK-REF-COUNTED-DEFAULT: SwiftAttrAttr {{.+}} <<invalid sloc>> "retain:retain"
+// CHECK-REF-COUNTED-DEFAULT: SwiftAttrAttr {{.+}} <<invalid sloc>> "release:release"
+// CHECK-REF-COUNTED-DEFAULT: SwiftAttrAttr {{.+}} <<invalid sloc>> "returned_as_unretained_by_default"
+
 // CHECK-NON-COPYABLE: Dumping NonCopyableType:
 // CHECK-NON-COPYABLE-NEXT: CXXRecordDecl {{.+}} imported in SwiftImportAs {{.+}} struct NonCopyableType
 // CHECK-NON-COPYABLE: SwiftAttrAttr {{.+}} <<invalid sloc>> "conforms_to:MySwiftModule.MySwiftNonCopyableProtocol"
